[PATCH net-next 2/3] Documentation: networking: Convert stmmac documentation to RST format

Jose Abreu Jose.Abreu at synopsys.com
Tue Jan 7 02:37:19 PST 2020


Convert the documentation of the driver to RST format and delete the old
txt and old information that no longer applies.

Also, add some new information.

Signed-off-by: Jose Abreu <Jose.Abreu at synopsys.com>

---
Cc: Giuseppe Cavallaro <peppe.cavallaro at st.com>
Cc: Alexandre Torgue <alexandre.torgue at st.com>
Cc: Jose Abreu <joabreu at synopsys.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Jonathan Corbet <corbet at lwn.net>
Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
Cc: netdev at vger.kernel.org
Cc: linux-doc at vger.kernel.org
Cc: linux-stm32 at st-md-mailman.stormreply.com
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
---
 .../networking/device_drivers/stmicro/stmmac.rst   | 697 +++++++++++++++++++++
 .../networking/device_drivers/stmicro/stmmac.txt   | 401 ------------
 2 files changed, 697 insertions(+), 401 deletions(-)
 create mode 100644 Documentation/networking/device_drivers/stmicro/stmmac.rst
 delete mode 100644 Documentation/networking/device_drivers/stmicro/stmmac.txt

diff --git a/Documentation/networking/device_drivers/stmicro/stmmac.rst b/Documentation/networking/device_drivers/stmicro/stmmac.rst
new file mode 100644
index 000000000000..c34bab3d2df0
--- /dev/null
+++ b/Documentation/networking/device_drivers/stmicro/stmmac.rst
@@ -0,0 +1,697 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+==============================================================
+Linux Driver for the Synopsys(R) Ethernet Controllers "stmmac"
+==============================================================
+
+Authors: Giuseppe Cavallaro <peppe.cavallaro at st.com>,
+Alexandre Torgue <alexandre.torgue at st.com>, Jose Abreu <joabreu at synopsys.com>
+
+Contents
+========
+
+- In This Release
+- Feature List
+- Kernel Configuration
+- Command Line Parameters
+- Driver Information and Notes
+- Debug Information
+- Support
+
+In This Release
+===============
+
+This file describes the stmmac Linux Driver for all the Synopsys(R) Ethernet
+Controllers.
+
+Currently, this network device driver is for all STi embedded MAC/GMAC
+(i.e. 7xxx/5xxx SoCs), SPEAr (arm), Loongson1B (mips) and XILINX XC2V3000
+FF1152AMT0221 D1215994A VIRTEX FPGA board. The Synopsys Ethernet QoS 5.0 IPK
+is also supported.
+
+DesignWare(R) Cores Ethernet MAC 10/100/1000 Universal version 3.70a
+(and older) and DesignWare(R) Cores Ethernet Quality-of-Service version 4.0
+(and upper) have been used for developing this driver as well as
+DesignWare(R) Cores XGMAC - 10G Ethernet MAC.
+
+This driver supports both the platform bus and PCI.
+
+This driver includes support for the following Synopsys(R) DesignWare(R)
+Cores Ethernet Controllers and corresponding minimum and maximum versions:
+
++-------------------------------+--------------+--------------+--------------+
+| Controller Name               | Min. Version | Max. Version | Abbrev. Name |
++===============================+==============+==============+==============+
+| Ethernet MAC Universal        | N/A          | 3.73a        | GMAC         |
++-------------------------------+--------------+--------------+--------------+
+| Ethernet Quality-of-Service   | 4.00a        | N/A          | GMAC4+       |
++-------------------------------+--------------+--------------+--------------+
+| XGMAC - 10G Ethernet MAC      | 2.10a        | N/A          | XGMAC2+      |
++-------------------------------+--------------+--------------+--------------+
+
+For questions related to hardware requirements, refer to the documentation
+supplied with your Ethernet adapter. All hardware requirements listed apply
+to use with Linux.
+
+Feature List
+============
+
+The following features are available in this driver:
+ - GMII/MII/RGMII/SGMII/RMII/XGMII Interface
+ - Half-Duplex / Full-Duplex Operation
+ - Energy Efficient Ethernet (EEE)
+ - IEEE 802.3x PAUSE Packets (Flow Control)
+ - RMON/MIB Counters
+ - IEEE 1588 Timestamping (PTP)
+ - Pulse-Per-Second Output (PPS)
+ - MDIO Clause 22 / Clause 45 Interface
+ - MAC Loopback
+ - ARP Offloading
+ - Automatic CRC / PAD Insertion and Checking
+ - Checksum Offload for Received and Transmitted Packets
+ - Standard or Jumbo Ethernet Packets
+ - Source Address Insertion / Replacement
+ - VLAN TAG Insertion / Replacement / Deletion / Filtering (HASH and PERFECT)
+ - Programmable TX and RX Watchdog and Coalesce Settings
+ - Destination Address Filtering (PERFECT)
+ - HASH Filtering (Multicast)
+ - Layer 3 / Layer 4 Filtering
+ - Remote Wake-Up Detection
+ - Receive Side Scaling (RSS)
+ - Frame Preemption for TX and RX
+ - Programmable Burst Length, Threshold, Queue Size
+ - Multiple Queues (up to 8)
+ - Multiple Scheduling Algorithms (TX: WRR, DWRR, WFQ, SP, CBS, EST, TBS;
+   RX: WRR, SP)
+ - Flexible RX Parser
+ - TCP / UDP Segmentation Offload (TSO, USO)
+ - Split Header (SPH)
+ - Safety Features (ECC Protection, Data Parity Protection)
+ - Selftests using Ethtool
+
+Kernel Configuration
+====================
+
+The kernel configuration option is ``CONFIG_STMMAC_ETH``:
+ - ``CONFIG_STMMAC_PLATFORM``: is to enable the platform driver.
+ - ``CONFIG_STMMAC_PCI``: is to enable the pci driver.
+
+Command Line Parameters
+=======================
+
+If the driver is built as a module the following optional parameters are used
+by entering them on the command line with the modprobe command using this
+syntax (e.g. for PCI module)::
+
+    modprobe stmmac_pci [<option>=<VAL1>,<VAL2>,...]
+
+Driver parameters can be also passed in command line by using::
+
+    stmmaceth=watchdog:100,chain_mode=1
+
+The default value for each parameter is generally the recommended setting,
+unless otherwise noted.
+
+watchdog
+--------
+:Valid Range: 5000-None
+:Default Value: 5000
+
+This parameter overrides the transmit timeout in milliseconds.
+
+debug
+-----
+:Valid Range: 0-16 (0=none,...,16=all)
+:Default Value: 0
+
+This parameter adjusts the level of debug messages displayed in the system
+logs.
+
+phyaddr
+-------
+:Valid Range: 0-31
+:Default Value: -1
+
+This parameter overrides the physical address of the PHY device.
+
+flow_ctrl
+---------
+:Valid Range: 0-3 (0=off,1=rx,2=tx,3=rx/tx)
+:Default Value: 3
+
+This parameter changes the default Flow Control ability.
+
+pause
+-----
+:Valid Range: 0-65535
+:Default Value: 65535
+
+This parameter changes the default Flow Control Pause time.
+
+tc
+--
+:Valid Range: 64-256
+:Default Value: 64
+
+This parameter changes the default HW FIFO Threshold control value.
+
+buf_sz
+------
+:Valid Range: 1536-16384
+:Default Value: 1536
+
+This parameter changes the default RX DMA packet buffer size.
+
+eee_timer
+---------
+:Valid Range: 0-None
+:Default Value: 1000
+
+This parameter changes the default LPI TX Expiration time in milliseconds.
+
+chain_mode
+----------
+:Valid Range: 0-1 (0=off,1=on)
+:Default Value: 0
+
+This parameter changes the default mode of operation from Ring Mode to
+Chain Mode.
+
+Driver Information and Notes
+============================
+
+Transmit Process
+----------------
+
+The xmit method is invoked when the kernel needs to transmit a packet; it sets
+the descriptors in the ring and informs the DMA engine that there is a packet
+ready to be transmitted.
+
+By default, the driver sets the ``NETIF_F_SG`` bit in the features field of
+the ``net_device`` structure, enabling the scatter-gather feature. This is
+true on chips and configurations where the checksum can be done in hardware.
+
+Once the controller has finished transmitting the packet, timer will be
+scheduled to release the transmit resources.
+
+Receive Process
+---------------
+
+When one or more packets are received, an interrupt happens. The interrupts
+are not queued, so the driver has to scan all the descriptors in the ring
+during the receive process.
+
+This is based on NAPI, so the interrupt handler signals only if there is work
+to be done, and it exits. Then the poll method will be scheduled at some
+future point.
+
+The incoming packets are stored, by the DMA, in a list of pre-allocated socket
+buffers in order to avoid the memcpy (zero-copy).
+
+Interrupt Mitigation
+--------------------
+
+The driver is able to mitigate the number of its DMA interrupts using NAPI for
+the reception on chips older than the 3.50. New chips have an HW RX Watchdog
+used for this mitigation.
+
+Mitigation parameters can be tuned by ethtool.
+
+WoL
+---
+
+Wake up on Lan feature through Magic and Unicast frames are supported for the
+GMAC, GMAC4/5 and XGMAC core.
+
+DMA Descriptors
+---------------
+
+Driver handles both normal and alternate descriptors. The latter has been only
+tested on DesignWare(R) Cores Ethernet MAC Universal version 3.41a and later.
+
+stmmac supports DMA descriptor to operate both in dual buffer (RING) and
+linked-list(CHAINED) mode. In RING each descriptor points to two data buffer
+pointers whereas in CHAINED mode they point to only one data buffer pointer.
+RING mode is the default.
+
+In CHAINED mode each descriptor will have pointer to next descriptor in the
+list, hence creating the explicit chaining in the descriptor itself, whereas
+such explicit chaining is not possible in RING mode.
+
+Extended Descriptors
+--------------------
+
+The extended descriptors give us information about the Ethernet payload when
+it is carrying PTP packets or TCP/UDP/ICMP over IP. These are not available on
+GMAC Synopsys(R) chips older than the 3.50. At probe time the driver will
+decide if these can be actually used. This support also is mandatory for PTPv2
+because the extra descriptors are used for saving the hardware timestamps and
+Extended Status.
+
+Ethtool Support
+---------------
+
+Ethtool is supported. For example, driver statistics (including RMON),
+internal errors can be taken using::
+
+    ethtool -S ethX
+
+Ethtool selftests are also supported. This allows to do some early sanity
+checks to the HW using MAC and PHY loopback mechanisms::
+
+    ethtool -t ethX
+
+Jumbo and Segmentation Offloading
+---------------------------------
+
+Jumbo frames are supported and tested for the GMAC. The GSO has been also
+added but it's performed in software. LRO is not supported.
+
+TSO Support
+-----------
+
+TSO (TCP Segmentation Offload) feature is supported by GMAC > 4.x and XGMAC
+chip family. When a packet is sent through TCP protocol, the TCP stack ensures
+that the SKB provided to the low level driver (stmmac in our case) matches
+with the maximum frame len (IP header + TCP header + payload <= 1500 bytes
+(for MTU set to 1500)). It means that if an application using TCP want to send
+a packet which will have a length (after adding headers) > 1514 the packet
+will be split in several TCP packets: The data payload is split and headers
+(TCP/IP ..) are added. It is done by software.
+
+When TSO is enabled, the TCP stack doesn't care about the maximum frame length
+and provide SKB packet to stmmac as it is. The GMAC IP will have to perform
+the segmentation by it self to match with maximum frame length.
+
+This feature can be enabled in device tree through ``snps,tso`` entry.
+
+Energy Efficient Ethernet
+-------------------------
+
+Energy Efficient Ethernet (EEE) enables IEEE 802.3 MAC sublayer along with a
+family of Physical layer to operate in the Low Power Idle (LPI) mode. The EEE
+mode supports the IEEE 802.3 MAC operation at 100Mbps, 1000Mbps and 1Gbps.
+
+The LPI mode allows power saving by switching off parts of the communication
+device functionality when there is no data to be transmitted & received.
+The system on both the side of the link can disable some functionalities and
+save power during the period of low-link utilization. The MAC controls whether
+the system should enter or exit the LPI mode and communicate this to PHY.
+
+As soon as the interface is opened, the driver verifies if the EEE can be
+supported. This is done by looking at both the DMA HW capability register and
+the PHY devices MCD registers.
+
+To enter in TX LPI mode the driver needs to have a software timer that enable
+and disable the LPI mode when there is nothing to be transmitted.
+
+Precision Time Protocol (PTP)
+-----------------------------
+
+The driver supports the IEEE 1588-2002, Precision Time Protocol (PTP), which
+enables precise synchronization of clocks in measurement and control systems
+implemented with technologies such as network communication.
+
+In addition to the basic timestamp features mentioned in IEEE 1588-2002
+Timestamps, new GMAC cores support the advanced timestamp features.
+IEEE 1588-2008 can be enabled when configuring the Kernel.
+
+SGMII/RGMII Support
+-------------------
+
+New GMAC devices provide own way to manage RGMII/SGMII. This information is
+available at run-time by looking at the HW capability register. This means
+that the stmmac can manage auto-negotiation and link status w/o using the
+PHYLIB stuff. In fact, the HW provides a subset of extended registers to
+restart the ANE, verify Full/Half duplex mode and Speed. Thanks to these
+registers, it is possible to look at the Auto-negotiated Link Parter Ability.
+
+Physical
+--------
+
+The driver is compatible with Physical Abstraction Layer to be connected with
+PHY and GPHY devices.
+
+Platform Information
+--------------------
+
+Several information can be passed through the platform and device-tree.
+
+::
+
+    struct plat_stmmacenet_data {
+
+1) Bus identifier::
+
+        int bus_id;
+
+2) PHY Physical Address. If set to -1 the driver will pick the first PHY it
+finds::
+
+        int phy_addr;
+
+3) PHY Device Interface::
+
+        int interface;
+
+4) Specific platform fields for the MDIO bus::
+
+        struct stmmac_mdio_bus_data *mdio_bus_data;
+
+5) Internal DMA parameters::
+
+        struct stmmac_dma_cfg *dma_cfg;
+
+6) Fixed CSR Clock Range selection::
+
+        int clk_csr;
+
+7) HW uses the GMAC core::
+
+        int has_gmac;
+
+8) If set the MAC will use Enhanced Descriptors::
+
+        int enh_desc;
+
+9) Core is able to perform TX Checksum and/or RX Checksum in HW::
+
+        int tx_coe;
+        int rx_coe;
+
+11) Some HWs are not able to perform the csum in HW for over-sized frames due
+to limited buffer sizes. Setting this flag the csum will be done in SW on
+JUMBO frames::
+
+        int bugged_jumbo;
+
+12) Core has the embedded power module::
+
+        int pmt;
+
+13) Force DMA to use the Store and Forward mode or Threshold mode::
+
+        int force_sf_dma_mode;
+        int force_thresh_dma_mode;
+
+15) Force to disable the RX Watchdog feature and switch to NAPI mode::
+
+        int riwt_off;
+
+16) Limit the maximum operating speed and MTU::
+
+        int max_speed;
+        int maxmtu;
+
+18) Number of Multicast/Unicast filters::
+
+        int multicast_filter_bins;
+        int unicast_filter_entries;
+
+20) Limit the maximum TX and RX FIFO size::
+
+        int tx_fifo_size;
+        int rx_fifo_size;
+
+21) Use the specified number of TX and RX Queues::
+
+        u32 rx_queues_to_use;
+        u32 tx_queues_to_use;
+
+22) Use the specified TX and RX scheduling algorithm::
+
+        u8 rx_sched_algorithm;
+        u8 tx_sched_algorithm;
+
+23) Internal TX and RX Queue parameters::
+
+        struct stmmac_rxq_cfg rx_queues_cfg[MTL_MAX_RX_QUEUES];
+        struct stmmac_txq_cfg tx_queues_cfg[MTL_MAX_TX_QUEUES];
+
+24) This callback is used for modifying some syscfg registers (on ST SoCs)
+according to the link speed negotiated by the physical layer::
+
+        void (*fix_mac_speed)(void *priv, unsigned int speed);
+
+25) Callbacks used for calling a custom initialization; This is sometimes
+necessary on some platforms (e.g. ST boxes) where the HW needs to have set
+some PIO lines or system cfg registers. init/exit callbacks should not use
+or modify platform data::
+
+        int (*init)(struct platform_device *pdev, void *priv);
+        void (*exit)(struct platform_device *pdev, void *priv);
+
+26) Perform HW setup of the bus. For example, on some ST platforms this field
+is used to configure the AMBA bridge to generate more efficient STBus traffic::
+
+        struct mac_device_info *(*setup)(void *priv);
+        void *bsp_priv;
+
+27) Internal clocks and rates::
+
+        struct clk *stmmac_clk;
+        struct clk *pclk;
+        struct clk *clk_ptp_ref;
+        unsigned int clk_ptp_rate;
+        unsigned int clk_ref_rate;
+        s32 ptp_max_adj;
+
+28) Main reset::
+
+        struct reset_control *stmmac_rst;
+
+29) AXI Internal Parameters::
+
+        struct stmmac_axi *axi;
+
+30) HW uses GMAC>4 cores::
+
+        int has_gmac4;
+
+31) HW is sun8i based::
+
+        bool has_sun8i;
+
+32) Enables TSO feature::
+
+        bool tso_en;
+
+33) Enables Receive Side Scaling (RSS) feature::
+
+        int rss_en;
+
+34) MAC Port selection::
+
+        int mac_port_sel_speed;
+
+35) Enables TX LPI Clock Gating::
+
+        bool en_tx_lpi_clockgating;
+
+36) HW uses XGMAC>2.10 cores::
+
+        int has_xgmac;
+
+::
+
+    }
+
+For MDIO bus data, we have:
+
+::
+
+    struct stmmac_mdio_bus_data {
+
+1) PHY mask passed when MDIO bus is registered::
+
+        unsigned int phy_mask;
+
+2) List of IRQs, one per PHY::
+
+        int *irqs;
+
+3) If IRQs is NULL, use this for probed PHY::
+
+        int probed_phy_irq;
+
+4) Set to true if PHY needs reset::
+
+        bool needs_reset;
+
+::
+
+    }
+
+For DMA engine configuration, we have:
+
+::
+
+    struct stmmac_dma_cfg {
+
+1) Programmable Burst Length (TX and RX)::
+
+        int pbl;
+
+2) If set, DMA TX / RX will use this value rather than pbl::
+
+        int txpbl;
+        int rxpbl;
+
+3) Enable 8xPBL::
+
+        bool pblx8;
+
+4) Enable Fixed or Mixed burst::
+
+        int fixed_burst;
+        int mixed_burst;
+
+5) Enable Address Aligned Beats::
+
+        bool aal;
+
+6) Enable Enhanced Addressing (> 32 bits)::
+
+        bool eame;
+
+::
+
+    }
+
+For DMA AXI parameters, we have:
+
+::
+
+    struct stmmac_axi {
+
+1) Enable AXI LPI::
+
+        bool axi_lpi_en;
+        bool axi_xit_frm;
+
+2) Set AXI Write / Read maximum outstanding requests::
+
+        u32 axi_wr_osr_lmt;
+        u32 axi_rd_osr_lmt;
+
+3) Set AXI 4KB bursts::
+
+        bool axi_kbbe;
+
+4) Set AXI maximum burst length map::
+
+        u32 axi_blen[AXI_BLEN];
+
+5) Set AXI Fixed burst / mixed burst::
+
+        bool axi_fb;
+        bool axi_mb;
+
+6) Set AXI rebuild incrx mode::
+
+        bool axi_rb;
+
+::
+
+    }
+
+For the RX Queues configuration, we have:
+
+::
+
+    struct stmmac_rxq_cfg {
+
+1) Mode to use (DCB or AVB)::
+
+        u8 mode_to_use;
+
+2) DMA channel to use::
+
+        u32 chan;
+
+3) Packet routing, if applicable::
+
+        u8 pkt_route;
+
+4) Use priority routing, and priority to route::
+
+        bool use_prio;
+        u32 prio;
+
+::
+
+    }
+
+For the TX Queues configuration, we have:
+
+::
+
+    struct stmmac_txq_cfg {
+
+1) Queue weight in scheduler::
+
+        u32 weight;
+
+2) Mode to use (DCB or AVB)::
+
+        u8 mode_to_use;
+
+3) Credit Base Shaper Parameters::
+
+        u32 send_slope;
+        u32 idle_slope;
+        u32 high_credit;
+        u32 low_credit;
+
+4) Use priority scheduling, and priority::
+
+        bool use_prio;
+        u32 prio;
+
+::
+
+    }
+
+Device Tree Information
+-----------------------
+
+Please refer to the following document:
+Documentation/devicetree/bindings/net/snps,dwmac.yaml
+
+HW Capabilities
+---------------
+
+Note that, starting from new chips, where it is available the HW capability
+register, many configurations are discovered at run-time for example to
+understand if EEE, HW csum, PTP, enhanced descriptor etc are actually
+available. As strategy adopted in this driver, the information from the HW
+capability register can replace what has been passed from the platform.
+
+Debug Information
+=================
+
+The driver exports many information i.e. internal statistics, debug
+information, MAC and DMA registers etc.
+
+These can be read in several ways depending on the type of the information
+actually needed.
+
+For example a user can be use the ethtool support to get statistics: e.g.
+using: ``ethtool -S ethX`` (that shows the Management counters (MMC) if
+supported) or sees the MAC/DMA registers: e.g. using: ``ethtool -d ethX``
+
+Compiling the Kernel with ``CONFIG_DEBUG_FS`` the driver will export the
+following debugfs entries:
+
+ - ``descriptors_status``: To show the DMA TX/RX descriptor rings
+ - ``dma_cap``: To show the HW Capabilities
+
+Developer can also use the ``debug`` module parameter to get further debug
+information (please see: NETIF Msg Level).
+
+Support
+=======
+
+If an issue is identified with the released source code on a supported kernel
+with a supported adapter, email the specific information related to the
+issue to netdev at vger.kernel.org
diff --git a/Documentation/networking/device_drivers/stmicro/stmmac.txt b/Documentation/networking/device_drivers/stmicro/stmmac.txt
deleted file mode 100644
index 1ae979fd90d2..000000000000
--- a/Documentation/networking/device_drivers/stmicro/stmmac.txt
+++ /dev/null
@@ -1,401 +0,0 @@
-       STMicroelectronics 10/100/1000 Synopsys Ethernet driver
-
-Copyright (C) 2007-2015  STMicroelectronics Ltd
-Author: Giuseppe Cavallaro <peppe.cavallaro at st.com>
-
-This is the driver for the MAC 10/100/1000 on-chip Ethernet controllers
-(Synopsys IP blocks).
-
-Currently this network device driver is for all STi embedded MAC/GMAC
-(i.e. 7xxx/5xxx SoCs), SPEAr (arm), Loongson1B (mips) and XLINX XC2V3000
-FF1152AMT0221 D1215994A VIRTEX FPGA board.
-
-DWC Ether MAC 10/100/1000 Universal version 3.70a (and older) and DWC Ether
-MAC 10/100 Universal version 4.0 have been used for developing this driver.
-
-This driver supports both the platform bus and PCI.
-
-Please, for more information also visit: www.stlinux.com
-
-1) Kernel Configuration
-The kernel configuration option is STMMAC_ETH:
- Device Drivers ---> Network device support ---> Ethernet (1000 Mbit) --->
- STMicroelectronics 10/100/1000 Ethernet driver (STMMAC_ETH)
-
-CONFIG_STMMAC_PLATFORM: is to enable the platform driver.
-CONFIG_STMMAC_PCI: is to enable the pci driver.
-
-2) Driver parameters list:
-	debug: message level (0: no output, 16: all);
-	phyaddr: to manually provide the physical address to the PHY device;
-	buf_sz: DMA buffer size;
-	tc: control the HW FIFO threshold;
-	watchdog: transmit timeout (in milliseconds);
-	flow_ctrl: Flow control ability [on/off];
-	pause: Flow Control Pause Time;
-	eee_timer: tx EEE timer;
-	chain_mode: select chain mode instead of ring.
-
-3) Command line options
-Driver parameters can be also passed in command line by using:
-	stmmaceth=watchdog:100,chain_mode=1
-
-4) Driver information and notes
-
-4.1) Transmit process
-The xmit method is invoked when the kernel needs to transmit a packet; it sets
-the descriptors in the ring and informs the DMA engine, that there is a packet
-ready to be transmitted.
-By default, the driver sets the NETIF_F_SG bit in the features field of the
-net_device structure, enabling the scatter-gather feature. This is true on
-chips and configurations where the checksum can be done in hardware.
-Once the controller has finished transmitting the packet, timer will be
-scheduled to release the transmit resources.
-
-4.2) Receive process
-When one or more packets are received, an interrupt happens. The interrupts
-are not queued, so the driver has to scan all the descriptors in the ring during
-the receive process.
-This is based on NAPI, so the interrupt handler signals only if there is work
-to be done, and it exits.
-Then the poll method will be scheduled at some future point.
-The incoming packets are stored, by the DMA, in a list of pre-allocated socket
-buffers in order to avoid the memcpy (zero-copy).
-
-4.3) Interrupt mitigation
-The driver is able to mitigate the number of its DMA interrupts
-using NAPI for the reception on chips older than the 3.50.
-New chips have an HW RX-Watchdog used for this mitigation.
-Mitigation parameters can be tuned by ethtool.
-
-4.4) WOL
-Wake up on Lan feature through Magic and Unicast frames are supported for the
-GMAC core.
-
-4.5) DMA descriptors
-Driver handles both normal and alternate descriptors. The latter has been only
-tested on DWC Ether MAC 10/100/1000 Universal version 3.41a and later.
-
-STMMAC supports DMA descriptor to operate both in dual buffer (RING)
-and linked-list(CHAINED) mode. In RING each descriptor points to two
-data buffer pointers whereas in CHAINED mode they point to only one data
-buffer pointer. RING mode is the default.
-
-In CHAINED mode each descriptor will have pointer to next descriptor in
-the list, hence creating the explicit chaining in the descriptor itself,
-whereas such explicit chaining is not possible in RING mode.
-
-4.5.1) Extended descriptors
-The extended descriptors give us information about the Ethernet payload
-when it is carrying PTP packets or TCP/UDP/ICMP over IP.
-These are not available on GMAC Synopsys chips older than the 3.50.
-At probe time the driver will decide if these can be actually used.
-This support also is mandatory for PTPv2 because the extra descriptors
-are used for saving the hardware timestamps and Extended Status.
-
-4.6) Ethtool support
-Ethtool is supported.
-
-For example, driver statistics (including RMON), internal errors can be taken
-using:
-  # ethtool -S ethX
-command
-
-4.7) Jumbo and Segmentation Offloading
-Jumbo frames are supported and tested for the GMAC.
-The GSO has been also added but it's performed in software.
-LRO is not supported.
-
-4.8) Physical
-The driver is compatible with Physical Abstraction Layer to be connected with
-PHY and GPHY devices.
-
-4.9) Platform information
-Several information can be passed through the platform and device-tree.
-
-struct plat_stmmacenet_data {
-	char *phy_bus_name;
-	int bus_id;
-	int phy_addr;
-	int interface;
-	struct stmmac_mdio_bus_data *mdio_bus_data;
-	struct stmmac_dma_cfg *dma_cfg;
-	int clk_csr;
-	int has_gmac;
-	int enh_desc;
-	int tx_coe;
-	int rx_coe;
-	int bugged_jumbo;
-	int pmt;
-	int force_sf_dma_mode;
-	int force_thresh_dma_mode;
-	int riwt_off;
-	int max_speed;
-	int maxmtu;
-	void (*fix_mac_speed)(void *priv, unsigned int speed);
-	void (*bus_setup)(void __iomem *ioaddr);
-	int (*init)(struct platform_device *pdev, void *priv);
-	void (*exit)(struct platform_device *pdev, void *priv);
-	void *bsp_priv;
-	int has_gmac4;
-	bool tso_en;
-};
-
-Where:
- o phy_bus_name: phy bus name to attach to the stmmac.
- o bus_id: bus identifier.
- o phy_addr: the physical address can be passed from the platform.
-	    If it is set to -1 the driver will automatically
-	    detect it at run-time by probing all the 32 addresses.
- o interface: PHY device's interface.
- o mdio_bus_data: specific platform fields for the MDIO bus.
- o dma_cfg: internal DMA parameters
-   o pbl: the Programmable Burst Length is maximum number of beats to
-       be transferred in one DMA transaction.
-       GMAC also enables the 4xPBL by default. (8xPBL for GMAC 3.50 and newer)
-   o txpbl/rxpbl: GMAC and newer supports independent DMA pbl for tx/rx.
-   o pblx8: Enable 8xPBL (4xPBL for core rev < 3.50). Enabled by default.
-   o fixed_burst/mixed_burst/aal
- o clk_csr: fixed CSR Clock range selection.
- o has_gmac: uses the GMAC core.
- o enh_desc: if sets the MAC will use the enhanced descriptor structure.
- o tx_coe: core is able to perform the tx csum in HW.
- o rx_coe: the supports three check sum offloading engine types:
-	   type_1, type_2 (full csum) and no RX coe.
- o bugged_jumbo: some HWs are not able to perform the csum in HW for
-		over-sized frames due to limited buffer sizes.
-		Setting this flag the csum will be done in SW on
-		JUMBO frames.
- o pmt: core has the embedded power module (optional).
- o force_sf_dma_mode: force DMA to use the Store and Forward mode
-		     instead of the Threshold.
- o force_thresh_dma_mode: force DMA to use the Threshold mode other than
-		     the Store and Forward mode.
- o riwt_off: force to disable the RX watchdog feature and switch to NAPI mode.
- o fix_mac_speed: this callback is used for modifying some syscfg registers
-		 (on ST SoCs) according to the link speed negotiated by the
-		 physical layer .
- o bus_setup: perform HW setup of the bus. For example, on some ST platforms
-	     this field is used to configure the AMBA  bridge to generate more
-	     efficient STBus traffic.
- o init/exit: callbacks used for calling a custom initialization;
-	     this is sometime necessary on some platforms (e.g. ST boxes)
-	     where the HW needs to have set some PIO lines or system cfg
-	     registers.  init/exit callbacks should not use or modify
-	     platform data.
- o bsp_priv: another private pointer.
- o has_gmac4: uses GMAC4 core.
- o tso_en: Enables TSO (TCP Segmentation Offload) feature.
-
-For MDIO bus The we have:
-
- struct stmmac_mdio_bus_data {
-	int (*phy_reset)(void *priv);
-	unsigned int phy_mask;
-	int *irqs;
-	int probed_phy_irq;
- };
-
-Where:
- o phy_reset: hook to reset the phy device attached to the bus.
- o phy_mask: phy mask passed when register the MDIO bus within the driver.
- o irqs: list of IRQs, one per PHY.
- o probed_phy_irq: if irqs is NULL, use this for probed PHY.
-
-For DMA engine we have the following internal fields that should be
-tuned according to the HW capabilities.
-
-struct stmmac_dma_cfg {
-	int pbl;
-	int txpbl;
-	int rxpbl;
-	bool pblx8;
-	int fixed_burst;
-	int mixed_burst;
-	bool aal;
-};
-
-Where:
- o pbl: Programmable Burst Length (tx and rx)
- o txpbl: Transmit Programmable Burst Length. Only for GMAC and newer.
-	 If set, DMA tx will use this value rather than pbl.
- o rxpbl: Receive Programmable Burst Length. Only for GMAC and newer.
-	 If set, DMA rx will use this value rather than pbl.
- o pblx8: Enable 8xPBL (4xPBL for core rev < 3.50). Enabled by default.
- o fixed_burst: program the DMA to use the fixed burst mode
- o mixed_burst: program the DMA to use the mixed burst mode
- o aal: Address-Aligned Beats
-
----
-
-Below an example how the structures above are using on ST platforms.
-
- static struct plat_stmmacenet_data stxYYY_ethernet_platform_data = {
-	.has_gmac = 0,
-	.enh_desc = 0,
-	.fix_mac_speed = stxYYY_ethernet_fix_mac_speed,
-				|
-				|-> to write an internal syscfg
-				|   on this platform when the
-				|   link speed changes from 10 to
-				|   100 and viceversa
-	.init = &stmmac_claim_resource,
-				|
-				|-> On ST SoC this calls own "PAD"
-				|   manager framework to claim
-				|   all the resources necessary
-				|   (GPIO ...). The .custom_cfg field
-				|   is used to pass a custom config.
-};
-
-Below the usage of the stmmac_mdio_bus_data: on this SoC, in fact,
-there are two MAC cores: one MAC is for MDIO Bus/PHY emulation
-with fixed_link support.
-
-static struct stmmac_mdio_bus_data stmmac1_mdio_bus = {
-	.phy_reset = phy_reset;
-		|
-		|-> function to provide the phy_reset on this board
-	.phy_mask = 0,
-};
-
-static struct fixed_phy_status stmmac0_fixed_phy_status = {
-	.link = 1,
-	.speed = 100,
-	.duplex = 1,
-};
-
-During the board's device_init we can configure the first
-MAC for fixed_link by calling:
-  fixed_phy_add(PHY_POLL, 1, &stmmac0_fixed_phy_status);
-and the second one, with a real PHY device attached to the bus,
-by using the stmmac_mdio_bus_data structure (to provide the id, the
-reset procedure etc).
-
-Note that, starting from new chips, where it is available the HW capability
-register, many configurations are discovered at run-time for example to
-understand if EEE, HW csum, PTP, enhanced descriptor etc are actually
-available. As strategy adopted in this driver, the information from the HW
-capability register can replace what has been passed from the platform.
-
-4.10) Device-tree support.
-
-Please see the following document:
-	Documentation/devicetree/bindings/net/stmmac.txt
-
-4.11) This is a summary of the content of some relevant files:
- o stmmac_main.c: implements the main network device driver;
- o stmmac_mdio.c: provides MDIO functions;
- o stmmac_pci: this is the PCI driver;
- o stmmac_platform.c: this the platform driver (OF supported);
- o stmmac_ethtool.c: implements the ethtool support;
- o stmmac.h: private driver structure;
- o common.h: common definitions and VFTs;
- o mmc_core.c/mmc.h: Management MAC Counters;
- o stmmac_hwtstamp.c: HW timestamp support for PTP;
- o stmmac_ptp.c: PTP 1588 clock;
- o stmmac_pcs.h: Physical Coding Sublayer common implementation;
- o dwmac-<XXX>.c: these are for the platform glue-logic file; e.g. dwmac-sti.c
-   for STMicroelectronics SoCs.
-
-- GMAC 3.x
- o descs.h: descriptor structure definitions;
- o dwmac1000_core.c: dwmac GiGa core functions;
- o dwmac1000_dma.c: dma functions for the GMAC chip;
- o dwmac1000.h: specific header file for the dwmac GiGa;
- o dwmac100_core: dwmac 100 core code;
- o dwmac100_dma.c: dma functions for the dwmac 100 chip;
- o dwmac1000.h: specific header file for the MAC;
- o dwmac_lib.c: generic DMA functions;
- o enh_desc.c: functions for handling enhanced descriptors;
- o norm_desc.c: functions for handling normal descriptors;
- o chain_mode.c/ring_mode.c:: functions to manage RING/CHAINED modes;
-
-- GMAC4.x generation
- o dwmac4_core.c: dwmac GMAC4.x core functions;
- o dwmac4_desc.c: functions for handling GMAC4.x descriptors;
- o dwmac4_descs.h: descriptor definitions;
- o dwmac4_dma.c: dma functions for the GMAC4.x chip;
- o dwmac4_dma.h: dma definitions for the GMAC4.x chip;
- o dwmac4.h: core definitions for the GMAC4.x chip;
- o dwmac4_lib.c: generic GMAC4.x functions;
-
-4.12) TSO support (GMAC4.x)
-
-TSO (Tcp Segmentation Offload) feature is supported by GMAC 4.x chip family.
-When a packet is sent through TCP protocol, the TCP stack ensures that
-the SKB provided to the low level driver (stmmac in our case) matches with
-the maximum frame len (IP header + TCP header + payload <= 1500 bytes (for
-MTU set to 1500)). It means that if an application using TCP want to send a
-packet which will have a length (after adding headers) > 1514 the packet
-will be split in several TCP packets: The data payload is split and headers
-(TCP/IP ..) are added. It is done by software.
-
-When TSO is enabled, the TCP stack doesn't care about the maximum frame
-length and provide SKB packet to stmmac as it is. The GMAC IP will have to
-perform the segmentation by it self to match with maximum frame length.
-
-This feature can be enabled in device tree through "snps,tso" entry.
-
-5) Debug Information
-
-The driver exports many information i.e. internal statistics,
-debug information, MAC and DMA registers etc.
-
-These can be read in several ways depending on the
-type of the information actually needed.
-
-For example a user can be use the ethtool support
-to get statistics: e.g. using: ethtool -S ethX
-(that shows the Management counters (MMC) if supported)
-or sees the MAC/DMA registers: e.g. using: ethtool -d ethX
-
-Compiling the Kernel with CONFIG_DEBUG_FS the driver will export the following
-debugfs entries:
-
-/sys/kernel/debug/stmmaceth/descriptors_status
-  To show the DMA TX/RX descriptor rings
-
-Developer can also use the "debug" module parameter to get further debug
-information (please see: NETIF Msg Level).
-
-6) Energy Efficient Ethernet
-
-Energy Efficient Ethernet(EEE) enables IEEE 802.3 MAC sublayer along
-with a family of Physical layer to operate in the Low power Idle(LPI)
-mode. The EEE mode supports the IEEE 802.3 MAC operation at 100Mbps,
-1000Mbps & 10Gbps.
-
-The LPI mode allows power saving by switching off parts of the
-communication device functionality when there is no data to be
-transmitted & received. The system on both the side of the link can
-disable some functionalities & save power during the period of low-link
-utilization. The MAC controls whether the system should enter or exit
-the LPI mode & communicate this to PHY.
-
-As soon as the interface is opened, the driver verifies if the EEE can
-be supported. This is done by looking at both the DMA HW capability
-register and the PHY devices MCD registers.
-To enter in Tx LPI mode the driver needs to have a software timer
-that enable and disable the LPI mode when there is nothing to be
-transmitted.
-
-7) Precision Time Protocol (PTP)
-The driver supports the IEEE 1588-2002, Precision Time Protocol (PTP),
-which enables precise synchronization of clocks in measurement and
-control systems implemented with technologies such as network
-communication.
-
-In addition to the basic timestamp features mentioned in IEEE 1588-2002
-Timestamps, new GMAC cores support the advanced timestamp features.
-IEEE 1588-2008 that can be enabled when configure the Kernel.
-
-8) SGMII/RGMII support
-New GMAC devices provide own way to manage RGMII/SGMII.
-This information is available at run-time by looking at the
-HW capability register. This means that the stmmac can manage
-auto-negotiation and link status w/o using the PHYLIB stuff.
-In fact, the HW provides a subset of extended registers to
-restart the ANE, verify Full/Half duplex mode and Speed.
-Thanks to these registers, it is possible to look at the
-Auto-negotiated Link Parter Ability.
-- 
2.7.4




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