[PATCH 1/2] serial/imx: add DMA support
Huang Shijie
b32955 at freescale.com
Fri Apr 27 05:46:22 EDT 2012
于 2012年04月27日 16:22, Russell King - ARM Linux 写道:
> On Fri, Apr 27, 2012 at 03:00:39PM +0800, Huang Shijie wrote:
>> 于 2012年04月26日 19:11, Russell King - ARM Linux 写道:
>>> On Thu, Apr 26, 2012 at 06:37:11PM +0800, Huang Shijie wrote:
>>>> Add the DMA support for uart RX and TX.
>>>>
>>>> Signed-off-by: Huang Shijie<b32955 at freescale.com>
>>>> ---
>>> Apart from the comments below,
>>>
>>> 1. How do you deal with transmitting the high-priority XON/XOFF
>>> characters (port->x_char) which occur with s/w flow control and
>>> the tty buffers fill up?
>>> 2. How do you deal with flow control in general? IOW, what happens
>>> when the remote end deasserts your CTS with h/w flow control enabled.
If the remote end deasserts my CTS, it means the remote will not send
any data.
My DMA for RX will expire in the following steps:
[1] the UART only waits for 32 bytes time long
[2] the UART triggers an IDLE Condition Detect DMA.
[3] the dma_rx_callback() will release the DMA for Rx.
>>> How does your end deal with sending RTS according to flow control
>>> conditions?
>>>
If a CTS is received after we sent out a RTS, it will follow the steps:
imx_int() --> imx_rtsint() --> uart_handle_cts_change() -->start_tx()
The start_tx() will create an TX DMA operation, and send out the data.
>>> i
>> The UART uses the DMA for RX/TX with the hardware flow control (RTS/CTS)
>> enabled all the time.
> Your answer is too vague. Please try again.
>
>> If we use the software flow control(XON/XOFF), we should not enable the DMA.
>> I think i should add more comments about this issue.
>>
>> For example:
>> The MX6Q arm2 has two uarts, one with the DMA disabled is used for debug,
>> the other one with the DMA/RTS.CTS enabled can be used for the Bluetooth.
>>>> .../bindings/tty/serial/fsl-imx-uart.txt | 7 +
>>>> drivers/tty/serial/imx.c | 386 +++++++++++++++++++-
>>>> 2 files changed, 389 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt b/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
>>>> index a9c0406..f27489d 100644
>>>> --- a/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
>>>> +++ b/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
>>>> @@ -8,6 +8,10 @@ Required properties:
>>>> Optional properties:
>>>> - fsl,uart-has-rtscts : Indicate the uart has rts and cts
>>>> - fsl,irda-mode : Indicate the uart supports irda mode
>>>> +- fsl,enable-dma : Indicate the uart supports DMA
>>>> +- fsl,uart-dma-events : contains the DMA events for RX and TX,
>>>> + The first is the RX event, while the other is TX.
>>>> +- fsl,enable-dte: Indicate the uart works in DTE mode
>>>>
>>>> Example:
>>>>
>>>> @@ -16,4 +20,7 @@ uart at 73fbc000 {
>>>> reg =<0x73fbc000 0x4000>;
>>>> interrupts =<31>;
>>>> fsl,uart-has-rtscts;
>>>> + fsl,enable-dma;
>>>> + fsl,uart-dma-events =<xx xx>;
>>>> + fsl,enable-dte;
>>>> };
>>>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>>>> index e7fecee..65ba24d 100644
>>>> --- a/drivers/tty/serial/imx.c
>>>> +++ b/drivers/tty/serial/imx.c
>>>> @@ -47,9 +47,11 @@
>>>> #include<linux/slab.h>
>>>> #include<linux/of.h>
>>>> #include<linux/of_device.h>
>>>> +#include<linux/dma-mapping.h>
>>>>
>>>> #include<asm/io.h>
>>>> #include<asm/irq.h>
>>>> +#include<mach/dma.h>
>>>> #include<mach/imx-uart.h>
>>>>
>>>> /* Register definitions */
>>>> @@ -82,6 +84,7 @@
>>>> #define UCR1_ADBR (1<<14) /* Auto detect baud rate */
>>>> #define UCR1_TRDYEN (1<<13) /* Transmitter ready interrupt enable */
>>>> #define UCR1_IDEN (1<<12) /* Idle condition interrupt */
>>>> +#define UCR1_ICD_REG(x) (((x)& 3)<< 10) /* idle condition detect */
>>>> #define UCR1_RRDYEN (1<<9) /* Recv ready interrupt enable */
>>>> #define UCR1_RDMAEN (1<<8) /* Recv ready DMA enable */
>>>> #define UCR1_IREN (1<<7) /* Infrared interface enable */
>>>> @@ -125,6 +128,7 @@
>>>> #define UCR4_ENIRI (1<<8) /* Serial infrared interrupt enable */
>>>> #define UCR4_WKEN (1<<7) /* Wake interrupt enable */
>>>> #define UCR4_REF16 (1<<6) /* Ref freq 16 MHz */
>>>> +#define UCR4_IDDMAEN (1<<6) /* DMA IDLE Condition Detected */
>>>> #define UCR4_IRSC (1<<5) /* IR special case */
>>>> #define UCR4_TCEN (1<<3) /* Transmit complete interrupt enable */
>>>> #define UCR4_BKEN (1<<2) /* Break condition interrupt enable */
>>>> @@ -134,6 +138,7 @@
>>>> #define UFCR_RFDIV (7<<7) /* Reference freq divider mask */
>>>> #define UFCR_RFDIV_REG(x) (((x)< 7 ? 6 - (x) : 6)<< 7)
>>>> #define UFCR_TXTL_SHF 10 /* Transmitter trigger level shift */
>>>> +#define UFCR_DCEDTE (1<<6)
>>>> #define USR1_PARITYERR (1<<15) /* Parity error interrupt flag */
>>>> #define USR1_RTSS (1<<14) /* RTS pin status */
>>>> #define USR1_TRDY (1<<13) /* Transmitter ready interrupt/dma flag */
>>>> @@ -200,12 +205,27 @@ struct imx_port {
>>>> unsigned int old_status;
>>>> int txirq,rxirq,rtsirq;
>>>> unsigned int have_rtscts:1;
>>>> + unsigned int enable_dte:1;
>>>> + unsigned int enable_dma:1;
>>>> unsigned int use_irda:1;
>>>> unsigned int irda_inv_rx:1;
>>>> unsigned int irda_inv_tx:1;
>>>> unsigned short trcv_delay; /* transceiver delay */
>>>> struct clk *clk;
>>>> struct imx_uart_data *devdata;
>>>> +
>>>> + /* DMA fields */
>>>> + unsigned int dma_req_rx;
>>>> + unsigned int dma_req_tx;
>>>> + struct imx_dma_data dma_data;
>>>> + struct dma_chan *dma_chan_rx, *dma_chan_tx;
>>>> + struct scatterlist rx_sgl, tx_sgl[2];
>>>> + void *rx_buf;
>>>> + unsigned int rx_bytes, tx_bytes;
>>>> + struct work_struct tsk_dma_rx, tsk_dma_tx;
>>> Why do you need a work struct to deal with DMA?
>>>
>> The uart uses the SDMA (drivers/dma/imx-sdma.c). And the SDMA may
>> schedule out in :
>> sdma_prep_slave_sg() --> sdma_load_contex() -->sdma_run_channel() .
> It should not. prep_slave_sg() must be callable from atomic contexts.
>
the Documentation/dmaengine.txt does not explicitly force all the dma
engine driver
to do so.
Add more comments for it in Documentation/dmaengine.txt?
>> This callback is called from IRQ context, with all the IRQ disabled. see:
>> sdma_int_handler() -->mxc_sdma_handle_channel() -->
>> mxc_sdma_handle_channel_normal()
>> --> .callback().
> That's a bug in your dmaengine driver.
>
OK, it's really a bug in the sdma driver.
thanks.
Best Regards
Huang Shijie
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