[PATCH] PCI: cadence: Set LTSSM Detect Quiet state minimum delay as workaround for training defect.

[Nadeem Athani]

Adding a quirk flag "quirk_detect_quiet_flag" to program the minimum
time that LTSSM waits on entering Detect.Quiet state.
Setting this to 2ms for specific TI j7200 SOC as a workaround to resolve
a link training issue in IP.
In future revisions this setting will not be required.

As per PCIe specification, all Receivers must meet the Z-RX-DC
specification for 2.5 GT/s within 1ms of entering Detect.Quiet LTSSM
substate. The LTSSM must stay in this substate until the ZRXDC
specification for 2.5 GT/s is met.

00 : 0 minimum wait time in Detect.Quiet state.
01 : 100us minimum wait time in Detect.Quiet state.
10 : 1ms minimum wait time in Detect.Quiet state.
11 : 2ms minimum wait time in Detect.Quiet state.

Signed-off-by: Nadeem Athani <nadeem at cadence.com>
---
 drivers/pci/controller/cadence/pcie-cadence-ep.c   | 21 +++++++++++++++++++++
 drivers/pci/controller/cadence/pcie-cadence-host.c | 21 +++++++++++++++++++++
 drivers/pci/controller/cadence/pcie-cadence.h      | 12 ++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/drivers/pci/controller/cadence/pcie-cadence-ep.c b/drivers/pci/controller/cadence/pcie-cadence-ep.c
index 897cdde02bd8..245771f03c21 100644
--- a/drivers/pci/controller/cadence/pcie-cadence-ep.c
+++ b/drivers/pci/controller/cadence/pcie-cadence-ep.c
@@ -552,6 +552,23 @@ static const struct pci_epc_ops cdns_pcie_epc_ops = {
 	.get_features	= cdns_pcie_ep_get_features,
 };
 
+static void cdns_pcie_detect_quiet_min_delay_set(struct cdns_pcie_ep *ep)
+{
+	struct cdns_pcie *pcie = &ep->pcie;
+	u32 delay = 0x3;
+	u32 ltssm_control_cap;
+
+	/*
+	 * Set the LTSSM Detect Quiet state min. delay to 2ms.
+	 */
+
+	ltssm_control_cap = cdns_pcie_readl(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP);
+	ltssm_control_cap = ((ltssm_control_cap &
+			    ~CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK) |
+			    CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay));
+
+	cdns_pcie_writel(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP, ltssm_control_cap);
+}
 
 int cdns_pcie_ep_setup(struct cdns_pcie_ep *ep)
 {
@@ -623,6 +640,10 @@ int cdns_pcie_ep_setup(struct cdns_pcie_ep *ep)
 	ep->irq_pci_addr = CDNS_PCIE_EP_IRQ_PCI_ADDR_NONE;
 	/* Reserve region 0 for IRQs */
 	set_bit(0, &ep->ob_region_map);
+
+	if (ep->quirk_detect_quiet_flag)
+		cdns_pcie_detect_quiet_min_delay_set(ep);
+
 	spin_lock_init(&ep->lock);
 
 	return 0;
diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
index ae1c55503513..ffc2dbeb1240 100644
--- a/drivers/pci/controller/cadence/pcie-cadence-host.c
+++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
@@ -462,6 +462,24 @@ static int cdns_pcie_host_init(struct device *dev,
 	return cdns_pcie_host_init_address_translation(rc);
 }
 
+static void cdns_pcie_detect_quiet_min_delay_set(struct cdns_pcie_rc *rc)
+{
+	struct cdns_pcie *pcie = &rc->pcie;
+	u32 delay = 0x3;
+	u32 ltssm_control_cap;
+
+	/*
+	 * Set the LTSSM Detect Quiet state min. delay to 2ms.
+	 */
+
+	ltssm_control_cap = cdns_pcie_readl(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP);
+	ltssm_control_cap = ((ltssm_control_cap &
+			    ~CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK) |
+			    CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay));
+
+	cdns_pcie_writel(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP, ltssm_control_cap);
+}
+
 int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
 {
 	struct device *dev = rc->pcie.dev;
@@ -498,6 +516,9 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
 		return PTR_ERR(rc->cfg_base);
 	rc->cfg_res = res;
 
+	if (rc->quirk_detect_quiet_flag)
+		cdns_pcie_detect_quiet_min_delay_set(rc);
+
 	ret = cdns_pcie_start_link(pcie);
 	if (ret) {
 		dev_err(dev, "Failed to start link\n");
diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
index 254d2570f8c9..d074475fe887 100644
--- a/drivers/pci/controller/cadence/pcie-cadence.h
+++ b/drivers/pci/controller/cadence/pcie-cadence.h
@@ -189,6 +189,14 @@
 /* AXI link down register */
 #define CDNS_PCIE_AT_LINKDOWN (CDNS_PCIE_AT_BASE + 0x0824)
 
+/* LTSSM Capabilities register */
+#define CDNS_PCIE_LTSSM_CONTROL_CAP             (CDNS_PCIE_LM_BASE + 0x0054)
+#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK  GENMASK(2, 1)
+#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT 1
+#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay) \
+	 (((delay) << CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT) & \
+	 CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK)
+
 enum cdns_pcie_rp_bar {
 	RP_BAR_UNDEFINED = -1,
 	RP_BAR0,
@@ -292,6 +300,7 @@ struct cdns_pcie {
  * @avail_ib_bar: Satus of RP_BAR0, RP_BAR1 and	RP_NO_BAR if it's free or
  *                available
  * @quirk_retrain_flag: Retrain link as quirk for PCIe Gen2
+ * @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
  */
 struct cdns_pcie_rc {
 	struct cdns_pcie	pcie;
@@ -301,6 +310,7 @@ struct cdns_pcie_rc {
 	u32			device_id;
 	bool			avail_ib_bar[CDNS_PCIE_RP_MAX_IB];
 	bool                    quirk_retrain_flag;
+	bool			quirk_detect_quiet_flag;
 };
 
 /**
@@ -331,6 +341,7 @@ struct cdns_pcie_epf {
  *        registers fields (RMW) accessible by both remote RC and EP to
  *        minimize time between read and write
  * @epf: Structure to hold info about endpoint function
+ * @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
  */
 struct cdns_pcie_ep {
 	struct cdns_pcie	pcie;
@@ -345,6 +356,7 @@ struct cdns_pcie_ep {
 	/* protect writing to PCI_STATUS while raising legacy interrupts */
 	spinlock_t		lock;
 	struct cdns_pcie_epf	*epf;
+	bool                    quirk_detect_quiet_flag;
 };
 
 
-- 
2.15.0