linux-kernel - [PATCH 2/2] PCI: cadence: Set LTSSM Detect.Quiet state delay.

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Date:   Tue, 9 Mar 2021 08:31:42 +0100
From:   Nadeem Athani <nadeem@...ence.com>
To:     <tjoseph@...ence.com>, <bhelgaas@...gle.com>, <robh+dt@...nel.org>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lorenzo.pieralisi@....com>,
        <robh@...nel.org>, <kishon@...com>
CC:     <mparab@...ence.com>, <sjakhade@...ence.com>, <nadeem@...ence.com>,
        <pthombar@...ence.com>
Subject: [PATCH 2/2] PCI: cadence: Set LTSSM Detect.Quiet state delay.

The parameter detect_quiet_min_delay can be used to program the minimum
time that LTSSM waits on entering Detect.Quiet state.
00 : 0us minimum wait time in Detect.Quiet state.
01 : 100us minimum wait time in Detect.Quiet state.
10 : 1000us minimum wait time in Detect.Quiet state.
11 : 2000us minimum wait time in Detect.Quiet state.

As per PCIe specification, all Receivers must meet the Z-RX-DC
specification for 2.5 GT/s within 1000us of entering Detect.Quiet LTSSM
substate. The LTSSM must stay in this substate until the ZRXDC
specification for 2.5 GT/s is met.

Signed-off-by: Nadeem Athani <nadeem@...ence.com>
---
 drivers/pci/controller/cadence/pcie-cadence-host.c | 22 ++++++++++++++++++++++
 drivers/pci/controller/cadence/pcie-cadence.h      | 10 ++++++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
index 73dcf8cf98fb..056161b3fe65 100644
--- a/drivers/pci/controller/cadence/pcie-cadence-host.c
+++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
@@ -461,6 +461,20 @@ 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 = rc->detect_quiet_min_delay;
+	u32 ltssm_control_cap;
+
+	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;
@@ -485,6 +499,10 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
 	rc->device_id = 0xffff;
 	of_property_read_u32(np, "device-id", &rc->device_id);
 
+	rc->detect_quiet_min_delay = 0;
+	of_property_read_u32(np, "detect-quiet-min-delay",
+			     &rc->detect_quiet_min_delay);
+
 	pcie->reg_base = devm_platform_ioremap_resource_byname(pdev, "reg");
 	if (IS_ERR(pcie->reg_base)) {
 		dev_err(dev, "missing \"reg\"\n");
@@ -497,6 +515,10 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
 		return PTR_ERR(rc->cfg_base);
 	rc->cfg_res = res;
 
+	/* Default Detect.Quiet state delay is 0 */
+	if (rc->detect_quiet_min_delay)
+		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..f2d3cca2c707 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,
@@ -289,6 +297,7 @@ struct cdns_pcie {
  *            single function at a time
  * @vendor_id: PCI vendor ID
  * @device_id: PCI device ID
+ * @detect_quiet_min_delay: LTSSM Detect Quite state min. delay
  * @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
@@ -299,6 +308,7 @@ struct cdns_pcie_rc {
 	void __iomem		*cfg_base;
 	u32			vendor_id;
 	u32			device_id;
+	u32			detect_quiet_min_delay;
 	bool			avail_ib_bar[CDNS_PCIE_RP_MAX_IB];
 	bool                    quirk_retrain_flag;
 };
-- 
2.15.0