linux-kernel - [PATCH v5] PCI: j721e: Delay T_PVPERL+TPERST

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Message-ID: <20230817093619.1079267-1-a-verma1@ti.com>
Date:   Thu, 17 Aug 2023 15:06:19 +0530
From:   Achal Verma <a-verma1@...com>
To:     Vignesh Raghavendra <vigneshr@...com>,
        Tom Joseph <tjoseph@...ence.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczy_ski <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     <linux-omap@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Achal Verma <a-verma1@...com>
Subject: [PATCH v5] PCI: j721e: Delay T_PVPERL+TPERST_CLK before PERST# inactive

As per the PCIe Card Electromechanical specification REV. 5.0, PERST#
signal should be de-asserted after minimum 100ms from the time power-rails
achieve specified operating limits and 100us after reference clock gets
stable.

>From PCIe Card Electromechanical specification REV. 5.0 section 2.9.2:
TPVPERL: Power stable to PERST# inactive - 100ms
TPERST_CLK: REFCLK stable before PERST# inactive - 100us

Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver")
Signed-off-by: Achal Verma <a-verma1@...com>
---
 drivers/pci/controller/cadence/pci-j721e.c | 30 +++++++++++-----------
 drivers/pci/pci.h                          |  3 +++
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
index e70213c9060a..b09924b010ab 100644
--- a/drivers/pci/controller/cadence/pci-j721e.c
+++ b/drivers/pci/controller/cadence/pci-j721e.c
@@ -34,6 +34,8 @@
 #define J721E_PCIE_USER_LINKSTATUS	0x14
 #define LINK_STATUS			GENMASK(1, 0)
 
+#define PERST_INACTIVE_US (PCIE_TPVPERL_MS*USEC_PER_MSEC + PCIE_TPERST_CLK_US)
+
 enum link_status {
 	NO_RECEIVERS_DETECTED,
 	LINK_TRAINING_IN_PROGRESS,
@@ -359,7 +361,7 @@ static int j721e_pcie_probe(struct platform_device *pdev)
 	struct j721e_pcie *pcie;
 	struct cdns_pcie_rc *rc = NULL;
 	struct cdns_pcie_ep *ep = NULL;
-	struct gpio_desc *gpiod;
+	struct gpio_desc *perst_gpiod;
 	void __iomem *base;
 	struct clk *clk;
 	u32 num_lanes;
@@ -468,11 +470,10 @@ static int j721e_pcie_probe(struct platform_device *pdev)
 
 	switch (mode) {
 	case PCI_MODE_RC:
-		gpiod = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
-		if (IS_ERR(gpiod)) {
-			ret = PTR_ERR(gpiod);
-			if (ret != -EPROBE_DEFER)
-				dev_err(dev, "Failed to get reset GPIO\n");
+		perst_gpiod = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
+		if (IS_ERR(perst_gpiod)) {
+			ret = PTR_ERR(perst_gpiod);
+			dev_err(dev, "Failed to get reset GPIO\n");
 			goto err_get_sync;
 		}
 
@@ -498,16 +499,15 @@ static int j721e_pcie_probe(struct platform_device *pdev)
 
 		/*
 		 * "Power Sequencing and Reset Signal Timings" table in
-		 * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 3.0
-		 * indicates PERST# should be deasserted after minimum of 100us
-		 * once REFCLK is stable. The REFCLK to the connector in RC
-		 * mode is selected while enabling the PHY. So deassert PERST#
-		 * after 100 us.
+		 * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 5.0
+		 * indicates PERST# should be deasserted after minimum of 100ms
+		 * after power rails achieve specified operating limits and
+		 * 100us after reference clock gets stable.
+		 * PERST_INACTIVE_US accounts for both delays.
 		 */
-		if (gpiod) {
-			usleep_range(100, 200);
-			gpiod_set_value_cansleep(gpiod, 1);
-		}
+
+		fsleep(PERST_INACTIVE_US);
+		gpiod_set_value_cansleep(perst_gpiod, 1);
 
 		ret = cdns_pcie_host_setup(rc);
 		if (ret < 0) {
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index a4c397434057..80d520be34e6 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -13,6 +13,9 @@
 
 #define PCIE_LINK_RETRAIN_TIMEOUT_MS	1000
 
+#define PCIE_TPVPERL_MS		100	/* see PCIe CEM r5.0, sec 2.9.2 */
+#define PCIE_TPERST_CLK_US	100
+
 extern const unsigned char pcie_link_speed[];
 extern bool pci_early_dump;
 
-- 
2.25.1