linux-kernel - [PATCH v2] PCI: j721e: Delay 100ms T_PVPERL from power stable to PERST# inactive

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Date:   Thu, 6 Jul 2023 10:04:38 +0530
From:   Achal Verma <a-verma1@...com>
To:     Vignesh Raghavendra <vigneshr@...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 v2] PCI: j721e: Delay 100ms T_PVPERL from power stable to 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
become stable.
So, to ensure 100ms delay to give sufficient time for power-rails and
refclk to become stable, change delay from 100us to 100ms.

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

Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver")
Signed-off-by: Achal Verma <a-verma1@...com>
---
 drivers/pci/controller/cadence/pci-j721e.c | 11 +++++------
 drivers/pci/pci.h                          |  2 ++
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
index e70213c9060a..a3c8273b7320 100644
--- a/drivers/pci/controller/cadence/pci-j721e.c
+++ b/drivers/pci/controller/cadence/pci-j721e.c
@@ -498,14 +498,13 @@ 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
+		 * within this period reference clock should also become stable.
 		 */
 		if (gpiod) {
-			usleep_range(100, 200);
+			msleep(PCI_TPVPERL_DELAY);
 			gpiod_set_value_cansleep(gpiod, 1);
 		}
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index a4c397434057..7482cff16fef 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -13,6 +13,8 @@
 
 #define PCIE_LINK_RETRAIN_TIMEOUT_MS	1000
 
+#define PCI_TPVPERL_DELAY	100	/* msec; see PCIe r5.0, sec 2.9.2 */
+
 extern const unsigned char pcie_link_speed[];
 extern bool pci_early_dump;
 
-- 
2.25.1