linux-kernel - [PATCH v2] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL

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Message-ID: <20241104074420.1862932-1-s-vadapalli@ti.com>
Date: Mon, 4 Nov 2024 13:14:20 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: <bhelgaas@...gle.com>, <lpieralisi@...nel.org>, <kw@...ux.com>,
        <robh@...nel.org>, <vigneshr@...com>,
        <manivannan.sadhasivam@...aro.org>, <kishon@...nel.org>,
        <thomas.richard@...tlin.com>
CC: <linux-omap@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>, <s-vadapalli@...com>
Subject: [PATCH v2] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL_MS ms

According to Section 2.2 of the PCI Express Card Electromechanical
Specification (Revision 5.1), in order to ensure that the power and the
reference clock are stable, PERST# has to be deasserted after a delay of
100 milliseconds (TPVPERL). Currently, it is being assumed that the power
is already stable, which is not necessarily true. Hence, change the delay
to PCIE_T_PVPERL_MS to guarantee that power and reference clock are stable.

Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver")
Fixes: f96b69713733 ("PCI: j721e: Use T_PERST_CLK_US macro")
Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
---

Hello,

This patch is based on commit
59b723cd2adb Linux 6.12-rc6
of Mainline Linux.

v1:
https://lore.kernel.org/r/20241022083147.2773123-1-s-vadapalli@ti.com/
Changes since v1:
- Rebased patch on Linux 6.12-rc6
- Based on Krzysztof's feedback at:
  https://lore.kernel.org/r/20241102141914.GA3440781@rocinante/
  PCIE_T_PERST_CLK_US has been replaced with PCIE_T_PVPERL_MS in
  j721e_pcie_probe() as well.
- Added Fixes tag corresponding to the above change in the commit
  message.

Regards,
Siddharth.

 drivers/pci/controller/cadence/pci-j721e.c | 26 ++++++++++------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
index 284f2e0e4d26..e091c3e55b5c 100644
--- a/drivers/pci/controller/cadence/pci-j721e.c
+++ b/drivers/pci/controller/cadence/pci-j721e.c
@@ -572,15 +572,14 @@ static int j721e_pcie_probe(struct platform_device *pdev)
 		pcie->refclk = clk;
 
 		/*
-		 * The "Power Sequencing and Reset Signal Timings" table of the
-		 * PCI Express Card Electromechanical Specification, Revision
-		 * 5.1, Section 2.9.2, Symbol "T_PERST-CLK", 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.
+		 * Section 2.2 of the PCI Express Card Electromechanical
+		 * Specification (Revision 5.1) mandates that the deassertion
+		 * of the PERST# signal should be delayed by 100 ms (TPVPERL).
+		 * This shall ensure that the power and the reference clock
+		 * are stable.
 		 */
 		if (gpiod) {
-			fsleep(PCIE_T_PERST_CLK_US);
+			msleep(PCIE_T_PVPERL_MS);
 			gpiod_set_value_cansleep(gpiod, 1);
 		}
 
@@ -671,15 +670,14 @@ static int j721e_pcie_resume_noirq(struct device *dev)
 			return ret;
 
 		/*
-		 * The "Power Sequencing and Reset Signal Timings" table of the
-		 * PCI Express Card Electromechanical Specification, Revision
-		 * 5.1, Section 2.9.2, Symbol "T_PERST-CLK", 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.
+		 * Section 2.2 of the PCI Express Card Electromechanical
+		 * Specification (Revision 5.1) mandates that the deassertion
+		 * of the PERST# signal should be delayed by 100 ms (TPVPERL).
+		 * This shall ensure that the power and the reference clock
+		 * are stable.
 		 */
 		if (pcie->reset_gpio) {
-			fsleep(PCIE_T_PERST_CLK_US);
+			msleep(PCIE_T_PVPERL_MS);
 			gpiod_set_value_cansleep(pcie->reset_gpio, 1);
 		}
 
-- 
2.40.1