linux-kernel - [PATCH 2/2] PCI: xilinx-cpm: Add support for PCIe RP PERST# signal

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Message-ID: <20250224063046.1438006-3-sai.krishna.musham@amd.com>
Date: Mon, 24 Feb 2025 12:00:46 +0530
From: Sai Krishna Musham <sai.krishna.musham@....com>
To: <bhelgaas@...gle.com>, <lpieralisi@...nel.org>, <kw@...ux.com>,
	<manivannan.sadhasivam@...aro.org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
	<conor+dt@...nel.org>
CC: <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <michal.simek@....com>,
	<bharat.kumar.gogada@....com>, <thippeswamy.havalige@....com>,
	<sai.krishna.musham@....com>
Subject: [PATCH 2/2] PCI: xilinx-cpm: Add support for PCIe RP PERST# signal

Add GPIO-based control for the PCIe Root Port PERST# signal.

According to section 2.2 of the PCIe Electromechanical Specification
(Revision 6.0), PERST# signal has to be deasserted after a delay of
100 ms (TPVPERL) to ensure proper reset sequencing during PCIe
initialization.

Signed-off-by: Sai Krishna Musham <sai.krishna.musham@....com>
---
This patch depends on the following patch series.
https://lore.kernel.org/all/20250217072713.635643-3-thippeswamy.havalige@amd.com/
---
 drivers/pci/controller/pcie-xilinx-cpm.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/pci/controller/pcie-xilinx-cpm.c b/drivers/pci/controller/pcie-xilinx-cpm.c
index 81e8bfae53d0..0e31b85658e6 100644
--- a/drivers/pci/controller/pcie-xilinx-cpm.c
+++ b/drivers/pci/controller/pcie-xilinx-cpm.c
@@ -6,6 +6,8 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
@@ -568,8 +570,29 @@ static int xilinx_cpm_pcie_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct pci_host_bridge *bridge;
 	struct resource_entry *bus;
+	struct gpio_desc *reset_gpio;
 	int err;
 
+	/* Request the GPIO for PCIe reset signal */
+	reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(reset_gpio)) {
+		dev_err(dev, "Failed to request reset GPIO\n");
+		return PTR_ERR(reset_gpio);
+	}
+
+	/* Assert the reset signal */
+	gpiod_set_value(reset_gpio, 0);
+
+	/*
+	 * As per section 2.2 of the PCI Express Card Electromechanical
+	 * Specification (Revision 6.0), the deassertion of the PERST# signal
+	 * should be delayed by 100 ms (TPVPERL).
+	 */
+	msleep(100);
+
+	/* Deassert the reset signal */
+	gpiod_set_value(reset_gpio, 1);
+
 	bridge = devm_pci_alloc_host_bridge(dev, sizeof(*port));
 	if (!bridge)
 		return -ENODEV;
-- 
2.44.1