linux-kernel - [PATCH] pcie-xilinx: Support reset GPIO and wait for link-up status

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Message-ID: <20250314145933.27902-1-mike.looijmans@topic.nl>
Date: Fri, 14 Mar 2025 15:59:02 +0100
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: linux-pci@...r.kernel.org
CC: Mike Looijmans <mike.looijmans@...ic.nl>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Michal Simek <michal.simek@....com>,
	Rob Herring <robh@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] pcie-xilinx: Support reset GPIO and wait for link-up status

Support providing the PERST reset signal through a devicetree binding.
Thus the system no longer relies on external components to perform the
bus reset.

When the driver loads, the transceiver may still be in the state of
setting up a link. Wait for that to complete before continuing. This
fixes that the PCIe core does not work when loading the PL bitstream
from userspace. There's only milliseconds between the FPGA boot and the
core initializing in that case, and the link won't be up yet. The design
works when the FPGA was programmed in the bootloader, as that will give
the system hundreds of milliseconds to boot.

As the PCIe spec mentions about 120 ms time to establish a link, we'll
allow up to 200ms before giving up.

Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
---

 drivers/pci/controller/pcie-xilinx.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pcie-xilinx.c b/drivers/pci/controller/pcie-xilinx.c
index 0b534f73a942..cd09deba0ddc 100644
--- a/drivers/pci/controller/pcie-xilinx.c
+++ b/drivers/pci/controller/pcie-xilinx.c
@@ -15,8 +15,10 @@
 #include <linux/irqdomain.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <linux/iopoll.h>
 #include <linux/msi.h>
 #include <linux/of_address.h>
+#include <linux/of_gpio.h>
 #include <linux/of_pci.h>
 #include <linux/of_platform.h>
 #include <linux/of_irq.h>
@@ -126,6 +128,14 @@ static inline bool xilinx_pcie_link_up(struct xilinx_pcie *pcie)
 		XILINX_PCIE_REG_PSCR_LNKUP) ? 1 : 0;
 }
 
+static int xilinx_pci_wait_link_up(struct xilinx_pcie *pcie)
+{
+	u32 val;
+
+	return readl_poll_timeout(pcie->reg_base + XILINX_PCIE_REG_PSCR, val,
+			(val & XILINX_PCIE_REG_PSCR_LNKUP), 2000, 200000);
+}
+
 /**
  * xilinx_pcie_clear_err_interrupts - Clear Error Interrupts
  * @pcie: PCIe port information
@@ -492,8 +502,21 @@ static int xilinx_pcie_init_irq_domain(struct xilinx_pcie *pcie)
 static void xilinx_pcie_init_port(struct xilinx_pcie *pcie)
 {
 	struct device *dev = pcie->dev;
+	struct gpio_desc *perst_gpio;
+
+	perst_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(perst_gpio)) {
+		dev_err(dev, "gpio request failed: %d\n", PTR_ERR(perst_gpio));
+		perst_gpio = NULL;
+	}
+
+	if (perst_gpio) {
+		usleep_range(10, 20); /* Assert the reset for ~10 us */
+		gpiod_set_value_cansleep(perst_gpio, 0);
+		usleep_range(1000, 2000);
+	}
 
-	if (xilinx_pcie_link_up(pcie))
+	if (!xilinx_pci_wait_link_up(pcie))
 		dev_info(dev, "PCIe Link is UP\n");
 	else
 		dev_info(dev, "PCIe Link is DOWN\n");
-- 
2.43.0


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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