PCI: rockchip-ep: Handle PERST# signal in EP mode

Currently, the Rockchip PCIe endpoint controller driver does not handle
the PERST# signal, which prevents detecting when link training should
actually be started or if the host resets the device. This however can
be supported using the controller reset_gpios property set as an input
GPIO for endpoint mode.

Modify the Rockchip PCI endpoint controller driver to get the reset_gpio
and its associated interrupt which is serviced using a threaded IRQ with
the function rockchip_pcie_ep_perst_irq_thread() as handler.

This handler function notifies a link down event corresponding to the RC
side asserting the PERST# signal using pci_epc_linkdown() when the gpio
is high. Once the gpio value goes down, corresponding to the RC
de-asserting the PERST# signal, link training is started. The polarity
of the gpio interrupt trigger is changed from high to low after the RC
asserted PERST#, and conversely changed from low to high after the RC
de-asserts PERST#.

Also, given that the host mode controller and the endpoint mode
controller use two different property names for the same PERST# signal
(ep_gpios property and reset_gpios property respectively), for clarity,
rename the ep_gpio field of struct rockchip_pcie to perst_gpio.

Link: https://lore.kernel.org/r/20241017015849.190271-14-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
[kwilczynski: make log messages consistent, add missing include]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: damien-lemoal

drivers/pci/controller/pcie-rockchip-ep.c

@@ -10,8 +10,10 @@
 
 #include <linux/configfs.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/iopoll.h>
 #include <linux/kernel.h>
+#include <linux/irq.h>
 #include <linux/of.h>
 #include <linux/pci-epc.h>
 #include <linux/platform_device.h>
@@ -50,6 +52,9 @@ struct rockchip_pcie_ep {
 	u64			irq_pci_addr;
 	u8			irq_pci_fn;
 	u8			irq_pending;
+	int			perst_irq;
+	bool			perst_asserted;
+	bool			link_up;
 	struct delayed_work	link_training;
 };
 
@@ -470,13 +475,17 @@ static int rockchip_pcie_ep_start(struct pci_epc *epc)
 
 	rockchip_pcie_write(rockchip, cfg, PCIE_CORE_PHY_FUNC_CFG);
 
+	if (rockchip->perst_gpio)
+		enable_irq(ep->perst_irq);
+
 	/* Enable configuration and start link training */
 	rockchip_pcie_write(rockchip,
 			    PCIE_CLIENT_LINK_TRAIN_ENABLE |
 			    PCIE_CLIENT_CONF_ENABLE,
 			    PCIE_CLIENT_CONFIG);
 
-	schedule_delayed_work(&ep->link_training, 0);
+	if (!rockchip->perst_gpio)
+		schedule_delayed_work(&ep->link_training, 0);
 
 	return 0;
 }
@@ -486,6 +495,11 @@ static void rockchip_pcie_ep_stop(struct pci_epc *epc)
 	struct rockchip_pcie_ep *ep = epc_get_drvdata(epc);
 	struct rockchip_pcie *rockchip = &ep->rockchip;
 
+	if (rockchip->perst_gpio) {
+		ep->perst_asserted = true;
+		disable_irq(ep->perst_irq);
+	}
+
 	cancel_delayed_work_sync(&ep->link_training);
 
 	/* Stop link training and disable configuration */
@@ -551,6 +565,13 @@ static void rockchip_pcie_ep_link_training(struct work_struct *work)
 	if (!rockchip_pcie_ep_link_up(rockchip))
 		goto again;
 
+	/*
+	 * If PERST# was asserted while polling the link, do not notify
+	 * the function.
+	 */
+	if (ep->perst_asserted)
+		return;
+
 	val = rockchip_pcie_read(rockchip, PCIE_CLIENT_BASIC_STATUS0);
 	dev_info(dev,
 		 "link up (negotiated speed: %sGT/s, width: x%lu)\n",
@@ -560,13 +581,111 @@ static void rockchip_pcie_ep_link_training(struct work_struct *work)
 
 	/* Notify the function */
 	pci_epc_linkup(ep->epc);
+	ep->link_up = true;
 
 	return;
 
 again:
 	schedule_delayed_work(&ep->link_training, msecs_to_jiffies(5));
 }
 
+static void rockchip_pcie_ep_perst_assert(struct rockchip_pcie_ep *ep)
+{
+	struct rockchip_pcie *rockchip = &ep->rockchip;
+
+	dev_dbg(rockchip->dev, "PERST# asserted, link down\n");
+
+	if (ep->perst_asserted)
+		return;
+
+	ep->perst_asserted = true;
+
+	cancel_delayed_work_sync(&ep->link_training);
+
+	if (ep->link_up) {
+		pci_epc_linkdown(ep->epc);
+		ep->link_up = false;
+	}
+}
+
+static void rockchip_pcie_ep_perst_deassert(struct rockchip_pcie_ep *ep)
+{
+	struct rockchip_pcie *rockchip = &ep->rockchip;
+
+	dev_dbg(rockchip->dev, "PERST# de-asserted, starting link training\n");
+
+	if (!ep->perst_asserted)
+		return;
+
+	ep->perst_asserted = false;
+
+	/* Enable link re-training */
+	rockchip_pcie_ep_retrain_link(rockchip);
+
+	/* Start link training */
+	schedule_delayed_work(&ep->link_training, 0);
+}
+
+static irqreturn_t rockchip_pcie_ep_perst_irq_thread(int irq, void *data)
+{
+	struct pci_epc *epc = data;
+	struct rockchip_pcie_ep *ep = epc_get_drvdata(epc);
+	struct rockchip_pcie *rockchip = &ep->rockchip;
+	u32 perst = gpiod_get_value(rockchip->perst_gpio);
+
+	if (perst)
+		rockchip_pcie_ep_perst_assert(ep);
+	else
+		rockchip_pcie_ep_perst_deassert(ep);
+
+	irq_set_irq_type(ep->perst_irq,
+			 (perst ? IRQF_TRIGGER_HIGH : IRQF_TRIGGER_LOW));
+
+	return IRQ_HANDLED;
+}
+
+static int rockchip_pcie_ep_setup_irq(struct pci_epc *epc)
+{
+	struct rockchip_pcie_ep *ep = epc_get_drvdata(epc);
+	struct rockchip_pcie *rockchip = &ep->rockchip;
+	struct device *dev = rockchip->dev;
+	int ret;
+
+	if (!rockchip->perst_gpio)
+		return 0;
+
+	/* PCIe reset interrupt */
+	ep->perst_irq = gpiod_to_irq(rockchip->perst_gpio);
+	if (ep->perst_irq < 0) {
+		dev_err(dev,
+			"failed to get IRQ for PERST# GPIO: %d\n",
+			ep->perst_irq);
+
+		return ep->perst_irq;
+	}
+
+	/*
+	 * The perst_gpio is active low, so when it is inactive on start, it
+	 * is high and will trigger the perst_irq handler. So treat this initial
+	 * IRQ as a dummy one by faking the host asserting PERST#.
+	 */
+	ep->perst_asserted = true;
+	irq_set_status_flags(ep->perst_irq, IRQ_NOAUTOEN);
+	ret = devm_request_threaded_irq(dev, ep->perst_irq, NULL,
+					rockchip_pcie_ep_perst_irq_thread,
+					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
+					"pcie-ep-perst", epc);
+	if (ret) {
+		dev_err(dev,
+			"failed to request IRQ for PERST# GPIO: %d\n",
+			ret);
+
+		return ret;
+	}
+
+	return 0;
+}
+
 static const struct pci_epc_features rockchip_pcie_epc_features = {
 	.linkup_notifier = true,
 	.msi_capable = true,
@@ -730,7 +849,7 @@ static int rockchip_pcie_ep_probe(struct platform_device *pdev)
 
 	epc = devm_pci_epc_create(dev, &rockchip_pcie_epc_ops);
 	if (IS_ERR(epc)) {
-		dev_err(dev, "failed to create epc device\n");
+		dev_err(dev, "failed to create EPC device\n");
 		return PTR_ERR(epc);
 	}
 
@@ -760,11 +879,17 @@ static int rockchip_pcie_ep_probe(struct platform_device *pdev)
 
 	pci_epc_init_notify(epc);
 
+	err = rockchip_pcie_ep_setup_irq(epc);
+	if (err < 0)
+		goto err_uninit_port;
+
 	return 0;
-err_exit_ob_mem:
-	rockchip_pcie_ep_exit_ob_mem(ep);
+err_uninit_port:
+	rockchip_pcie_deinit_phys(rockchip);
 err_disable_clocks:
 	rockchip_pcie_disable_clocks(rockchip);
+err_exit_ob_mem:
+	rockchip_pcie_ep_exit_ob_mem(ep);
 	return err;
 }
 

drivers/pci/controller/pcie-rockchip-host.c

@@ -294,7 +294,7 @@ static int rockchip_pcie_host_init_port(struct rockchip_pcie *rockchip)
 	int err, i = MAX_LANE_NUM;
 	u32 status;
 
-	gpiod_set_value_cansleep(rockchip->ep_gpio, 0);
+	gpiod_set_value_cansleep(rockchip->perst_gpio, 0);
 
 	err = rockchip_pcie_init_port(rockchip);
 	if (err)
@@ -323,7 +323,7 @@ static int rockchip_pcie_host_init_port(struct rockchip_pcie *rockchip)
 			    PCIE_CLIENT_CONFIG);
 
 	msleep(PCIE_T_PVPERL_MS);
-	gpiod_set_value_cansleep(rockchip->ep_gpio, 1);
+	gpiod_set_value_cansleep(rockchip->perst_gpio, 1);
 
 	msleep(PCIE_T_RRS_READY_MS);
 

drivers/pci/controller/pcie-rockchip.c

@@ -119,13 +119,15 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
 		return PTR_ERR(rockchip->aclk_rst);
 	}
 
-	if (rockchip->is_rc) {
-		rockchip->ep_gpio = devm_gpiod_get_optional(dev, "ep",
-							    GPIOD_OUT_LOW);
-		if (IS_ERR(rockchip->ep_gpio))
-			return dev_err_probe(dev, PTR_ERR(rockchip->ep_gpio),
-					     "failed to get ep GPIO\n");
-	}
+	if (rockchip->is_rc)
+		rockchip->perst_gpio = devm_gpiod_get_optional(dev, "ep",
+							       GPIOD_OUT_LOW);
+	else
+		rockchip->perst_gpio = devm_gpiod_get_optional(dev, "reset",
+							       GPIOD_IN);
+	if (IS_ERR(rockchip->perst_gpio))
+		return dev_err_probe(dev, PTR_ERR(rockchip->perst_gpio),
+				     "failed to get PERST# GPIO\n");
 
 	rockchip->aclk_pcie = devm_clk_get(dev, "aclk");
 	if (IS_ERR(rockchip->aclk_pcie)) {

drivers/pci/controller/pcie-rockchip.h

@@ -329,7 +329,7 @@ struct rockchip_pcie {
 	struct	regulator *vpcie3v3; /* 3.3V power supply */
 	struct	regulator *vpcie1v8; /* 1.8V power supply */
 	struct	regulator *vpcie0v9; /* 0.9V power supply */
-	struct	gpio_desc *ep_gpio;
+	struct	gpio_desc *perst_gpio;
 	u32	lanes;
 	u8      lanes_map;
 	int	link_gen;