linux-kernel - [PATCH] pci: aardvark: Wait for endpoint to be ready before training link

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Date:   Wed, 13 Mar 2019 22:37:52 +0100
From:   Remi Pommarel <repk@...plefau.lt>
To:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Remi Pommarel <repk@...plefau.lt>
Subject: [PATCH] pci: aardvark: Wait for endpoint to be ready before training link

When configuring pcie reset pin from gpio (e.g. initially set by
u-boot) to pcie function this pin goes low for a brief moment
asserting the PERST# signal. Thus connected device enters fundamental
reset process and link configuration can only begin after a minimal
100ms delay (see [1]).

This makes sure that link is configured after at least 100ms from
beginning of probe() callback (shortly after the reset pin function
configuration switch through pinctrl subsytem).

[1] "PCI Express Base Specification", REV. 2.1
        PCI Express, March 4 2009, 6.6.1 Conventional Reset

Signed-off-by: Remi Pommarel <repk@...plefau.lt>
---
 drivers/pci/controller/pci-aardvark.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index a30ae7cf8e7e..70a1023d0ef1 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -177,6 +177,9 @@
 
 #define PIO_TIMEOUT_MS			1
 
+/* Endpoint can take up to 100ms to be ready after a reset */
+#define ENDPOINT_RST_MS			100
+
 #define LINK_WAIT_MAX_RETRIES		10
 #define LINK_WAIT_USLEEP_MIN		90000
 #define LINK_WAIT_USLEEP_MAX		100000
@@ -242,8 +245,10 @@ static int advk_pcie_wait_for_link(struct advk_pcie *pcie)
 	return -ETIMEDOUT;
 }
 
-static void advk_pcie_setup_hw(struct advk_pcie *pcie)
+static void
+advk_pcie_setup_hw(struct advk_pcie *pcie, unsigned long ep_rdy_time)
 {
+	unsigned long now;
 	u32 reg;
 
 	/* Set to Direct mode */
@@ -327,9 +332,12 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
 	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
 	advk_writel(pcie, reg, PIO_CTRL);
 
-	/* Start link training */
+	/* Wait for endpoint to exit reset state and start link training */
 	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
 	reg |= PCIE_CORE_LINK_TRAINING;
+	now = jiffies;
+	if (time_before(now, ep_rdy_time))
+		msleep(jiffies_to_msecs(ep_rdy_time - now));
 	advk_writel(pcie, reg, PCIE_CORE_LINK_CTRL_STAT_REG);
 
 	advk_pcie_wait_for_link(pcie);
@@ -993,8 +1001,11 @@ static int advk_pcie_probe(struct platform_device *pdev)
 	struct advk_pcie *pcie;
 	struct resource *res;
 	struct pci_host_bridge *bridge;
+	unsigned long ep_rdy_time;
 	int ret, irq;
 
+	ep_rdy_time = jiffies + msecs_to_jiffies(ENDPOINT_RST_MS);
+
 	bridge = devm_pci_alloc_host_bridge(dev, sizeof(struct advk_pcie));
 	if (!bridge)
 		return -ENOMEM;
@@ -1022,7 +1033,7 @@ static int advk_pcie_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	advk_pcie_setup_hw(pcie);
+	advk_pcie_setup_hw(pcie, ep_rdy_time);
 
 	advk_sw_pci_bridge_init(pcie);
 
-- 
2.20.1