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

Remi Pommarel
2019-03-13T21:29:38Z

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@triplefau.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