[PATCH 4.14 034/106] PCI: aardvark: Wait for endpoint to be ready before training link

Greg Kroah-Hartman
2021-12-06T15:08:32Z

From: Remi Pommarel <repk@triplefau.lt>

commit f4c7d053d7f77cd5c1a1ba7c7ce085ddba13d1d7 upstream.

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]).

Because the pin configuration comes from the "default" pinctrl it is
implicitly configured before the probe callback is called:

driver_probe_device()
really_probe()
...
pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
function and PERST# is asserted */
...
drv->probe()

[1] "PCI Express Base Specification", REV. 4.0
PCI Express, February 19 2014, 6.6.1 Conventional Reset

Signed-off-by: Remi Pommarel <repk@triplefau.lt>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/pci/host/pci-aardvark.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/drivers/pci/host/pci-aardvark.c
+++ b/drivers/pci/host/pci-aardvark.c
@@ -362,6 +362,14 @@ static void advk_pcie_setup_hw(struct ad
reg |= PIO_CTRL_ADDR_WIN_DISABLE;
advk_writel(pcie, reg, PIO_CTRL);

+ /*
+ * PERST# signal could have been asserted by pinctrl subsystem before
+ * probe() callback has been called, making the endpoint going into
+ * fundamental reset. As required by PCI Express spec a delay for at
+ * least 100ms after such a reset before link training is needed.
+ */
+ msleep(PCI_PM_D3COLD_WAIT);
+
/* Start link training */
reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
reg |= PCIE_CORE_LINK_TRAINING;