[PATCH] PCI: dw-rockchip: Fix GPIO initialization flag

[Niklas Cassel]

PERST is active low according to the PCIe specification.

However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1);
When asserting + deasserting PERST.

This is of course wrong, but because all the device trees for this
compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*

The actual toggling of PERST is correct.
(And we cannot change it anyway, since that would break device tree
compatibility.)

However, this driver does request the GPIO to be initialized as
GPIOD_OUT_HIGH, which does cause a silly sequence where PERST gets
toggled back and forth for no good reason.

Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW
(which for this driver means PERST asserted).

This will avoid an unnecessary signal change where PERST gets deasserted
(by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.

Before patch, debug prints on EP side, when booting RC:
[  845.606810] pci: PERST asserted by host!
[  852.483985] pci: PERST de-asserted by host!
[  852.503041] pci: PERST asserted by host!
[  852.610318] pci: PERST de-asserted by host!

After patch, debug prints on EP side, when booting RC:
[  125.107921] pci: PERST asserted by host!
[  132.111429] pci: PERST de-asserted by host!

Without this change, there is no guarantee that PERST will be asserted
while the core is performing a fundamental reset.
(E.g. if the bootloader would leave PERST deasserted.)

Signed-off-by: Niklas Cassel <cassel at kernel.org>
---
 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index d6842141d384..a909e42b4273 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -240,7 +240,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev,
 		return PTR_ERR(rockchip->apb_base);
 
 	rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
-						     GPIOD_OUT_HIGH);
+						     GPIOD_OUT_LOW);
 	if (IS_ERR(rockchip->rst_gpio))
 		return PTR_ERR(rockchip->rst_gpio);
 
-- 
2.44.0