PCI: dw-rockchip: Fix initial PERST# GPIO valuecontroller/rockchip

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!

This extra, very short, PERST# assertion + deassertion has been reported
to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Link: https://lore.kernel.org/linux-pci/20240417164227.398901-1-cassel@kernel.org
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Jianfeng Liu <liujianfeng1994@gmail.com>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: <stable@vger.kernel.org>	# 5.15+

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index a13ca83ce26094..61b1acba7182ed 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -245,7 +245,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev,
 				     "failed to map apb registers\n");
 
 	rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
-						     GPIOD_OUT_HIGH);
+						     GPIOD_OUT_LOW);
 	if (IS_ERR(rockchip->rst_gpio))
 		return dev_err_probe(&pdev->dev, PTR_ERR(rockchip->rst_gpio),
 				     "failed to get reset gpio\n");