[PATCH 6.6 426/568] PCI: dw-rockchip: Fix initial PERST# GPIO value

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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Niklas Cassel <cassel@xxxxxxxxxx>

commit 28b8d7793b8573563b3d45321376f36168d77b1e upstream.

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@xxxxxxxxxx
Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
Tested-by: Jianfeng Liu <liujianfeng1994@xxxxxxxxx>
Signed-off-by: Niklas Cassel <cassel@xxxxxxxxxx>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@xxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Heiko Stuebner <heiko@xxxxxxxxx>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx	# v5.15+
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/controller/dwc/pcie-dw-rockchip.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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(st
 		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);
 






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