On Tue, Apr 16, 2024 at 02:15:22PM +0200, Niklas Cassel wrote:
> PERST is active low according to the PCIe specification.
Maybe update the subject to mention that this is about PERST# and
avoiding an unnecessary toggle.
Also maybe worth using "PERST#" here in the commit log to match the
spec and connect with the explicit GPIO levels.
> 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")
> Tested-by: Jianfeng Liu <liujianfeng1994@xxxxxxxxx>
> Signed-off-by: Niklas Cassel <cassel@xxxxxxxxxx>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 5.15+
> ---
> Changes since V1:
> -Picked up tags.
> -CC stable.
> -Clarified commit message.
>
> 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
>
