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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Mar 27, 2024 at 04:25:31PM +0100, Niklas Cassel wrote:
> 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.

There is no 'core' here, are you referring to the device?

> (E.g. if the bootloader would leave PERST deasserted.)
> 

I don't follow this last sentence. But even without that, the commit message
itself is descriptive enough.

> Signed-off-by: Niklas Cassel <cassel@kernel.org>

This is a legitimate bug fix. So you should add the fixes tag and CC stable to
get it backported.

But the patch itself looks fine to me.

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

- Mani

> ---
>  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
> 
> 

-- 
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