Re: [PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep_gpio

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Apr 16, 2024 at 11:12:35AM +0530, Manivannan Sadhasivam wrote:
> Rockchip platforms use 'GPIO_ACTIVE_HIGH' flag in the devicetree definition
> for ep_gpio. This means, whatever the logical value set by the driver for
> the ep_gpio, physical line will output the same logic level.
> 
> For instance,
> 
> 	gpiod_set_value_cansleep(rockchip->ep_gpio, 0); --> Level low
> 	gpiod_set_value_cansleep(rockchip->ep_gpio, 1); --> Level high
> 
> But while requesting the ep_gpio, GPIOD_OUT_HIGH flag is currently used.
> Now, this also causes the physical line to output 'high' creating trouble
> for endpoint devices during host reboot.
> 
> When host reboot happens, the ep_gpio will initially output 'low' due to
> the GPIO getting reset to its POR value. Then during host controller probe,
> it will output 'high' due to GPIOD_OUT_HIGH flag. Then during
> rockchip_pcie_host_init_port(), it will first output 'low' and then 'high'
> indicating the completion of controller initialization.
> 
> On the endpoint side, each output 'low' of ep_gpio is accounted for PERST#
> assert and 'high' for PERST# deassert. With the above mentioned flow during
> host reboot, endpoint will witness below state changes for PERST#:
> 
> 	(1) PERST# assert - GPIO POR state
> 	(2) PERST# deassert - GPIOD_OUT_HIGH while requesting GPIO
> 	(3) PERST# assert - rockchip_pcie_host_init_port()
> 	(4) PERST# deassert - rockchip_pcie_host_init_port()
> 
> Now the time interval between (2) and (3) is very short as both happen
> during the driver probe(), and this results in a race in the endpoint.
> Because, before completing the PERST# deassertion in (2), endpoint got
> another PERST# assert in (3).
> 
> A proper way to fix this issue is to change the GPIOD_OUT_HIGH flag in (2)
> to GPIOD_OUT_LOW. Because the usual convention is to request the GPIO with
> a state corresponding to its 'initial/default' value and let the driver
> change the state of the GPIO when required.
> 
> As per that, the ep_gpio should be requested with GPIOD_OUT_LOW as it
> corresponds to the POR value of '0' (PERST# assert in the endpoint). Then
> the driver can change the state of the ep_gpio later in
> rockchip_pcie_host_init_port() as per the initialization sequence.
> 
> This fixes the firmware crash issue in Qcom based modems connected to
> Rockpro64 based board.
> 
> Cc:  <stable@vger.kernel.org> # 4.9
> Reported-by: Slark Xiao <slark_xiao@163.com>
> Closes: https://lore.kernel.org/mhi/20240402045647.GG2933@thinkpad/
> Fixes: e77f847df54c ("PCI: rockchip: Add Rockchip PCIe controller support")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Applied by Krzysztof to pci/controller/rockchip, but his outgoing mail
queue was broken.  Trying to squeeze it into v6.10.

> ---
>  drivers/pci/controller/pcie-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-rockchip.c b/drivers/pci/controller/pcie-rockchip.c
> index 0ef2e622d36e..c07d7129f1c7 100644
> --- a/drivers/pci/controller/pcie-rockchip.c
> +++ b/drivers/pci/controller/pcie-rockchip.c
> @@ -121,7 +121,7 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
>  
>  	if (rockchip->is_rc) {
>  		rockchip->ep_gpio = devm_gpiod_get_optional(dev, "ep",
> -							    GPIOD_OUT_HIGH);
> +							    GPIOD_OUT_LOW);
>  		if (IS_ERR(rockchip->ep_gpio))
>  			return dev_err_probe(dev, PTR_ERR(rockchip->ep_gpio),
>  					     "failed to get ep GPIO\n");
> 
> ---
> base-commit: 4cece764965020c22cff7665b18a012006359095
> change-id: 20240416-pci-rockchip-perst-fix-88c922621d9a
> 
> Best regards,
> -- 
> Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>