Hello,
> 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.
Applied to controller/rockchip, thank you!
[1/1] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep_gpio
https://git.kernel.org/pci/pci/c/fa562e9441e3
Krzysztof
