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

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

On Tue, Apr 16, 2024 at 08:49:53AM +0200, Niklas Cassel wrote:
> 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>
> > ---
> 
> Reviewed-by: Niklas Cassel <cassel@kernel.org>
> 
> 
> I sent a similar fix for the DWC-based rockchip driver a few weeks ago:
> https://lore.kernel.org/linux-pci/20240327152531.814392-1-cassel@kernel.org/
> 

What a coincidence :)

> If your fix is picked up, it would be nice if mine got picked up as well,
> such that both drivers get fixed.
> 

I can see the same issue in drivers/pci/controller/dwc/pcie-histb.c but the
severity is high in that. The driver assumes that the PERST# polarity is
ACTIVE_LOW while poplar devicetree defines ACTIVE_HIGH [1]. And there is no
external polarity inversion in the PCB.

I don't know if anyone ever validated PCIe on that board. I will check
internally.

But this situation is not ideal IMO. The drivers and DTs are not consistent
w.r.t PERST# and WAKE# handling.

- Mani

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/hisilicon/hi3798cv200-poplar.dts#n182

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