linux-kernel - Re: [PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep

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Date: Tue, 16 Apr 2024 08:49:53 +0200
From: Niklas Cassel <cassel@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Shawn Lin <shawn.lin@...k-chips.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Brian Norris <briannorris@...omium.org>, linux-pci@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mhi@...ts.linux.dev, stable@...r.kernel.org,
	Slark Xiao <slark_xiao@....com>
Subject: Re: [PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting
 ep_gpio

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@...r.kernel.org> # 4.9
> Reported-by: Slark Xiao <slark_xiao@....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@...aro.org>
> ---

Reviewed-by: Niklas Cassel <cassel@...nel.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/

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


Kind regards,
Niklas