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Date: Fri, 17 May 2024 20:21:39 +0900
From: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Shawn Lin <shawn.lin@rock-chips.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Brian Norris <briannorris@chromium.org>, linux-pci@vger.kernel.org,
	linux-rockchip@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
	mhi@lists.linux.dev, stable@vger.kernel.org,
	Slark Xiao <slark_xiao@163.com>
Subject: Re: [PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting
 ep_gpio
Message-ID: <20240517112139.GT202520@rocinante>
References: <20240416-pci-rockchip-perst-fix-v1-1-4800b1d4d954@linaro.org>
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In-Reply-To: <20240416-pci-rockchip-perst-fix-v1-1-4800b1d4d954@linaro.org>

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