Re: [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

From: "Krzysztof Wilczyński" <kw@linux.com>
To: Niklas Cassel <cassel@kernel.org>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Rob Herring <robh@kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Heiko Stuebner <heiko@sntech.de>, Simon Xue <xxm@rock-chips.com>,
	Kever Yang <kever.yang@rock-chips.com>,
	Damien Le Moal <dlemoal@kernel.org>,
	Jianfeng Liu <liujianfeng1994@gmail.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	stable@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org
Subject: Re: [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value
Date: Fri, 17 May 2024 20:22:39 +0900	[thread overview]
Message-ID: <20240517112239.GU202520@rocinante> (raw)
In-Reply-To: <20240417164227.398901-1-cassel@kernel.org>

Hello,

> PERST# is active low according to the PCIe specification.
> 
> However, the existing pcie-dw-rockchip.c driver does:
> gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1);
> When asserting + deasserting PERST#.
> 
> This is of course wrong, but because all the device trees for this
> compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
> $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
> $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
> 
> The actual toggling of PERST# is correct.
> (And we cannot change it anyway, since that would break device tree
> compatibility.)
> 
> However, this driver does request the GPIO to be initialized as
> GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets
> toggled back and forth for no good reason.
> 
> Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW
> (which for this driver means PERST# asserted).
> 
> This will avoid an unnecessary signal change where PERST# gets deasserted
> (by devm_gpiod_get_optional()) and then gets asserted
> (by rockchip_pcie_start_link()) just a few instructions later.
> 
> Before patch, debug prints on EP side, when booting RC:
> [  845.606810] pci: PERST# asserted by host!
> [  852.483985] pci: PERST# de-asserted by host!
> [  852.503041] pci: PERST# asserted by host!
> [  852.610318] pci: PERST# de-asserted by host!
> 
> After patch, debug prints on EP side, when booting RC:
> [  125.107921] pci: PERST# asserted by host!
> [  132.111429] pci: PERST# de-asserted by host!
> 
> This extra, very short, PERST# assertion + deassertion has been reported
> to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Applied to controller/rockchip, thank you!

[1/1] PCI: dw-rockchip: Fix initial PERST# GPIO value
      https://git.kernel.org/pci/pci/c/b00c483a1075

	Krzysztof

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