From: "Heiko Stübner" <heiko@sntech.de>
To: "Lorenzo Pieralisi" <lpieralisi@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Rob Herring" <robh@kernel.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Simon Xue" <xxm@rock-chips.com>,
"Kever Yang" <kever.yang@rock-chips.com>,
"Niklas Cassel" <cassel@kernel.org>
Cc: Damien Le Moal <dlemoal@kernel.org>,
Niklas Cassel <cassel@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: Tue, 30 Apr 2024 10:38:09 +0200 [thread overview]
Message-ID: <2493811.Mh6RI2rZIc@diego> (raw)
In-Reply-To: <20240417164227.398901-1-cassel@kernel.org>
Am Mittwoch, 17. April 2024, 18:42:26 CEST schrieb Niklas Cassel:
> 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.
>
> Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
> Tested-by: Jianfeng Liu <liujianfeng1994@gmail.com>
> Tested-by: Heiko Stuebner <heiko@sntech.de>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Cc: stable@vger.kernel.org # 5.15+
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
it also matches what the vendor kernel does.
next prev parent reply other threads:[~2024-04-30 8:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-17 16:42 [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value Niklas Cassel
2024-04-30 8:38 ` Heiko Stübner [this message]
2024-05-15 21:20 ` Bjorn Helgaas
2024-05-17 11:22 ` Krzysztof Wilczyński
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