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

[Heiko Stübner]

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 at gmail.com>
> Tested-by: Heiko Stuebner <heiko at sntech.de>
> Signed-off-by: Niklas Cassel <cassel at kernel.org>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
> Cc: stable at vger.kernel.org	# 5.15+

Reviewed-by: Heiko Stuebner <heiko at sntech.de>

it also matches what the vendor kernel does.