On Wed, Apr 17, 2024 at 06:42:26PM +0200, Niklas Cassel wrote:
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+
Applied by Krzysztof to pci/controller/rockchip. His outgoing mail queue was stuck, but I'm trying to squeeze this into v6.10.
Changes since v2: -Picked up tag from Heiko. -Change subject (Bjorn). -s/PERST/PERST#/ (Bjorn).
drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c index d6842141d384..a909e42b4273 100644 --- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c +++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c @@ -240,7 +240,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev, return PTR_ERR(rockchip->apb_base); rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
GPIOD_OUT_HIGH);
GPIOD_OUT_LOW);2.44.0