On Wed, Mar 27, 2024 at 04:25:31PM +0100, 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! > > Without this change, there is no guarantee that PERST will be asserted > while the core is performing a fundamental reset. There is no 'core' here, are you referring to the device? > (E.g. if the bootloader would leave PERST deasserted.) > I don't follow this last sentence. But even without that, the commit message itself is descriptive enough. > Signed-off-by: Niklas Cassel <cassel@xxxxxxxxxx> This is a legitimate bug fix. So you should add the fixes tag and CC stable to get it backported. But the patch itself looks fine to me. Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> - Mani > --- > 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); > if (IS_ERR(rockchip->rst_gpio)) > return PTR_ERR(rockchip->rst_gpio); > > -- > 2.44.0 > > -- மணிவண்ணன் சதாசிவம்
