On Monday 31 May 2021 11:05:40 Luca Ceresoli wrote:
> The PCIe PERSTn reset pin is active low and should be asserted, then
> deasserted.
>
> The current implementation only drives the pin once in "HIGH" position,
> thus presumably it was intended to deassert the pin. This has two problems:
>
> 1) it assumes the pin was asserted by other means before loading the
> driver
> 2) it has the wrong polarity, since "HIGH" means "active", and the pin is
> presumably configured as active low coherently with the PCIe
> convention, thus it is driven physically to 0, keeping the device
> under reset unless the pin is configured as active high.
>
> Fix both problems by:
>
> 1) keeping devm_gpiod_get_optional(dev, NULL, GPIOD_OUT_HIGH) as is, but
> assuming the pin is correctly configured as "active low" this now
> becomes a reset assertion
> 2) adding gpiod_set_value(reset, 0) after a delay to deassert reset
>
> Fixes: 78bdcad05ea1 ("PCI: dra7xx: Add support to make GPIO drive PERST# line")
> Signed-off-by: Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>
>
> ---
>
> Changes v1 -> v2:
> - No changes to the patch
> - Reword commit message according to suggestions from Bjorn Helgaas (from
> another patchset)
> - Add Fixes: tag
> ---
> drivers/pci/controller/dwc/pci-dra7xx.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
> index cb5d4c245ff6..11f392b7a9a2 100644
> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
> @@ -801,6 +801,8 @@ static int dra7xx_pcie_probe(struct platform_device *pdev)
> dev_err(&pdev->dev, "gpio request failed, ret %d\n", ret);
> goto err_gpio;
> }
> + usleep_range(1000, 2000);
Hello! Just a note that this is again a new code pattern in another
driver for different wait value of PCIe Warm Reset timeout. I sent email
about these issues:
https://lore.kernel.org/linux-pci/20210310110535.zh4pnn4vpmvzwl5q@pali/
Luca, how did you choose value 1000-2000 us? Do you have some reference
or specification which says that this value needs to be used?
> + gpiod_set_value(reset, 0);
>
> reg = dra7xx_pcie_readl(dra7xx, PCIECTRL_DRA7XX_CONF_DEVICE_CMD);
> reg &= ~LTSSM_EN;
> --
> 2.25.1
>
