[PATCH 1/7] PCI: imx6: Make reset-gpio optional

[Tim Harvey]

On Wed, Dec 11, 2013 at 2:30 AM, Marek Vasut <marex at denx.de> wrote:
>
> Some boards do not have a PCIe reset GPIO. To avoid probe
> failure on these boards, make the reset GPIO optional as
> well.
>
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Bjorn Helgaas <bhelgaas at google.com>
> Cc: Frank Li <lznuaa at gmail.com>
> Cc: Harro Haan <hrhaan at gmail.com>
> Cc: Jingoo Han <jg1.han at samsung.com>
> Cc: Mohit KUMAR <Mohit.KUMAR at st.com>
> Cc: Pratyush Anand <pratyush.anand at st.com>
> Cc: Richard Zhu <r65037 at freescale.com>
> Cc: Sascha Hauer <s.hauer at pengutronix.de>
> Cc: Sean Cross <xobs at kosagi.com>
> Cc: Shawn Guo <shawn.guo at linaro.org>
> Cc: Siva Reddy Kallam <siva.kallam at samsung.com>
> Cc: Srikanth T Shivanand <ts.srikanth at samsung.com>
> Cc: Tim Harvey <tharvey at gateworks.com>
> Cc: Troy Kisky <troy.kisky at boundarydevices.com>
> Cc: Yinghai Lu <yinghai at kernel.org>
> ---
>  .../devicetree/bindings/pci/designware-pcie.txt    |  2 +-
>  drivers/pci/host/pci-imx6.c                        | 29 +++++++++++-----------
>  2 files changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/pci/designware-pcie.txt b/Documentation/devicetree/bindings/pci/designware-pcie.txt
> index d5d26d4..b7a2279 100644
> --- a/Documentation/devicetree/bindings/pci/designware-pcie.txt
> +++ b/Documentation/devicetree/bindings/pci/designware-pcie.txt
> @@ -19,9 +19,9 @@ Required properties:
>         to define the mapping of the PCIe interface to interrupt
>         numbers.
>  - num-lanes: number of lanes to use
> -- reset-gpio: gpio pin number of power good signal
>
>  Optional properties for fsl,imx6q-pcie
> +- reset-gpio: gpio pin number of power good signal
>  - power-on-gpio: gpio pin number of power-enable signal
>  - wake-up-gpio: gpio pin number of incoming wakeup signal
>  - disable-gpio: gpio pin number of outgoing rfkill/endpoint disable signal
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index bd70af8..52027ad 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -214,9 +214,12 @@ static int imx6_pcie_assert_core_reset(struct pcie_port *pp)
>         regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>                         IMX6Q_GPR1_PCIE_REF_CLK_EN, 0 << 16);
>
> -       gpio_set_value(imx6_pcie->reset_gpio, 0);
> -       msleep(100);
> -       gpio_set_value(imx6_pcie->reset_gpio, 1);
> +       /* Some boards don't have PCIe reset GPIO. */
> +       if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> +               gpio_set_value(imx6_pcie->reset_gpio, 0);
> +               msleep(100);
> +               gpio_set_value(imx6_pcie->reset_gpio, 1);
> +       }
>
>         return 0;
>  }

Marek,

Though not the fault of your patch, I noticed while looking at this
that the PCI Express specification is not being properly met with
regards to PERST# and the reference clock.  The spec states that
PERST# must be kept asserted until after the reference clock is stable
(I'm not entirely clear how long of a delay is needed for the clock to
become stable but I think the value is typically the 100ms).  I see in
the current pci-imx6.c code that imx6_pcie_host_init calls
imx6_pcie_assert_core_reset first, then imx6_pcie_init_phy, followed
by imx6_pcie_deassert_core_reset.  Despite the function names,
imx6_pcie_assert_core_reset as shown above asserts then de-asserts
PERST# before the clock is enabled in imx6_pcie_deassert_core_reset.
This seems to me to be a violation of the spec and I believe the
msleep(100) and de-assertion of the option reset_gpio should be done
in imx6_pcie_deassert_core reset after the clock is brought up.

If you agree with my assessment, would you mind resolving this issue
at the same time?  If not, I'm happy to follow-up with a patch to
resolve it after your patch is accepted.

Thanks,

Tim

> @@ -439,17 +442,15 @@ static int __init imx6_pcie_probe(struct platform_device *pdev)
>
>         /* Fetch GPIOs */
>         imx6_pcie->reset_gpio = of_get_named_gpio(np, "reset-gpio", 0);
> -       if (!gpio_is_valid(imx6_pcie->reset_gpio)) {
> -               dev_err(&pdev->dev, "no reset-gpio defined\n");
> -               ret = -ENODEV;
> -       }
> -       ret = devm_gpio_request_one(&pdev->dev,
> -                               imx6_pcie->reset_gpio,
> -                               GPIOF_OUT_INIT_LOW,
> -                               "PCIe reset");
> -       if (ret) {
> -               dev_err(&pdev->dev, "unable to get reset gpio\n");
> -               goto err;
> +       if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> +               ret = devm_gpio_request_one(&pdev->dev,
> +                                       imx6_pcie->reset_gpio,
> +                                       GPIOF_OUT_INIT_LOW,
> +                                       "PCIe reset");
> +               if (ret) {
> +                       dev_err(&pdev->dev, "unable to get reset gpio\n");
> +                       goto err;
> +               }
>         }
>
>         imx6_pcie->power_on_gpio = of_get_named_gpio(np, "power-on-gpio", 0);
> --
> 1.8.4.3
>