Re: [PATCH v3 05/12] PCI: aardvark: Issue PERST via GPIO

[Rob Herring <robh@kernel.org>]

On Fri, Apr 24, 2020 at 10:39 AM Pali Rohár <pali@kernel.org> wrote:
>
> Add support for issuing PERST via GPIO specified in 'reset-gpios'
> property (as described in PCI device tree bindings).
>
> Some buggy cards (e.g. Compex WLE900VX or WLE1216) are not detected
> after reboot when PERST is not issued during driver initialization.
>
> If bootloader already enabled link training then issuing PERST has no
> effect for some buggy cards (e.g. Compex WLE900VX) and these cards are
> not detected. We therefore clear the LINK_TRAINING_EN register before.
>
> It was observed that Compex WLE900VX card needs to be in PERST reset
> for at least 10ms if bootloader enabled link training.
>
> Tested on Turris MOX.
>
> Signed-off-by: Pali Rohár <pali@kernel.org>
> ---
>  drivers/pci/controller/pci-aardvark.c | 43 ++++++++++++++++++++++++++-
>  1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index a6c4d4d52631..9e2f44213b5e 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -9,6 +9,7 @@
>   */
>
>  #include <linux/delay.h>
> +#include <linux/gpio.h>
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
>  #include <linux/irqdomain.h>
> @@ -18,6 +19,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/msi.h>
>  #include <linux/of_address.h>
> +#include <linux/of_gpio.h>
>  #include <linux/of_pci.h>
>
>  #include "../pci.h"
> @@ -204,6 +206,7 @@ struct advk_pcie {
>         int root_bus_nr;
>         int link_gen;
>         struct pci_bridge_emul bridge;
> +       struct gpio_desc *reset_gpio;
>  };
>
>  static inline void advk_writel(struct advk_pcie *pcie, u32 val, u64 reg)
> @@ -330,10 +333,31 @@ static void advk_pcie_train_link(struct advk_pcie *pcie)
>         dev_err(dev, "link never came up\n");
>  }
>
> +static void advk_pcie_issue_perst(struct advk_pcie *pcie)
> +{
> +       u32 reg;
> +
> +       if (!pcie->reset_gpio)
> +               return;
> +
> +       /* PERST does not work for some cards when link training is enabled */
> +       reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG);
> +       reg &= ~LINK_TRAINING_EN;
> +       advk_writel(pcie, reg, PCIE_CORE_CTRL0_REG);
> +
> +       /* 10ms delay is needed for some cards */
> +       dev_info(&pcie->pdev->dev, "issuing PERST via reset GPIO for 10ms\n");
> +       gpiod_set_value_cansleep(pcie->reset_gpio, 1);
> +       usleep_range(10000, 11000);
> +       gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> +}
> +
>  static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  {
>         u32 reg;
>
> +       advk_pcie_issue_perst(pcie);
> +
>         /* Set to Direct mode */
>         reg = advk_readl(pcie, CTRL_CONFIG_REG);
>         reg &= ~(CTRL_MODE_MASK << CTRL_MODE_SHIFT);
> @@ -406,7 +430,8 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>
>         /*
>          * PERST# signal could have been asserted by pinctrl subsystem before
> -        * probe() callback has been called, making the endpoint going into
> +        * probe() callback has been called or issued explicitly by reset gpio
> +        * function advk_pcie_issue_perst(), making the endpoint going into
>          * fundamental reset. As required by PCI Express spec a delay for at
>          * least 100ms after such a reset before link training is needed.
>          */
> @@ -1046,6 +1071,22 @@ static int advk_pcie_probe(struct platform_device *pdev)
>         }
>         pcie->root_bus_nr = bus->start;
>
> +       pcie->reset_gpio = devm_gpiod_get_from_of_node(dev, dev->of_node,
> +                                                      "reset-gpios", 0,
> +                                                      GPIOD_OUT_LOW,
> +                                                      "pcie1-reset");
> +       ret = PTR_ERR_OR_ZERO(pcie->reset_gpio);
> +       if (ret) {
> +               if (ret == -ENOENT) {
> +                       pcie->reset_gpio = NULL;
> +               } else {
> +                       if (ret != -EPROBE_DEFER)
> +                               dev_err(dev, "Failed to get reset-gpio: %i\n",
> +                                       ret);
> +                       return ret;
> +               }
> +       }

I believe all this can be replaced with devm_gpiod_get_optional.

Rob