[PATCH V4 4/4] mmc: pwrseq_simple: Add support for a reset GPIO pin

[Alexandre Courbot]

On Mon, Jan 19, 2015 at 6:13 PM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
> The need for reset GPIOs has several times been pointed out from
> erlier posted patchsets. Especially some WLAN chips which are
> attached to an SDIO interface may use a GPIO reset.
>
> The reset GPIO is asserted at initialization and prior we start the
> power up procedure. The GPIO will be de-asserted right after the power
> has been provided to the card, from the ->post_power_on() callback.
>
> Note, the reset GPIO is optional. Thus we don't return an error even if
> we can't find a GPIO for the consumer.
>
> Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>

Excellent, with this I can probe the wifi chip on NVIDIA SHIELD which
requires a GPIO to be high for reset to be de-asserted.

The series:

Tested-by: Alexandre Courbot <acourbot at nvidia.com>

> ---
>
> Changes in v4:
>         - Fixed call to kfree().
>
> ---
>  drivers/mmc/core/pwrseq_simple.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
>
> diff --git a/drivers/mmc/core/pwrseq_simple.c b/drivers/mmc/core/pwrseq_simple.c
> index 61c991e..0958c69 100644
> --- a/drivers/mmc/core/pwrseq_simple.c
> +++ b/drivers/mmc/core/pwrseq_simple.c
> @@ -11,6 +11,7 @@
>  #include <linux/slab.h>
>  #include <linux/device.h>
>  #include <linux/err.h>
> +#include <linux/gpio/consumer.h>
>
>  #include <linux/mmc/host.h>
>
> @@ -18,31 +19,68 @@
>
>  struct mmc_pwrseq_simple {
>         struct mmc_pwrseq pwrseq;
> +       struct gpio_desc *reset_gpio;
>  };
>
> +static void mmc_pwrseq_simple_pre_power_on(struct mmc_host *host)
> +{
> +       struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
> +                                       struct mmc_pwrseq_simple, pwrseq);
> +
> +       if (!IS_ERR(pwrseq->reset_gpio))
> +               gpiod_set_value_cansleep(pwrseq->reset_gpio, 1);
> +}
> +
> +static void mmc_pwrseq_simple_post_power_on(struct mmc_host *host)
> +{
> +       struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
> +                                       struct mmc_pwrseq_simple, pwrseq);
> +
> +       if (!IS_ERR(pwrseq->reset_gpio))
> +               gpiod_set_value_cansleep(pwrseq->reset_gpio, 0);
> +}
> +
>  static void mmc_pwrseq_simple_free(struct mmc_host *host)
>  {
>         struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
>                                         struct mmc_pwrseq_simple, pwrseq);
>
> +       if (!IS_ERR(pwrseq->reset_gpio))
> +               gpiod_put(pwrseq->reset_gpio);
> +
>         kfree(pwrseq);
>         host->pwrseq = NULL;
>  }
>
>  static struct mmc_pwrseq_ops mmc_pwrseq_simple_ops = {
> +       .pre_power_on = mmc_pwrseq_simple_pre_power_on,
> +       .post_power_on = mmc_pwrseq_simple_post_power_on,
> +       .power_off = mmc_pwrseq_simple_pre_power_on,
>         .free = mmc_pwrseq_simple_free,
>  };
>
>  int mmc_pwrseq_simple_alloc(struct mmc_host *host, struct device *dev)
>  {
>         struct mmc_pwrseq_simple *pwrseq;
> +       int ret = 0;
>
>         pwrseq = kzalloc(sizeof(struct mmc_pwrseq_simple), GFP_KERNEL);
>         if (!pwrseq)
>                 return -ENOMEM;
>
> +       pwrseq->reset_gpio = gpiod_get_index(dev, "reset", 0, GPIOD_OUT_HIGH);

gpiod_get() will translate to exactly the same, with less characters.

Actually I see that the version in -next has support for multiple
GPIOs. You will probably want to look at Rojhalat's latest work on
GPIO arrays:

http://permalink.gmane.org/gmane.linux.kernel.gpio/6126

This code would be a great candidate to use this GPIO array API, but
since it is not in -next yet (should happen soon though) you might
want to consider doing it later.

Btw, I wasted a considerable amount of time on one of the defunct
previous attempts at power sequences, so I'm interested in reviewing
future versions of this patchset if you don't mind adding me to the CC
list. :)