Re: [PATCH v2 3/3] mmc: core: Add power-off-delay-us support

[Ulf Hansson]

On Wed, Jul 22, 2026 at 10:57 PM Judith Mendez <jm@xxxxxx> wrote:
>
> Add support for power-off-delay-us which shall be used to specify
> value of delay after deasserting power during MMC power cycles.
> Default for delay is 1000us but custom delay can be passed in to work
> around hardware issues such as slow RC discharge on MMC VDD rails.
>
> Signed-off-by: Judith Mendez <jm@xxxxxx>
> ---
> Changes since v1:
> - Move delay to mmc_power_off
> - Fix dt checks and remove print
> - Move from mmc_host struct to mmc_ios struct
> - Rename post-power-off-delay-ms to power_off_delay_us
> ---
>  drivers/mmc/core/core.c  | 2 +-
>  drivers/mmc/core/host.c  | 8 ++++++++
>  include/linux/mmc/host.h | 1 +
>  3 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 29e80e5f928e9..9472041fe1c20 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1388,7 +1388,7 @@ void mmc_power_off(struct mmc_host *host)
>          * XO-1.5, require a short delay after poweroff before the card
>          * can be successfully turned on again.
>          */
> -       mmc_delay(1);
> +       mmc_delay_us(host->ios.power_off_delay_us);
>  }
>
>  void mmc_power_cycle(struct mmc_host *host, u32 ocr)
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index b7ce3137d4529..fac50a2860211 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -421,6 +421,13 @@ int mmc_of_parse(struct mmc_host *host)
>         device_property_read_u32(dev, "post-power-on-delay-ms",
>                                  &host->ios.power_delay_ms);
>
> +       device_property_read_u32(dev, "power-off-delay-us",
> +                                &host->ios.power_off_delay_us);
> +       if (host->ios.power_off_delay_us < 1)
> +               host->ios.power_off_delay_us = 1000;

If power-off-delay-us is specified and the value >= 0, I think we can
respect it as is.

This means we need to treat "0" a bit special and bail out in mmc_delay_us().

> +       if (host->ios.power_off_delay_us > 10000000)
> +               host->ios.power_off_delay_us = 10000000;
> +
>         return mmc_pwrseq_alloc(host);
>  }
>
> @@ -574,6 +581,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
>
>         host->fixed_drv_type = -EINVAL;
>         host->ios.power_delay_ms = 10;
> +       host->ios.power_off_delay_us = 1000;
>         host->ios.power_mode = MMC_POWER_UNDEFINED;
>
>         return host;
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index ba84f02c2a101..714417466707c 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -23,6 +23,7 @@ struct mmc_ios {
>         unsigned int    clock;                  /* clock rate */
>         unsigned short  vdd;
>         unsigned int    power_delay_ms;         /* waiting for stable power */
> +       unsigned int    power_off_delay_us;     /* waiting for power discharge */
>
>  /* vdd stores the bit number of the selected voltage range from below. */
>
> --
> 2.54.0
>

Kind regards
Uffe