Re: [PATCH 2/2] mmc: core: Add post-power-off-delay-ms support

On Fri, Jul 17, 2026 at 1:26 AM Judith Mendez <[email protected]> wrote:
>
> Add support for post-power-off-delay-ms which shall be used to insert
> a configurable delay post MMC power off.
>
> Signed-off-by: Judith Mendez <[email protected]>
> ---
>  drivers/mmc/core/core.c  | 8 ++++++--
>  drivers/mmc/core/host.c  | 8 ++++++++
>  include/linux/mmc/host.h | 1 +
>  3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 29e80e5f928e9..f9049aaf44394 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1394,8 +1394,12 @@ void mmc_power_off(struct mmc_host *host)
>  void mmc_power_cycle(struct mmc_host *host, u32 ocr)
>  {
>         mmc_power_off(host);
> -       /* Wait at least 1 ms according to SD spec */
> -       mmc_delay(1);

The above delay is kind of questionable in the first place, as we
already have a mmc_delay(1) at the end of mmc_power_off().

Maybe the delay is needed for legacy reasons and because of that, I
would suggest that we leave mmc_power_cycle() as is, for now. In the
end, I would rather see that the above delay gets removed altogether.

Instead, how about making the mmc_delay(1) in mmc_power_off() configurable?

Moreover, rather than the code below, I think it would be better to
set a default value for "host->post_power_off_delay_ms" to 1 in
mmc_alloc_host(). In fact, there is already similar code for
"host->ios.power_delay_ms", please try to follow that for this case
too.

> +       if (host->post_power_off_delay_ms) {
> +               mmc_delay(host->post_power_off_delay_ms);
> +       } else {
> +               /* Wait at least 1 ms according to SD spec */
> +               mmc_delay(1);
> +       }
>         mmc_power_up(host, ocr);
>  }
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index b7ce3137d4529..ea8f36827e41c 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -421,6 +421,14 @@ 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, "post-power-off-delay-ms",
> +                                &host->post_power_off_delay_ms);
> +       if (host->post_power_off_delay_ms > 10000) {
> +               dev_err(dev, "post-power-off-delay-ms %u exceeds max 10000, setting 10000\n",
> +                       host->post_power_off_delay_ms);
> +               host->post_power_off_delay_ms = 10000;
> +       }
> +
>         return mmc_pwrseq_alloc(host);
>  }
>
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index ba84f02c2a101..b751b61b1116e 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -578,6 +578,7 @@ struct mmc_host {
>
>         u32                     err_stats[MMC_ERR_MAX];
>         u32                     max_sd_hs_hz;
> +       u32                     post_power_off_delay_ms;
>         unsigned long           private[] ____cacheline_aligned;
>  };
>
> --
> 2.54.0
>

Kind regards
Uffe