Re: [PATCH v11 6/6] mmc: core: Add support for resetting an eMMC at system resume

[Ulf Hansson]

On Fri, Oct 30, 2026 at 7:11 PM Kamal Dasu <kamal.dasu@xxxxxxxxxxxx> wrote:
>
> From: Ulf Hansson <ulf.hansson@xxxxxxxxxxxxxxxx>
>
> The DT property reset-card-at-resume specifies that we need to make a reset
> of an eMMC card at system resume, assuming it also has stayed powered on
> during system suspend.
>
> To implement support for this, let's start by parsing for the new DT
> property and set the new bit MMC_CAP2_RESET_AT_RESUME if it's found. Based
> on the property, we must also set MMC_PM_KEEP_POWER in the pm_flags for the
> host, to keep the eMMC powered on during system suspend.
>
> Finally, to manage the actual reset during system resume, let's extend
> mmc_resume() to support the needed behaviour.
>
> The property only makes sense together with keep-power-in-suspend, as the
> card would otherwise be powered off and system suspend is refused. Warn
> about that while parsing the DT properties, to flag the misconfiguration
> upfront. While at it, claim the host around the reset in mmc_resume(), as
> it sends commands to the card.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxxxxxxxx>
> Co-developed-by: Kamal Dasu <kamal.dasu@xxxxxxxxxxxx>
> Signed-off-by: Kamal Dasu <kamal.dasu@xxxxxxxxxxxx>
> ---
>  drivers/mmc/core/host.c  | 13 +++++++++++++
>  drivers/mmc/core/mmc.c   |  8 ++++++++
>  include/linux/mmc/host.h |  1 +
>  3 files changed, 22 insertions(+)
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index 8e9e61839198..8b38ff45d20f 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -48,6 +48,14 @@ static int mmc_host_class_prepare(struct device *dev)
>         if (host->bus_ops->pre_suspend)
>                 return host->bus_ops->pre_suspend(host);
>
> +       /*
> +        * If it's required to make a reset of the card at system resume, this
> +        * indirectly also means that we must keep the card powered on during
> +        * system suspend.
> +        */
> +       if (host->caps2 & MMC_CAP2_RESET_AT_RESUME)
> +               return mmc_set_host_pm_flags(host, MMC_PM_KEEP_POWER);
> +
>         return 0;
>  }
>
> @@ -375,6 +383,11 @@ int mmc_of_parse(struct mmc_host *host)
>                 host->pm_caps |= MMC_PM_KEEP_POWER;
>         if (device_property_read_bool(dev, "wakeup-source"))
>                 host->pm_caps |= MMC_PM_WAKE_SDIO_IRQ;
> +       if (device_property_read_bool(dev, "reset-card-at-resume")) {
> +               host->caps2 |= MMC_CAP2_RESET_AT_RESUME;
> +               if (!(host->pm_caps & MMC_PM_KEEP_POWER))
> +                       dev_warn(dev, "reset-card-at-resume without keep-power-in-suspend, system suspend will fail\n");

I think it's better to check this in mmc_validate_host_caps(). In this
way, we will make the host driver probe to fail if there is
misconfiguration.

> +       }
>         if (device_property_read_bool(dev, "mmc-ddr-3_3v"))
>                 host->caps |= MMC_CAP_3_3V_DDR;
>         if (device_property_read_bool(dev, "mmc-ddr-1_8v"))
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 026003ba507d..a9e3cf7ae039 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -2320,6 +2320,14 @@ static int mmc_resume(struct mmc_host *host)
>         }
>
>         pm_runtime_enable(&host->card->dev);
> +
> +       if (mmc_card_keep_power(host) &&
> +           host->caps2 & MMC_CAP2_RESET_AT_RESUME) {
> +               mmc_claim_host(host);
> +               _mmc_hw_reset(host);
> +               mmc_release_host(host);
> +       }
> +
>         host->pm_flags &= ~MMC_PM_KEEP_POWER;
>         return 0;
>  }
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 032c018650e0..3c0ea74e3e35 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -430,6 +430,7 @@ struct mmc_host {
>         u32                     caps2;          /* More host capabilities */
>
>  #define MMC_CAP2_BOOTPART_NOACC        (1 << 0)        /* Boot partition no access */
> +#define MMC_CAP2_RESET_AT_RESUME BIT(1)        /* Reset the card at system resume */
>  #define MMC_CAP2_FULL_PWR_CYCLE        (1 << 2)        /* Can do full power cycle */
>  #define MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND (1 << 3) /* Can do full power cycle in suspend */
>  #define MMC_CAP2_HS200_1_8V_SDR        (1 << 5)        /* can support */
> --
> 2.34.1
>

Other than the above, this looks good to me!

Kind regards
Uffe