linux-kernel - Re: [PATCH v6 2/4] mmc: core: Add MMC_POWEROFF_UNDERVOLTAGE support in _mmc

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Message-ID: <CAPDyKFp1gyJYWpuHB2-fP2q9ZuRwHNMJAB_0rPScYvD6rPi8wQ@mail.gmail.com>
Date: Fri, 4 Jul 2025 14:50:43 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>, Avri Altman <avri.altman@...disk.com>
Cc: kernel@...gutronix.de, linux-kernel@...r.kernel.org, 
	linux-mmc@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Mark Brown <broonie@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Søren Andersen <san@...v.dk>, 
	Christian Loehle <christian.loehle@....com>, Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v6 2/4] mmc: core: Add MMC_POWEROFF_UNDERVOLTAGE support
 in _mmc_suspend()

On Mon, 16 Jun 2025 at 12:29, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>
> Introduce MMC_POWEROFF_UNDERVOLTAGE as a new mmc_poweroff_type value and
> adjust _mmc_suspend() to skip cache flush for this case. This prepares for
> undervoltage handling in a follow-up patch.
>
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> ---
> changes v5:
> - rebase against latest mmc/next
> - use MMC_POWEROFF_UNDERVOLTAGE enum instead of function parameter.
> changes v3:
> - add comments
> - make sure _mmc_flush_cache is not executed in the undervoltage case
> ---
>  drivers/mmc/core/mmc.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 5689ab6eefe1..6812df679ba9 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -36,6 +36,7 @@
>  enum mmc_poweroff_type {
>         MMC_POWEROFF_SUSPEND,
>         MMC_POWEROFF_SHUTDOWN,
> +       MMC_POWEROFF_UNDERVOLTAGE,
>         MMC_POWEROFF_UNBIND,
>  };
>
> @@ -2132,9 +2133,15 @@ static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
>         if (mmc_card_suspended(host->card))
>                 goto out;
>
> -       err = _mmc_flush_cache(host);
> -       if (err)
> -               goto out;
> +       /*
> +        * For the undervoltage case, we care more about device integrity.
> +        * Avoid cache flush and notify the device to power off quickly.
> +        */
> +       if (pm_type != MMC_POWEROFF_UNDERVOLTAGE) {
> +               err = _mmc_flush_cache(host);
> +               if (err)
> +                       goto out;
> +       }

I think this sounds reasonable as we may simply not have the time to
complete a flush.

Yet, it may be device specific on what makes best sense. Let's see if
Avri also agrees with this.

>
>         if (mmc_card_can_poweroff_notify(host->card) &&
>             mmc_host_can_poweroff_notify(host, pm_type))
> --
> 2.39.5
>

That said, please squash this with patch3. Especially since I think
patch3 can be made a bit simpler due to my comments on patch1.

Kind regards
Uffe