[2/5] mmc: core: Further avoid re-storing power to the eMMC before a shutdown

To manage a graceful power-off of the eMMC card during platform shutdown,
the preferred option is to use the poweroff-notification command.

Due to an earlier suspend request the eMMC may already have been properly
powered-off, hence we are sometimes leaving the eMMC in its current state.
However, in one case when the host has MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND
set we may unnecessarily restore the power to the eMMC, let's avoid this.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/mmc/core/mmc.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

> To manage a graceful power-off of the eMMC card during platform shutdown,
> the preferred option is to use the poweroff-notification command.
> 
> Due to an earlier suspend request the eMMC may already have been properly
> powered-off, hence we are sometimes leaving the eMMC in its current state.
> However, in one case when the host has
> MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND
> set we may unnecessarily restore the power to the eMMC, let's avoid this.
> 
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>  drivers/mmc/core/mmc.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c index
> 3424bc9e20c5..400dd0449fec 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -2014,6 +2014,18 @@ static bool mmc_can_poweroff_notify(const
> struct mmc_card *card)
>  		(card->ext_csd.power_off_notification ==
> EXT_CSD_POWER_ON);  }
> 
> +static bool mmc_may_poweroff_notify(const struct mmc_host *host,
> +				    bool is_suspend)
> +{
> +	if (host->caps2 & MMC_CAP2_FULL_PWR_CYCLE)
> +		return true;
> +
> +	if (host->caps2 & MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND &&
> is_suspend)
> +		return true;
> +
> +	return !is_suspend;
> +}
> +
>  static int mmc_poweroff_notify(struct mmc_card *card, unsigned int
> notify_type)  {
>  	unsigned int timeout = card->ext_csd.generic_cmd6_time; @@ -
> 2124,8 +2136,7 @@ static int _mmc_suspend(struct mmc_host *host, bool
> is_suspend)
>  		goto out;
> 
>  	if (mmc_can_poweroff_notify(host->card) &&
> -	    ((host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) || !is_suspend ||
> -	     (host->caps2 & MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND)))
> +	    mmc_may_poweroff_notify(host, is_suspend))
>  		err = mmc_poweroff_notify(host->card, notify_type);
>  	else if (mmc_can_sleep(host->card))
>  		err = mmc_sleep(host);
> @@ -2191,7 +2202,7 @@ static int mmc_shutdown(struct mmc_host *host)
>  	 * before we can shutdown it properly.
>  	 */
>  	if (mmc_can_poweroff_notify(host->card) &&
> -		!(host->caps2 & MMC_CAP2_FULL_PWR_CYCLE))
> +	    !mmc_may_poweroff_notify(host, true))
I guess this deserve some extra documentation because:
If MMC_CAP2_FULL_PWR_CYCLE is not set but MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND is set,
!mmc_may_poweroff_notify(host, true) will evaluate to false while !(host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) will evaluate to true.

Thanks,
Avri

>  		err = _mmc_resume(host);
> 
>  	if (!err)
> --
> 2.43.0
>

On Mon, 31 Mar 2025 at 12:46, Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
>
> Hi Ulf,
>
> > > > > +static bool mmc_may_poweroff_notify(const struct mmc_host *host,
> > > > > +                               bool is_suspend)
> > >
> > > Maybe add some comments about the difference between
> > > mmc_can_poweroff_notify() and mmc_may_poweroff_notify()? Like make it
> > > super-obvious, so I will easily remember next year again :)
> >
> > mmc_can_* functions are mostly about checking what the card is capable
> > of. So mmc_can_poweroff_notify() should be consistent with the other
> > similar functions.
> >
> > For eMMC power-off notifications in particular, it has become more
> > complicated as we need to check the power-off scenario along with the
> > host's capabilities, to understand what we should do.
> >
> > I am certainly open to another name than mmc_may_power_off_notify(),
> > if that is what you are suggesting. Do you have a proposal? :-)
>
> Initially, I didn't think of new names but some explanation in comments.
> But since you are mentioning a rename now, how about:
>
> mmc_card_can_poweroff_notify() and mmc_host_can_poweroff_notify()?

mmc_card_can_poweroff_notify() would not be consistent with all the
other mmc_can_* helpers, so I rather stay with
mmc_can_poweroff_notify(), for now. If you think a rename makes sense,
I suggest we do that as a follow up and rename all the helpers.

mmc_host_can_poweroff_notify() seems fine to me!

>
> Similar to the commit 32f18e596141 ("mmc: improve API to make clear
> hw_reset callback is for cards") where I renamed 'hw_reset' to
> 'card_hw_reset' for AFAICS similar reasons.
>
> > > > >     if (mmc_can_poweroff_notify(host->card) &&
> > > > > -           !(host->caps2 & MMC_CAP2_FULL_PWR_CYCLE))
> > > > > +       !mmc_may_poweroff_notify(host, true))
> > > > I guess this deserve some extra documentation because:
> > > > If MMC_CAP2_FULL_PWR_CYCLE is not set but MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND is set,
> > > > !mmc_may_poweroff_notify(host, true) will evaluate to false while !(host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) will evaluate to true.
> >
> > Right. See more below.
> >
> > >
> > > I agree, I neither get this. Another way to express my confusion is: Why
> > > do we set the 'is_suspend' flag to true in the shutdown function?
> > >
> >
> > I understand your concern and I agree that this is rather messy.
> > Anyway, for shutdown, we set the is_suspend flag to false. The
> > reasoning behind this is that during shutdown we know that the card
> > will be fully powered-down (both vcc and vccq will be cut).
> >
> > In suspend/runtime_suspend, we don't really know as it depends on what
> > the platform/host is capable of. If we can't do a full power-off
> > (maybe just vcc can be cut), then we prefer the sleep command instead.
>
> I do understand that. I don't see why this needs a change in the
> existing logic as Alan pointed out above.

Aha. I get your point now. As stated in the commit message:

Due to an earlier suspend request the eMMC may already have been properly
powered-off, hence we are sometimes leaving the eMMC in its current state.
However, in one case when the host has MMC_CAP2_FULL_PWR_CYCLE_IN_SUSPEND
set we may unnecessarily restore the power to the eMMC, let's avoid this.

To further clarify, at a system suspend we issue a poweroff-notify for
the case above. At system resume we leave the card in powered-off
state until there is I/O (when we runtime resume it). If a shutdown
occurs before I/O, we would unnecessarily re-initialize the card as
it's already in the correct state.

Let me try to clarify the commit message a bit with this information.

>
> > I was hoping that patch3 should make this more clear (using an enum
>
> Sadly, it didn't. Using MMC_POWEROFF_SUSPEND first and then later
> MMC_POWEROFF_SHUTDOWN in mmc_shutdown() is still confusing. Do you want
> to return false in case none of the two PWR_CYCLE flags is set?
>
> > type), but I can try to add some comment(s) in the code to further
> > clarify the policy.
>
> Please do.
>
> All the best,
>
>    Wolfram
>

Thanks!

Kind regards
Uffe