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

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Message-ID: <Z-pyfv_7gJ72YWhz@shikoro>
Date: Mon, 31 Mar 2025 12:46:22 +0200
From: Wolfram Sang <wsa+renesas@...g-engineering.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Avri Altman <Avri.Altman@...disk.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] mmc: core: Further avoid re-storing power to the
 eMMC before a shutdown

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()?

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.

> 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


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