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: <CAPDyKFr0MvQDxsi-Qd0F=1KuR4Gy6s5bhVdOXRt9K14Z9sO2Kw@mail.gmail.com>
Date: Mon, 31 Mar 2025 11:13:53 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>, Avri Altman <Avri.Altman@...disk.com>, 
	Ulf Hansson <ulf.hansson@...aro.org>, 
	"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

On Mon, 31 Mar 2025 at 10:21, Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
>
>
> > > +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? :-)

>
> > >     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 was hoping that patch3 should make this more clear (using an enum
type), but I can try to add some comment(s) in the code to further
clarify the policy.

Thanks for reviewing and testing!

Kind regards
Uffe