[PATCH v3 2/2] mmc: core: Call mmc_poweroff_nofity() if pm_suspend_via_firmware()

Mon Jul 6 09:10:44 EDT 2020

On Thu, 2 Jul 2020 at 14:37, Yoshihiro Shimoda
<yoshihiro.shimoda.uh at renesas.com> wrote:
>
> Hi Ulf,
>
> > From: Ulf Hansson, Sent: Friday, June 26, 2020 8:03 PM
> >
> > + Rob
> >
> > On Thu, 25 Jun 2020 at 11:26, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> > >
> > > Hi Shimoda-san,
> > >
> > > CC broonie
> > >
> > > On Thu, Jun 25, 2020 at 8:31 AM Yoshihiro Shimoda
> > > <yoshihiro.shimoda.uh at renesas.com> wrote:
> > > > > From: Geert Uytterhoeven, Sent: Wednesday, June 24, 2020 8:13 PM
> > > > > On Wed, Jun 24, 2020 at 12:06 PM Ulf Hansson <ulf.hansson at linaro.org> wrote:
> > > > > > On Mon, 22 Jun 2020 at 04:25, Yoshihiro Shimoda
> > > > > > <yoshihiro.shimoda.uh at renesas.com> wrote:
> > > > > > > If pm_suspend_via_firmware() returns true, the system will be able
> > > > > > > to cut both vcc and vccq in the suspend. So, call
> > > > > > > mmc_poweroff_nofity() if pm_suspend_via_firmware() returns true.
> > > > > > >
> > > > > > > Note that we should not update the MMC_CAP2_FULL_PWR_CYCLE caps
> > > > > > > because the mmc_select_voltage() checks the caps when attaches
> > > > > > > a mmc/sd.
> > > > >
> > > > > > > --- a/drivers/mmc/core/mmc.c
> > > > > > > +++ b/drivers/mmc/core/mmc.c
> > > > > > > @@ -2038,7 +2039,8 @@ 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) || !is_suspend ||
> > > > > > > +            pm_suspend_via_firmware()))
> > > > > >
> > > > > > Sorry, but this doesn't work.
> > > > > >
> > > > > > Even if PSCI is a generic FW interface, it doesn't mean that all PSCI
> > > > > > implementations will cut the vcc and vccq for the MMC card at system
> > > > > > suspend.
> > > > >
> > > > > Indeed, there's nothing guaranteed here.  Nor documented how it should
> > > > > behave.  Basically the firmware is free to power off the SoC. Or not do that.
> > > > > "If firmware is involved, all odds are off".
> > > >
> > > > I thought we could be guaranteed. But, I understood we could not be guaranteed...
> > > >
> > > > > > Instead, you need to decide this based on some specific DT property.
> > > > > > Perhaps in conjunction with using pm_suspend_via_firmware().
> > > > >
> > > > > Last time I was involved in a discussion about this, the PSCI people
> > > > > didn't want to add any properties describing particular PSCI behavior...
> > > > > "If firmware is involved, all odds are off".
> > > > >
> > > > > So the only safe thing to do is to expect the worst, and prepare for it...
> > > >
> > > > A headache point is an eMMC device consumes much power if that the system
> > > > doesn't cut the vcc and vccq and doesn’t enter the sleep mode.
> > > > In other words, in power consumption point of view, this patch will
> > > > cause a regression in such a case...
> > >
> > > Indeed.
> > >
> > > > By the way, about adding specific DT property, the regulator can have
> > > > regulator-off-in-suspend property in regulator-state-mem subnode.
> > > > For now, we doesn't seem to get the property from a regulator consumer though.
> > > > So, I'll try to add an API of regulator for it.
> > >
> > > Oh right, the eMMC is described in DT as being connected to two
> > > regulators.
> > > Note that the semantics of regulator-off-in-suspend are that the
> > > regulator should be disabled (by the regulator core) during suspend, not
> > > that the regulator is disabled during suspend by a third party.
> > > No idea if that will work with a fixed-regulator without GPIO control,
> > > but of course you can try.
>
> As other email thread of this trial as v4, I could not get approval [1].
>
> [1]
> https://lore.kernel.org/linux-renesas-soc/CAMuHMdX93Q9WhKLqv_wNPzArbc68NcbVN8jJ9MDKxAcicpBQ5Q@mail.gmail.com/T/#m70883cc5de4fa7fca50118dad743c836d5e3b451
>
> > For mmc we already have a DT property, "full-pwr-cycle". Which tells
> > whether the host is able to completely power-cycle the card (some
> > host's manage power internally).
> >
> > However, maybe the proper thing here would be to add a property of
> > regulator instead.
>
> My v4 patch was using a regulator property. But since I could not get
> approval, we could not use this way, I think.
>
> > If that doesn't make sense, I am also open to add a
> > new MMC property, "full-pwr-cycle-in-suspend".
>
> I thought this way was better. However, I'm wondering if adding such a new MMC
> property to issue Power Off Notification in mmc_suspend() is really better
> than the current implementation. This is because we don't have any completely
> solutions now:
>  - Depend on board configuration (The board doesn't have "full-pwr-cycle").
>  - Depend on firmware on board [2]. So, even if adding a new MMC property,
>    it cannot sync the firmware condition. In fact, this is possible to
>    cause regression in power consumption point of view [3].

This is a generic problem with FWs.

I guess one could try to update the DTB using DT overlays, in case
some FW version changes.

>  - My environment (PSCI which is one of firmware) doesn't support
>    any ability to sync between the firmware and OS for now [4].

Yes, I see.

It seems like Geert has tried different approaches to convince PSCI
folkz, to find a solution for this, but it seems like none have make
it yet.

>
> But, what do you think?

>From the mmc DT property point of view, I am fine adding a
"full-pwr-cycle-in-suspend" - and then also update the mmc core's
behavior to use the eMMC power-off-notify command at system suspend.

However, I don't have a strong opinion, as the current solution with
the eMMC sleep command also seems to work.

My main concern with the current approach though, is not about wasting
energy, but rather that we are not doing a graceful shutdown of the
eMMC device. Instead we just cut VCCQ while the eMMC is "sleeping",
which in worst case could lead to internal data corruptions, but also
increased re-initialization time at system suspend.

>
> [2]
> https://lore.kernel.org/linux-renesas-soc/1592792699-24638-1-git-send-email-yoshihiro.shimoda.uh@renesas.com/T/#mde38d5866b7f3edc9a2ed105ac06b4fda4c3e99e
>
> [3]
> https://lore.kernel.org/linux-renesas-soc/1592792699-24638-1-git-send-email-yoshihiro.shimoda.uh@renesas.com/T/#mf8e7abdf135586ba0b70a1c235410a6f94c6007d
>
> [4]
> https://lore.kernel.org/linux-renesas-soc/CAMuHMdX93Q9WhKLqv_wNPzArbc68NcbVN8jJ9MDKxAcicpBQ5Q@mail.gmail.com/T/#m442a2ce972cfdb3ff33637c120c8d096e4d07af8
>

Kind regards
Uffe