Re: [PATCH/RFC] mmc: core: Issue power_off_notify for eMMC Suspend-to-RAM

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Ulf,

On Mon, Jun 8, 2020 at 1:47 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On Mon, 8 Jun 2020 at 12:39, Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@renesas.com> wrote:
> > > From: Ulf Hansson, Sent: Monday, June 8, 2020 5:14 PM
> > > On Thu, 4 Jun 2020 at 14:17, Yoshihiro Shimoda
> > > <yoshihiro.shimoda.uh@renesas.com> wrote:
> > > > > From: Yoshihiro Shimoda, Sent: Tuesday, May 19, 2020 8:33 PM
> > > > >
> > > > > The commit 432356793415 ("mmc: core: Enable power_off_notify for
> > > > > eMMC shutdown sequence") enabled the power off notification
> > > > > even if MMC_CAP2_POWEROFF_NOTIFY (MMC_CAP2_FULL_PWR_CYCLE now) is
> > > > > not set. However, the mmc core lacks to issue the power off
> > > > > notificaiton when Suspend-to-{RAM,Disk} happens on the system.
> > > > >
> > > > > So, add Suspend-to-RAM support at first because this is easy to
> > > > > check by using pm_suspend_target_state condition on _mmc_suspend().
> > > > >
> > > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > > >
> > > > I'd like to add more detail why this patch is needed.
> > > > I think we should think some events (which are Shutdown, Suspend-to-idle,
> > > > Suspend-to-RAM) for the Power off Notification control.
> > > > I described these events like below.
> > > >
> > > > Assumption of the host : MMC_CAP2_FULL_PWR_CYCLE=false
> > > > Assumption of the eMMC : in POWERED_ON
> > > >
> > > > 1) Event  : Shutdown
> > > > - power   : going to VCC=OFF & VCCQ=OFF
> > > > - ideal   : Either POWER_OFF_LONG or POWER_OFF_SHORT
> > > > - current : POWER_OFF_LONG --> Perfect
> > > > - Remarks : the commit 432356793415
> > > >
> > > > 2) Event  : Suspend-to-Idle
> > > > - power   : Keep VCC=ON & VCCQ=ON
> > > > - ideal   : issue MMC_SLEEP_AWAKE and keep the power (because the host could not change VCC=OFF)
> > > > - current : issue MMC_SLEEP_AWAKE and keep the power --> Perfect
> > > > - Remarks : IIUC, even if the eMMC is in POWERED_ON, a host can issue CMD5 (sleep).
> > >
> > > As a matter of fact, VCCQ *must* remain on in sleep state, while VCC
> > > can be powered off.
> >
> > I got it.
> >
> > > >
> > > > 3) Event  : Suspend-to-RAM
> > > > - power   : going to VCC=OFF & VCCQ=OFF
> > >
> > > I don't understand why you think S2R should be treated differently
> > > from S2I? At least from the MMC subsystem point of view, there is no
> > > difference. No?
> >
> > On my environment, VCC & VCCQ condition differs like below.
> >  S2I: VCC=ON & VCCQ=ON
> >  S2R: VCC=OFF & VCCQ=OFF
>
> Can you explain why it differs? Who is managing the regulators and who
> decides to turn them off?

The firmware does, through PSCI system suspend.
And what it does exactly is not standardized.
Perhaps we do need an "arm,psci-system-suspend-is-power-down"[1]
DT property?

> Perhaps this is a regulator-enable usage count problem?

Unfortunately not. Else we could fix it :-)

[1] "[PATCH/RFC 4/6] drivers: firmware: psci: Fix non-PMIC wake-up if
SYSTEM_SUSPEND cuts power"
      https://lore.kernel.org/linux-arm-kernel/1487622809-25127-5-git-send-email-geert+renesas@glider.be/

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds