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

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

> 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:
> >
> > Hi again,
> >
> > > 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

So, I think the MMC subsystem should not enter sleep mode
on such environment. If this is board-specific, I'm thinking
I should add a new flag to fix the issue which is entering
sleep mode even if VCCQ=OFF.

> > - ideal   : Either POWER_OFF_LONG or POWER_OFF_SHORT (because the same as the "Shutdown" event)
> > - current : issue MMC_SLEEP_AWAKE --> NG
> > - Remarks : So, I tried to fix this by the patch.
> >
> > In addition, we should also think about the event of unbind.
> 
> Yes, very good point.
> 
> >
> > 4) Event  : Unbind
> > - power   : Keep VCC=ON & VCCQ=ON
> > - ideal   : NO_POWER_NOTIFICATION because user is possible to turn the power off
> > - current : Keep POWERED_ON --> NG
> > - Remarks : But, I didn't try to fix this yet.
> 
> I don't quite understand why we should keep VCC and VCCQ on?

Oops. I should have described a use case. I thought one of use cases was
using mmc_test driver. So, I thought we should keep VCC and VCCQ on to
use mmc_test driver.

> In principle I think we should treat "unbind" in the similar way as we
> treat S2R/S2I. Which means sending power-off-notification if the host
> supports MMC_CAP2_FULL_PWR_CYCLE, otherwise we should send sleep.

If we didn't take care of mmc_test driver after unbind, I think so.

Best regards,
Yoshihiro Shimoda

> Kind regards
> Uffe