On Thu, 4 Jun 2020 at 14:17, Yoshihiro Shimoda
<yoshihiro.shimoda.uh@xxxxxxxxxxx> 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@xxxxxxxxxxx>
>
> 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.
>
> 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?
> - 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?
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.
Kind regards
Uffe
