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

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

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).

3) Event  : Suspend-to-RAM
- power   : going to VCC=OFF & 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.

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.

Best regards,
Yoshihiro Shimoda