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

Hi Ulf,

From: Ulf Hansson, Sent: Friday, June 26, 2020 8:03 PM

+ Rob

On Thu, 25 Jun 2020 at 11:26, Geert Uytterhoeven [off-list ref] wrote:

quoted

Hi Shimoda-san,

CC broonie

On Thu, Jun 25, 2020 at 8:31 AM Yoshihiro Shimoda
[off-list ref] wrote:

quoted

quoted

From: Geert Uytterhoeven, Sent: Wednesday, June 24, 2020 8:13 PM
On Wed, Jun 24, 2020 at 12:06 PM Ulf Hansson [off-list ref] wrote:

quoted

On Mon, 22 Jun 2020 at 04:25, Yoshihiro Shimoda
[off-list ref] wrote:

quoted

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.

quoted

quoted

--- 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...

quoted

quoted

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.

quoted

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 (local)

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

But, what do you think?

[2]
https://lore.kernel.org/linux-renesas-soc/1592792699-24638-1-git-send-email-yoshihiro.shimoda.uh@renesas.com/T/#mde38d5866b7f3edc9a2ed105ac06b4fda4c3e99e (local)

[3]
https://lore.kernel.org/linux-renesas-soc/1592792699-24638-1-git-send-email-yoshihiro.shimoda.uh@renesas.com/T/#mf8e7abdf135586ba0b70a1c235410a6f94c6007d (local)

[4]
https://lore.kernel.org/linux-renesas-soc/CAMuHMdX93Q9WhKLqv_wNPzArbc68NcbVN8jJ9MDKxAcicpBQ5Q@mail.gmail.com/T/#m442a2ce972cfdb3ff33637c120c8d096e4d07af8 (local)

Best regards,
Yoshihiro Shimoda

Kind regards
Uffe

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