Re: autosleep suspend too frquent problem

[Ulf Hansson]

On 3 June 2014 14:01, Pavel Machek <pavel@xxxxxx> wrote:
> Hi!
>
>
>> I found sd card sometimes are damaged/ destroyed
>> On our devices .
>> And seems it is caused by kernel's frequently suspend/resume,
>> Because during suspend/resume, the driver will suspend/resume sdcard
>> Very frequently, this will damaged the sdcard sometimes, and the damage
>> is not recoverable ..
>>
>> Sometimes kernel will enter suspend and exit suspend very frequently,
>> Especially when the system is in idle, but some driver is not idle,
>> And it will  wake up the system by irq frequently.
>> By our power test result, if system enter suspend /resume very frequently,
>> Will consume more power , because it will enable /disable many devices
>> During a short time .
>>
>> I make a patch to prevent the system to enter suspend/resume state
>> More than one time during 2 secondsï
>
> It is good you managed to diagnose the problem, but this si not the
> right solution.
>
> Either:
>
> 1) don't power down SD card during system suspend

NAK. The amount of power a card (even if there are good behaving cards
as well) may utilize, in powered but idle state could be significant.
I have seen cases of constant power consumption of several mA here.

>
> or maybe even better
>
> 2) don't power _up_ SD card during system resume. Let it be powered
> down until the first access.

Good news! This is "almost" supported already by the mmc subsystem.

If your mmc host has set the capability flag MMC_CAP_RUNTIME_RESUME,
that means the card won't be powered up (and initialized) until the
next request.

However, for removable cards (!MMC_CAP_NONREMOVABLE), during system
resume phase, the mmc core will trigger a "rescan" of the card, to
verify it has not been removed. Thus, unfortunate for this use case,
the first request (for removable cards) will be triggered during the
system resume phase.

I suppose we should add some extra conditions/flags which makes the
mmc core to handle the above scenario. Actually I have been thinking
of putting together a patch for this, but it never pops up on the top
of my TODO list. :-)

Additionally, I wonder if this bouncing up and down from suspend to
resume, could have other negative impact for other subsystems? Is it
just a mmc subsystem problem? I am not so sure.

Kind regards
Ulf Hansson

>
> Thanks,
>                                                                         Pavel
> --
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