On Mon, 2016-09-19 at 14:02 -0400, Alan Stern wrote:
> > We can for sure enable autosuspend for the sdmmc device, although as
> > soon as an SD card will be detected the rtsx driver will increase
> the
> > runtime PM usage count. The count is decreased when the card is
> > removed (or failed to be initialized), thus runtime suspend is
> > prevented as long as there is a functional card inserted.

Testing autosuspend with card readers on usb_storage I saw a uniform
response of reporting a medium change event upon resume.
I am afraid other kinds of readers are not better in that regard.
> 
> Which means that autosuspend matters only when a card isn't present, 
> and the host is polled every second or so to see whether a card has 
> been inserted.
> 
> Under those circumstances you probably don't want to use
> autosuspend.  
> That is, resuming before each poll and suspending afterward may use 
> less energy than staying at full power all the time.

Is that based on concrete figures about power consumption?

And it seems to me that we need a way to indicate that the heuristics
should not be used, but a device immediately suspended. The timer
is sensible only if the next wakeup is unknown.

        Regards
                Oliver



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