Re: [PATCH 2/5] usb: musb: call musb_port_suspend from musb_bus_suspend

[Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>]

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Hi,

On Mon, Nov 25, 2013 at 03:41:14PM -0500, Alan Stern wrote:
> On Mon, 25 Nov 2013, Daniel Mack wrote:
> 
> > >>> What if you have a mounted file system on a pendrive ? Should we allow
> > >>> suspend in that case ?
> > >>
> > >> Well, I would have expected that, but in fact, the opposite is true.
> > >> With 3.12, mounting a filesystem on a USB media and accessing it after
> > >> resume was exactly my test case, and it worked just fine with that patch.
> > > 
> > > so you had a mounted file system, suspend, resume, it was still mounted?
> > 
> > Yes, exactly.
> > 
> > > or did it reenumerate and you remounted it ?
> > 
> > No, it did not reenumerate, but the core did a reset on it. See the
> > following log.
> 
> ...
> > [   32.030792] usb 1-1: reset high-speed USB device number 2 using
> > musb-hdrc <<<< !
> 
> Like I said, you get a reset-resume.
> 
> > > Try to do the same with transfers in flight, it's likely to corrupt your
> > > file system.
> 
> It's not so easy to suspend a system with USB mass-storage transfers in 
> flight.  For one thing, userspace gets frozen before the suspend 
> starts, so there's nothing to initiate new I/O requests (except perhaps 
> for dirty-block writebacks).
> 
> Also, the child SCSI device gets suspended before the USB device, so
> its I/O queue stops running.  In addition, the usb-storage suspend
> routine and the main I/O thread are mutually exclusive (they both grab
> the private mutex), so a suspend can't occur while a SCSI command is
> underway.

awesome, thanks for the explanation Alan :-)

-- 
balbi

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