[PATCH 1/2] gpio-vbus: support disabling D+ pullup on suspend

[balbi@ti.com (Felipe Balbi)]

Hi,

On Wed, Jun 22, 2011 at 06:15:17PM +0400, Dmitry Eremin-Solenikov wrote:
> On 6/22/11, Felipe Balbi <balbi@ti.com> wrote:
> > Hi,
> >
> > On Wed, Jun 22, 2011 at 05:52:18PM +0400, Dmitry Eremin-Solenikov wrote:
> >> On 6/22/11, Felipe Balbi <balbi@ti.com> wrote:
> >> > Hi,
> >> >
> >> > On Wed, Jun 22, 2011 at 04:20:16PM +0400, Dmitry Eremin-Solenikov wrote:
> >> >> Some platforms would like to disable D+ pullup on suspend, to drain as
> >> >> low power, as possible. E.g. this was requested by mioa701 board
> >> >> maintainers.
> >> >
> >> > I think this makes sense to many platforms, but by doing so, you would
> >> > loose connection to the Host PC, so you need to make sure your device
> >> > isn't been used before you go down this road.
> >>
> >> I've thought about this. Should UDC driver should somehow call into OTG
> >> layer on suspend? My understanding is that otg_set_suspend isn't the call
> >> that should be done here, is it true?
> >>
> >> My idea was that board can ask for D+ disabling, knowing itself the
> >> behaviour
> >> of the platform driver on suspend (e.g. PXA27x does disable UDC on
> >> suspend,
> >> but I dunno what effect this will cause on Host PC).
> >
> > Host PC will only see the device disconnecting. So, what happens if the
> > user has mounted file systems when you decide to go into suspend ?
> 
> What happens if user has mounted filesystems when I decide to pull out
> the cable?

for starters you could have filesystem corruption. In short, the best
way would be to return -EBUSY in your suspend if the cable is still
attached.

You could use osme VBUS IRQ to toggle a driver flag which, if true,
would return -EBUSY on suspend().

> I agree with you generally, but I'd like to hear any suggestions.

I'm not sure how to solve this, but OTOH the original code already did
this, just on a different way, right ?

-- 
balbi
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 490 bytes
Desc: Digital signature
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20110622/7a844ca7/attachment.sig>