On Wed, Mar 6, 2013 at 3:06 PM, Bjørn Mork [off-list ref] wrote:

Ming Lei [off-list ref] writes:

quoted

On Wed, Mar 6, 2013 at 10:51 AM, Ming Lei [off-list ref] wrote:

quoted

On Wed, Mar 6, 2013 at 12:08 AM, Bjørn Mork [off-list ref] wrote:

quoted

I guess proper error handling here require the USB core to see the
interface driver as dead if it fails to suspend on system suspend, and
do forced rebinding on resume.

The idea should be fine, but may cause regression of user space, suppose
one device with suspend failure can be across suspend-resume cycle and
work well before, but it is no longer with your forced rebinding.

Give the potential cost(user space regression) of doing rebind, I think it
is better to try to recover the device in resume() first, then
consider rebinding
as the last straw.  In fact, I am also wondering if resume() can't recover one
device but probe() can, maybe we can always let resume() recover the
device which experienced suspend failure.

Yes, sure. Drivers wanting to do this, anticipating typical errors, can
still return 0 from suspend and do whatever they want in resume.

My proposal is to make the USB core properly deal with drivers returning
an error from suspend, and also document the fact that a driver should
always return 0 on system suspend unless it really want forced unbinding
on suspend errors.

quoted

I remember that some guys went against rebinding during system sleep before
in the firmware loading discussion.

Yes, that is probably relevant. I'll look it up.  Thanks for the
pointer.

You are welcome!

Here is one link I found:

       http://marc.info/?l=linux-usb&m=132557022902261&w=2

IMO, we unbind interface which hasn't suspend/resume callback
during suspend because there is no better way to handle the case.
But for the suspend failure case, maybe rebind isn't necessary, and
we can document that drivers have to handle their system suspend
failure in resume(), where it is very suitable to do PM recovery.

Also we may store the failure code into usb_interface, and let
USB core check if the suspend failure has been handled/cleared
after resume().

Thanks,
--
Ming Lei
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