usb: musb: fix enumeration after resume

[Bin Liu <b-liu@ti.com>]

On Tue, Feb 06, 2018 at 08:00:24PM +0100, Andreas Kemnade wrote:
> Hi,
> 
> On Tue, 6 Feb 2018 12:46:05 -0600
> Bin Liu <b-liu@ti.com> wrote:
> 
> > Hi,
> > 
> > On Sat, Jan 27, 2018 at 09:34:03AM +0100, Andreas Kemnade wrote:
> > > On dm3730 there are enumeration problems after resume.
> > > Investigation led to the cause that the MUSB_POWER_SOFTCONN
> > > bit is not set. If it was set before suspend (because it
> > > was enabled via musb_pullup()), it is set in
> > > musb_restore_context() so the pullup is enabled. But then
> > > musb_start() is called which overwrites MUSB_POWER and
> > > therefore disables MUSB_POWER_SOFTCONN, so no pullup is
> > > enabled and the device is not enumerated.  
> >  
> > Do you see the issue with the v4.15?
> > 
> Yes. Tested without other patches. 
> It was also there in earlier kernels but I had not had motivation enough
> to debug.

Applied to my tree. Thanks.

> So maybe it deserves a CC: Stable

I would prefer it is first tested on each stable tree.

> > > So let's do a subset of what musb_start() does
> > > in the same way as musb_suspend() does it. Platform-specific
> > > stuff it still called as there might be some phy-related stuff
> > > which needs to be enabled.
> > > Also interrupts are enabled, as it was the original idea
> > > of calling musb_start() in musb_resume() according to
> > > Commit 6fc6f4b87cb3 ("usb: musb: Disable interrupts on suspend,
> > > enable them on resume")  
> > 
> > The logic in the fix makes sense, and I do see the same problem with
> > AM335x on v4.9 kernel, but it doesn't happen on v4.15. I haven't checked
> > if there is anything after musb_start() which sets MUSB_POWER_SOFTCON
> > bit.

On v4.15, the SESSION bit is set later which sets the SOFTCON bit. I
didn't check how come v4.9 doesn't invoke it though.

Regards,
-Bin.
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