[PATCH] gpio/omap: fix invalid context restore of gpio bank-0

[Tony Lindgren]

* Shilimkar, Santosh <santosh.shilimkar at ti.com> [120629 21:23]:
> On Fri, Jun 29, 2012 at 10:52 PM, Jon Hunter <jon-hunter at ti.com> wrote:
> > Currently the gpio _runtime_resume/suspend functions are calling the
> > get_context_loss_count() platform function if the function is populated for
> > a gpio bank. This function is used to determine if the gpio bank logic state
> > needs to be restored due to a power transition. This function will be populated
> > for all banks, but it should only be called for banks that have the
> > "loses_context" variable set. It is pointless to call this if loses_context is
> > false as we know the context will never be lost and will not need restoring.
> >
> > For all OMAP2+ devices gpio bank-0 is in an always-on power domain and so will
> > never lose context. We found that the get_context_loss_count() was being called
> > for bank-0 during the probe and returning 1 instead of 0 indicating that the
> > context had been lost. This was causing the context restore function to be
> > called at probe time for this bank and because the context had never been saved,
> > was restoring an invalid state. This ultimately resulted in a crash [1].
> >
> > There are multiple bugs here that need to be addressed ...
> >
> > 1. Why the always-on power domain returns a context loss count of 1? This needs
> >   to be fixed in the power domain code. However, the gpio driver should not
> >   assume the loss count is 0 to begin with.
> Indeed. GPIO driver should not assume the value.
> 
> > 2. The omap gpio driver should never be calling get_context_loss_count for a
> >   gpio bank in a always-on domain. This is pointless and adds unneccessary
> >   overhead.
> Make sense too.
> 
> > 3. The OMAP gpio driver assumes that the initial power domain context loss count
> >   will be 0 at the time the gpio driver is probed. However, it could be
> >   possible that this is not the case and an invalid context restore could be
> >   performed during the probe. To avoid this otherwise only populated the
> >   get_context_loss_count() function pointer after the initial call to
> >   pm_runtime_get() has occurred. This will ensure that the first
> >   pm_runtime_put() initialised the loss count correctly.
> >
> > This patch addresses issues 2 and 3 above.

Should this one be Cc: stable? If this is a regression, then the regression
causing commit should be mentioned.

Tony