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

[NeilBrown]

On Mon, 2 Jul 2012 13:26:38 -0500 Jon Hunter <jon-hunter at ti.com> wrote:

> 
> On 07/02/2012 01:07 PM, Kevin Hilman wrote:
> > + Neil Brown
> > 
> > Hi Jon,
> > 
> > Jon Hunter <jon-hunter at ti.com> writes:
> > 
> >> 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.
> >> 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.
> >> 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
> > 
> > The 'To avoid this...' sentence here doesn't read well.  Looks like you
> > need to:
> > 
> > s/otherwise//
> 
> Yes, I meant to have dropped "otherwise" here. Thanks!
> 
> > s/populated/populate/
> 
> Yes that too! I must have re-worded and screwed it up royally :-(
> 
> > ?
> > 
> >>    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.
> >> [1] http://marc.info/?l=linux-omap&m=134065775323775&w=2
> >>
> >> Cc: Grant Likely <grant.likely at secretlab.ca>
> >> Cc: Linus Walleij <linus.walleij at stericsson.com>
> >> Cc: Kevin Hilman <khilman at ti.com>
> >> Cc: Tarun Kanti DebBarma <tarun.kanti at ti.com>
> >> Cc: Franky Lin <frankyl at broadcom.com>
> >>
> >> Reported-by: Franky Lin <frankyl at broadcom.com>
> >> Signed-off-by: Jon Hunter <jon-hunter at ti.com>
> > 
> > Thanks for digging inot this bug Jon.  The same bug was brought up by
> > Neil Brown (Cc'd) in a different thread.
> > 
> > Neil, it looks to me that this fix will address the problems you were
> > seeing as well.  Care to test, and respond with your ack/tested-by if it
> > works for you?  Thanks.
> 
> Neil let me know your thoughts and if you are ok, I can clean-up the
> changelog and re-send.

Yes, works for me and looks sensible.

 Tested-by: NeilBrown <neilb at suse.de>

Thanks,
NeilBrown
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