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

[frankyl@broadcom.com (Franky Lin)]

On 06/29/2012 10:22 AM, Jon Hunter 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.
> 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
>     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@secretlab.ca>
> Cc: Linus Walleij <linus.walleij@stericsson.com>
> Cc: Kevin Hilman <khilman@ti.com>
> Cc: Tarun Kanti DebBarma <tarun.kanti@ti.com>
> Cc: Franky Lin <frankyl@broadcom.com>
>
> Reported-by: Franky Lin <frankyl@broadcom.com>
> Signed-off-by: Jon Hunter <jon-hunter@ti.com>
> ---

Tested-by: Franky Lin <frankyl@broadcom.com>