On Mon, 2 Jul 2012 13:26:38 -0500 Jon Hunter <jon-hunter@xxxxxx> wrote: > > On 07/02/2012 01:07 PM, Kevin Hilman wrote: > > + Neil Brown > > > > Hi Jon, > > > > Jon Hunter <jon-hunter@xxxxxx> 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@xxxxxxxxxxxx> > >> Cc: Linus Walleij <linus.walleij@xxxxxxxxxxxxxx> > >> Cc: Kevin Hilman <khilman@xxxxxx> > >> Cc: Tarun Kanti DebBarma <tarun.kanti@xxxxxx> > >> Cc: Franky Lin <frankyl@xxxxxxxxxxxx> > >> > >> Reported-by: Franky Lin <frankyl@xxxxxxxxxxxx> > >> Signed-off-by: Jon Hunter <jon-hunter@xxxxxx> > > > > 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@xxxxxxx> Thanks, NeilBrown
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