On 07/01/2012 03:45 AM, Tony Lindgren wrote: > * Shilimkar, Santosh <santosh.shilimkar@xxxxxx> [120629 21:23]: >> On Fri, Jun 29, 2012 at 10:52 PM, Jon Hunter <jon-hunter@xxxxxx> 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. So that raises a good point. Looking at the stable branch (3.4.4) it is missing 3 other fixes too [1][2][3]. So this particular problem would not have been exposed, however, I am wondering if there are other problems lingering there. This is a regression is exposed by [2]. I should add that to the changelog. Cheers Jon [1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b3c64bc30af67ed328a8d919e41160942b870451 [2] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1b1287032df3a69d3ef9a486b444f4ffcca50d01 [3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=22770de11cb13e7120f973bca6c800de371a6717 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
