From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Franky Lin" Subject: Re: [PATCH] gpio/omap: fix invalid context restore of gpio bank-0 Date: Fri, 29 Jun 2012 13:27:42 -0700 Message-ID: <4FEE0FBE.2010307@broadcom.com> References: <1340990551-19426-1-git-send-email-jon-hunter@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mms2.broadcom.com ([216.31.210.18]:1046 "EHLO mms2.broadcom.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932796Ab2F2U1y (ORCPT ); Fri, 29 Jun 2012 16:27:54 -0400 In-Reply-To: <1340990551-19426-1-git-send-email-jon-hunter@ti.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Jon Hunter , linux-omap , linux-arm Cc: Grant Likely , Linus Walleij , Kevin Hilman , Tarun Kanti DebBarma 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 > Cc: Linus Walleij > Cc: Kevin Hilman > Cc: Tarun Kanti DebBarma > Cc: Franky Lin > > Reported-by: Franky Lin > Signed-off-by: Jon Hunter > --- Tested-by: Franky Lin