From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Fri, 26 Jul 2013 16:34:40 +0100 Subject: [PATCH 01/13] ARM: suspend: use hash of cpu_logical_map value to index into save array In-Reply-To: References: <20130726113110.GB28084@e102568-lin.cambridge.arm.com> Message-ID: <20130726153440.GD2282@localhost.localdomain> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jul 26, 2013 at 10:41:38AM -0400, Nicolas Pitre wrote: > On Fri, 26 Jul 2013, Lorenzo Pieralisi wrote: > > > On Thu, Jul 25, 2013 at 05:06:51PM +0100, Nicolas Pitre wrote: > > > On Thu, 25 Jul 2013, Dave Martin wrote: > > > > > > > On Wed, Jul 24, 2013 at 02:55:00PM -0400, Nicolas Pitre wrote: > > > > > On Wed, 24 Jul 2013, Dave Martin wrote: > > > > > > > > > > > But this patch commits us to requiring that on the suspend path > > > > > > specifically -- I think that ought to be mentioned somewhere. A > > > > > > comment in the preamble for __cpu_suspend would be enough, I think. > > > > > > > > > > What comment would you suggest? I want to make sure the possible > > > > > confusion you see is properly addressed. > > > > > > > > I think we just need to state that the value of > > > > cpu_logical_map(smp_processor_id()) must be the MPIDR of the physical > > > > CPU the suspending logical CPU will resume on. Consequently, if doing a > > > > migration, cpu_logical_map() must be updated appropriately somewhere > > > > between cpu_pm_enter() and cpu_suspend(). > > > > > > Excellent. I've amended the patch with this: > > > > > > diff --git a/arch/arm/kernel/suspend.c b/arch/arm/kernel/suspend.c > > > index 2835d35234..caf938db62 100644 > > > --- a/arch/arm/kernel/suspend.c > > > +++ b/arch/arm/kernel/suspend.c > > > @@ -17,6 +17,11 @@ extern void cpu_resume_mmu(void); > > > /* > > > * Hide the first two arguments to __cpu_suspend - these are an implementation > > > * detail which platform code shouldn't have to know about. > > > + * > > > + * On SMP systems, the value of cpu_logical_map(smp_processor_id()) must be > > > + * the MPIDR of the physical CPU the suspending logical CPU will resume on. > > > + * Consequently, if doing a physical CPU migration, cpu_logical_map() must be > > > + * updated appropriately somewhere between cpu_pm_enter() and cpu_suspend(). > > > */ > > > int cpu_suspend(unsigned long arg, int (*fn)(unsigned long)) > > > { > > > > > > I've put it against cpu_suspend() rather than __cpu_suspend(() as this > > > is what users should care about. > > > > > > ACK? > > > > We need this patch to allow IKS to store a cpu context at a specific > > index, let's be honest. It is a moot point and I am not very happy > > about changing this code for a very specific usage, but the way code is > > implemented makes the change acceptable. I really do not think we should > > write guidelines on how cpu_suspend users have to change cpu_logical_map > > though, that's not needed apart from IKS and that should be limited to IKS > > code only. > > > > Again, that's just my opinion, but cpu_suspend API must be kept as it is > > and we should not encourage people to use it in creative ways. > > I tend to agree, but I'm now stuck between two conflicting requests. Would it make sense to keep the same API to cpu_suspend(), but make it a wrapper for another function which has the MPIDR argument? Then people calling cpu_suspend() continue as normal. Only IKS needs to know about the underlying MPIDR handling when calling this. Cheers ---Dave > > Are you saying you are willing to give me your ACK if I revert the > suggested change? > > > Nicolas