From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter De Schrijver Subject: Re: [PATCH] ARM: tegra: Use PMC scratch register 40 for tegra_resume() location store Date: Thu, 8 Jan 2015 14:37:09 +0200 Message-ID: <20150108123709.GX10073@tbergstrom-lnx.Nvidia.com> References: <1419202392-1159-1-git-send-email-digetx@gmail.com> <54984429.8040905@wwwdotorg.org> <5498549B.8070101@gmail.com> <54985C30.7020605@wwwdotorg.org> <20150108105742.GI1987@ulmo.nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20150108105742.GI1987@ulmo.nvidia.com> Sender: linux-kernel-owner@vger.kernel.org To: Thierry Reding Cc: Stephen Warren , linux-arm-kernel@lists.infradead.org, Alexandre Courbot , Russell King , Stefano Stabellini , Sekhar Nori , linux-kernel@vger.kernel.org, Haojian Zhuang , stable@vger.kernel.org, Joseph Lo , linux-tegra@vger.kernel.org, Dmitry Osipenko , Shawn Guo , Christoffer Dall List-Id: linux-tegra@vger.kernel.org On Thu, Jan 08, 2015 at 11:57:43AM +0100, Thierry Reding wrote: > * PGP Signed by an unknown key >=20 > On Mon, Dec 22, 2014 at 11:00:16AM -0700, Stephen Warren wrote: > > On 12/22/2014 10:27 AM, Dmitry Osipenko wrote: > > >22.12.2014 19:17, Stephen Warren =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > >>On 12/21/2014 03:52 PM, Dmitry Osipenko wrote: > > >>>Commit 7232398abc6a ("ARM: tegra: Convert PMC to a driver") chan= ged > > >>>tegra_resume() > > >>>location storing from late to early and as result broke suspend = on tegra20. > > >>>PMC scratch register 41 was used by tegra lp1 suspend core code = for storing > > >>>physical memory address of common resume function and in the sam= e time used by > > >>>tegra20 cpuidle driver for storing cpu1 "resettable" status, so = it implied > > >>>strict order of scratch register use. Fix it by using scratch 40= instead of 41 > > >>>for tegra_resume() location store. > > >> > > >>You likely can't simply change the PMC scratch register usage arb= itrarily; > > >>specific registers are designated for specific purposes, and code= outside the > > >>Linux kernel (bootloaders, LP0 resume code, secure monitors, etc.= ) may depend on > > >>those specific values being in those registers. Without significa= nt research, > > >>I'd suggest not changing the PMC scratch register usage. > > > > > >Sure, that's why I asked to verify if scratch register 40 is in us= e in the > > >comment after commit message. > >=20 > > Sorry, I didn't notice that. > >=20 > > >I've checked that u-boot doesn't use it (since > > >upstream kernel doesn't care about any other bootloader), but no i= dea about > > >secure monitor. It's definitely safer to avoid changing scratch re= gs usage, I > > >thought that proposed solution would be best from the pure code po= int of view. > > >So, I'm considering your answer as a rejection of the patch (pleas= e, let me know > > >if I'm wrong) and will prepare another one. Btw, it would be nice = to have > > >scratch registers usage publicly documented somewhere (on "Tegra P= ublic > > >Application Notes" webpage for example), if it's possible, of cour= se. > >=20 > > At this stage in Tegra20 development, I think it'd be best to avoid= changing > > any scratch register usage if at all possible. >=20 > Sorry, I had completely missed this discussion. When looking at the c= ode > it doesn't look like this particular "resettable" status needs to be > stored in a PMC scratch register. It can't be stored in RAM because t= hat > goes into self-refresh as part of LP1, but how about just putting it > into IRAM? That stays on in both LP1 and LP2, so should be suitable f= or > this use-case. It would make the code slightly more complex but using= a > single scratch register for multiple purposes sounds brittle and easy= to > break (as evidenced by the offending commit). >=20 > Otherwise it would seem that PMC_SCRATCH40 is only used to store EMC > configuration data across LP0 suspend/resume, so I wouldn't think it'= d > cause problems if we used that instead of PMC_SCRATCH41 to store the > "resettable" state. >=20 No. Usually the scratch registers for EMC config data are setup once by= the bootloader and never touched by the kernel after that. So I would not recommend reusing those registers for different purposes. Cheers, Peter.