Messages in this thread | | | Date | Mon, 22 Dec 2014 11:00:16 -0700 | From | Stephen Warren <> | Subject | Re: [PATCH] ARM: tegra: Use PMC scratch register 40 for tegra_resume() location store |
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On 12/22/2014 10:27 AM, Dmitry Osipenko wrote: > 22.12.2014 19:17, Stephen Warren пишет: >> On 12/21/2014 03:52 PM, Dmitry Osipenko wrote: >>> Commit 7232398abc6a ("ARM: tegra: Convert PMC to a driver") changed >>> 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 same 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 arbitrarily; >> 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 significant 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 use in the > comment after commit message.
Sorry, I didn't notice that.
> I've checked that u-boot doesn't use it (since > upstream kernel doesn't care about any other bootloader), but no idea about > secure monitor. It's definitely safer to avoid changing scratch regs usage, I > thought that proposed solution would be best from the pure code point of view. > So, I'm considering your answer as a rejection of the patch (please, 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 Public > Application Notes" webpage for example), if it's possible, of course.
At this stage in Tegra20 development, I think it'd be best to avoid changing any scratch register usage if at all possible.
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