Hi Doug, On Tue, Jul 28, 2015 at 6:24 PM, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > Alexey, > > On Mon, Jul 27, 2015 at 2:28 PM, Alexey Klimov <klimov.linux@xxxxxxxxx> wrote: >> Hi all, >> >> year(s) ago it was discovered that MCT timer and ARM architectured >> timer >> are the same hardware with different interface. Here [1]. >> >> I followed mail-list discussions about removing MCT and using arch >> timer for Exynos5-based SoCs but things aren't moving at least latest >> upstream kernel on odroid-xu3 will use MCT as default timers. >> Maybe the reason are some power-management related things that very >> specific to Samsung. I don't know. >> >> >> Idea of this draft patchset comes from Doug patches when he tried to >> optimize read of 64-bit counter located in mmio. [2] >> Why not using cp15 counter instead if possible? > > I hate to burst your bubble here, but... > > ...I think it would be a bad idea to use the cp15 counter on exynos > 5422. According to Samsung, there are issues where using cp15 could > sometimes return the wrong value, especially if you happen to read it > while on an A7 instead of an A15. It will tend to work pretty well, > but Samsung claimed that it might not work right on some CPUs or at > some temperatures. I think this is right time when I can say "If only I had known about it before!". That's quite interesting especially about temperature issues. Maybe it's worth to insert comments in driver/docs about this. > I've added Alim who provided this information to me (in the private > http://crosbug.com/p/29556). He may be able to elaborate more. Alim, could you please add details if any? > Generally I'd say that if the arch timer works for you: use the arch > timer. If the arch timer doesn't work for you, use the MCT. > > -Doug I possess no knowledge if there're any different hw revisions of odroid-xu3 on the field but looks like arch timer works fine for me on odroid-xu3 Exynos5422 SoC with upstream kernel. Is it right direction to switch xu3 to arch timer? Do you have any info or ideas about enabling MCT G_TCON register to start arch timer and what's the best way to do it? Thanks. -- Best regards, Klimov Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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