On Wed, Aug 27, 2014 at 5:56 PM, Stephen Boyd <sb...@codeaurora.org> wrote: > On 08/27/14 15:33, Olof Johansson wrote: >> On Wed, Aug 27, 2014 at 3:26 PM, Stephen Boyd <sb...@codeaurora.org> wrote: >> >>> Is there any reason why the virtual counter can't be read? Maybe we're >>> the hyp and we need to make sure we don't use the virtual timer so that >>> the guest can use it, but that doesn't have any effect on the usage of >>> the virtual counter for the clocksource. >> There are several cases where virtual is unusable -- in particular it >> might not have been configured properly (i.e. the phys/virt offset is >> at a bad value). >> > > Any specifics? It would be nice to say so in the commit text so that > others using such devices know they need this patch. I'm guessing the > firmware can't be fixed?
Yeah, there are a few. The big.LITTLE on the Chromebook 2 models have this issue, due to the A7 cluster having an incorrect offset programmed. However, arch timers aren't supported on that SoC in the first place, so it's not a problem in reality. The other known platform is rk3288. It has products out in the wild where firmware updates are unlikely. Essentially, I expect many vendors who use BSP kernels by default to have firmware that forgets to setup the offset, since hardware doesn't come up with a default one, and their older BSP kernels doesn't access the virtual one. > In this particular case is there actually a virtual interrupt but we've > explicitly removed it from the DT so that the driver can be forced into > using the physical counter? Or are we getting saved by the hyp check? The SoC has the virtual timer, and if it has firmware that supports it there's a good reason to still have it there. After all, DT describes hardware. I have a patch I should post that adds a property to make the driver pick the physical timer instead, since right now it'll always use virtual if it's available. I'll try to get that posted later tonight. -Olof -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/