On Thu, Sep 11, 2014 at 05:16:44PM +0100, Doug Anderson wrote: > Some 32-bit (ARMv7) systems are architected like this: > > * The firmware doesn't know and doesn't care about hypervisor mode and > we don't want to add the complexity of hypervisor there. > > * The firmware isn't involved in SMP bringup or resume. > > * The ARCH timer come up with an uninitialized offset between the > virtual and physical counters. Each core gets a different random > offset. > > On systems like the above, it doesn't make sense to use the virtual > counter. There's nobody managing the offset and each time a core goes > down and comes back up it will get reinitialized to some other random > value. You probably need to rephrase this slightly, as there *is* still a requirement on the hypervisor/firmware (actually, two!). See below. > Let's add a property to the device tree to say that we shouldn't use > the virtual timer. Firmware could potentially remove this property > before passing the device tree to the kernel if it really wants the > kernel to use a virtual timer. > > Note that it's been said that ARM64 (ARMv8) systems the firmware and > kernel really can't be architected as described above. That means > using the physical timer like this really only makes sense for ARMv7 > systems. I'd go further: this only makes sense if you're booting in secure SVC mode. > In order for this patch to do anything useful, we also need Sonny's > patch at <https://patchwork.kernel.org/patch/4790921/> > > Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx> > Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx> > --- > Changes in v2: > - Add "#ifdef CONFIG_ARM" as per Will Deacon > > Documentation/devicetree/bindings/arm/arch_timer.txt | 6 ++++++ > drivers/clocksource/arm_arch_timer.c | 5 +++++ > 2 files changed, 11 insertions(+) > > diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt > index 37b2caf..876d32b 100644 > --- a/Documentation/devicetree/bindings/arm/arch_timer.txt > +++ b/Documentation/devicetree/bindings/arm/arch_timer.txt > @@ -22,6 +22,12 @@ to deliver its interrupts via SPIs. > - always-on : a boolean property. If present, the timer is powered through an > always-on power domain, therefore it never loses context. > > +** Optional properties: > + > +- arm,use-physical-timer : Don't ever use the virtual timer, just use the > + physical one. Not supported for ARM64. I'd say `Only supported for ARM' to better match what we've done. Probably also worth mentioning that this relies on the hypervisor/firmware having set CNTHCTL.PL1PCEN and CNTHCTL.EL1PCTEN (but assumedly made a mess of CNTVOFF ;) if you want to boot on the non-secure side (e.g. as a guest). Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
