Hi Doug, On 09/11/2014 11:52 AM, 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. > > 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. > > 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> > --- > Documentation/devicetree/bindings/arm/arch_timer.txt | 6 ++++++ > drivers/clocksource/arm_arch_timer.c | 3 +++ > 2 files changed, 9 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. > + > + > Example: > > timer { > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index 5163ec1..8ca07a9 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -649,6 +649,9 @@ static void __init arch_timer_init(struct device_node *np) > arch_timer_ppi[i] = irq_of_parse_and_map(np, i); > arch_timer_detect_rate(NULL, np); > > + if (of_property_read_bool(np, "arm,use-physical-timer")) > + arch_timer_use_virtual = false; > + > /* > * If HYP mode is available, we know that the physical timer > * has been configured to be accessible from PL1. Use it, so > How's the VDSO supposed to deal with this? It currently does: cycle_now = arch_counter_get_cntvct() Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation. -- 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
