Messages in this thread | | | Date | Wed, 26 Nov 2014 13:49:42 +0100 | From | Daniel Lezcano <> | Subject | Re: [PATCH v4] clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers |
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On 10/08/2014 09:33 AM, Sonny Rao wrote: > From: Doug Anderson <dianders@chromium.org> > > 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 (CNTVOFF) > between the virtual and physical counters. Each core gets a > different random offset. > > * The device boots in "Secure SVC" mode. > > * Nothing has touched the reset value of CNTHCTL.PL1PCEN or > CNTHCTL.PL1PCTEN (both default to 1 at reset) > > 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. > > This adds an optional property which can inform the kernel of this > situation, and firmware is free to remove the property if it is going > to initialize the CNTVOFF registers when each CPU comes out of reset. > > Currently, the best course of action in this case is to use the > physical timer, which is why it is important that CNTHCTL hasn't been > changed from its reset value and it's a reasonable assumption given > that the firmware has never entered HYP mode. > > Note that it's been said that on 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. > > Signed-off-by: Doug Anderson <dianders@chromium.org> > Signed-off-by: Sonny Rao <sonnyrao@chromium.org> > Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
I would be nice to have Catalin's ack.
Thanks
-- Daniel
> --- > Changes in v2: > - Add "#ifdef CONFIG_ARM" as per Will Deacon > > Changes in v3: > - change property name to arm,cntvoff-not-fw-configured and specify > that the value of CNTHCTL.PL1PC(T)EN must still be the reset value > of 1 as per Mark Rutland > > Changes in v4: > - change property name to arm,cpu-registers-not-fw-configured and > specify that all cpu registers must have architected reset values > per Mark Rutland > - change from "#ifdef CONFIG_ARM" to "if (IS_ENABLED(CONFIG_ARM))" per > Arnd Bergmann > --- > Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++ > drivers/clocksource/arm_arch_timer.c | 8 ++++++++ > 2 files changed, 16 insertions(+) > > diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt > index 37b2caf..256b4d8 100644 > --- a/Documentation/devicetree/bindings/arm/arch_timer.txt > +++ b/Documentation/devicetree/bindings/arm/arch_timer.txt > @@ -22,6 +22,14 @@ 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,cpu-registers-not-fw-configured : Firmware does not initialize > + any of the generic timer CPU registers, which contain their > + architecturally-defined reset values. Only supported for 32-bit > + systems which follow the ARMv7 architected reset values. > + > + > Example: > > timer { > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index 8daf056..799139f 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -654,6 +654,14 @@ static void __init arch_timer_init(struct device_node *np) > arch_timer_detect_rate(NULL, np); > > /* > + * If we cannot rely on firmware initializing the timer registers then > + * we should use the physical timers instead. > + */ > + if (IS_ENABLED(CONFIG_ARM) && > + of_property_read_bool(np, "arm,cpu-registers-not-fw-configured")) > + 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 > * that a guest can use the virtual timer instead. >
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