On Wed, Oct 08, 2014 at 12:33:47AM -0700, Sonny Rao wrote: > From: Doug Anderson <dianders@xxxxxxxxxxxx> > > 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@xxxxxxxxxxxx> > Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx> > Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx> > --- > 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 Applied to next/drivers (and next/dt for rk3288 dependency). Thanks, all! -Olof -- 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
