Re: [PATCH v3 1/4] dt-bindings: timer: exynos4210-mct: Add ARTPEC-8 MCT support

From: Rob Herring
Date: Thu Apr 07 2022 - 11:04:25 EST


On Thu, Apr 07, 2022 at 09:44:29AM +0200, Vincent Whitchurch wrote:
> The ARTPEC-8 has an MCT with 4 global and 8 local timer interrupts.
>
> The SoC has a quad-core Cortex-A53 and a single-core Cortex-A5 which
> share one MCT with one global and eight local timers. The Cortex-A53
> and Cortex-A5 do not have cache-coherency between them, and therefore
> run two separate kernels.
>
> The Cortex-A53 boots first and starts the global free-running counter
> and also registers a clock events device using the global timer. (This
> global timer clock events is usually replaced by arch timer clock events
> for each of the cores.)
>
> When the A5 boots (via the A53), it should not use the global timer
> interrupts or write to the global timer registers. This is because even
> if there are four global comparators, the control bits for all four are
> in the same registers, and we would need to synchronize between the
> cpus. Instead, the global timer FRC (already started by the A53) should
> be used as the clock source, and one of the local timers which are not
> used by the A53 can be used for clock events on the A5.
>
> To support this hardware, add a compatible for the MCT as well as two
> new properties to describe the hardware-mandated sharing of the FRC and
> dedicating local timers to specific processors.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
> ---
>
> Notes:
> v3:
> - Add all required bindings for ARTPEC-8 in one patch
> - Rename and split local-timer-only to samsung,local-timers and
> samsung,frc-shared
> - Restrict above properties to the ARTPEC-8 compatible.
> - Rewrite descriptions of properties to hopefully describe hardware.
>
> v2:
> - Use devicetree property instead of module parameter.
>
> .../timer/samsung,exynos4210-mct.yaml | 26 +++++++++++++++++++
> 1 file changed, 26 insertions(+)

What's this based on? Doesn't apply on v5.18-rc1.

Rob