On 08/03/2022 15:24, Vincent Whitchurch wrote:
> The ARTPEC-8 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 FRC 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, we 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 usecase, add a property to the binding to specify the
> first local timer index to be used. If this parameter is non-zero, the
> global timer interrupts will also not be used.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
> ---
>
> Notes:
> v2: New.
>
> .../bindings/timer/samsung,exynos4210-mct.yaml | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/timer/samsung,exynos4210-mct.yaml b/Documentation/devicetree/bindings/timer/samsung,exynos4210-mct.yaml
> index dce42f1f7574..46f466081836 100644
> --- a/Documentation/devicetree/bindings/timer/samsung,exynos4210-mct.yaml
> +++ b/Documentation/devicetree/bindings/timer/samsung,exynos4210-mct.yaml
> @@ -47,6 +47,15 @@ properties:
> reg:
> maxItems: 1
>
> + local-timer-index:
You need vendor prefix. Also this should describe the actual hardware,
not driver behavior, so rather:
"samsung,local-timers"
with a uint32-array type and list of timers to use.
You also need separate property to skip FRC, so something like:
"samsung,frc-shared"
of type boolean.
In the bindings please describe the hardware, not the result you want to
achieve from driver model point of view.
Also disallow this for all other compatibles:
allOf:
- if:
not:
properties:
...
then:
properties:
samsung,local-timers: false
samsung,frc-shared: false
The property simply should not be used outside of Artpec8. It's not
valid in other configurations.
> + $ref: /schemas/types.yaml#/definitions/uint32
> + default: 0
> + maximum: 15 # Last local timer index
> + description: |
> + If present, sets the first local timer index to use. If this value is
> + set to a non-default value, the global timer will not be used for
> + interrupts.
Do not describe the driver, but the hardware. Instead explain which
local timers are allowed to be used.
> +
> interrupts:
> description: |
> Interrupts should be put in specific order. This is, the local timer
Best regards,
Krzysztof
