On 12/13/2017 12:53 PM, Alexandre Belloni wrote:
> The clocksource and clockevent timer are probed early in the boot process.
> At that time it is difficult for linux to know whether a particular timer
> can be used as the clocksource or the clockevent or by another driver,
> especially when they are all identical or have similar features.
>
> Until now, multiple strategies have been used to solve that:
> - use Kconfig option as MXC_USE_EPIT or ATMEL_TCB_CLKSRC_BLOCK
> - use a kernel parameter as the "clocksource" early_param in mach-omap2
> - registering the first seen timer as a clockevent and the second one as
> a clocksource as in rk_timer_init or dw_apb_timer_init
>
> Add a linux,clocksource and a linux,clockevent node in chosen with a timer
> property pointing to the timer to use. Other properties, like the targeted
> precision may be added later.
>
> Signed-off-by: Alexandre Belloni <alexandre.bell...@free-electrons.com>
> ---
> Documentation/devicetree/bindings/chosen.txt | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/chosen.txt
> b/Documentation/devicetree/bindings/chosen.txt
> index e3b13ea7d2ae..c7ee3ecb5276 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -120,3 +120,23 @@ e.g.
> While this property does not represent a real hardware, the address
> and the size are expressed in #address-cells and #size-cells,
> respectively, of the root node.
> +
> +linux,clocksource and linux,clockevent
> +--------------------------------------
> +
> +Those nodes have a timer property. This property is a phandle to the timer
> to be
> +chosen as the clocksource or clockevent. This is only useful when the
> platform
> +has multiple identical timers and it is not possible to let linux make the
> +correct choice.
> +
> +/ {
> + chosen {
> + linux,clocksource {
> + timer = <&timer0>;
> + };
> +
> + linux,clockevent {
> + timer = <&timer1>;
> + };
> + };
> +};
>
It'd be nice if smth. like this will actually happen, as on some OMAP
platforms can be up to 3-4 alternatives for each clocksource/clockevent and
different combination need to be selected depending on SoC and platform
(and sometime - use case) which is pain in multi-platform environment now.
But more important note from my side is clocksource and clockevent selections
seems
not enough :( There are also sched clock (sched_clock_register()) and
delay_timer
(register_current_timer_delay() at least on ARM).
Both above can't be unregistered (at least last time I've checked).
--
regards,
-grygorii
