[PATCH] clocksource/drivers/arm_arch_timer: export arch_timer_get_rate

[Chanho Park]

Hi,

> On Tue, Jan 12, 2021 at 10:31:40AM +0900, Chanho Park wrote:
> > This patch adds to export arch_timer_get_rate function for calculating
> > absolute timestamp which is based on arch timer like below.
> > arch_timer_read_counter was already exported but arch_timer_get_rate
> > wasn't. Thus, this patch tries to export this to use this function from
> > loadable kernel module.
>
> Can you please explain /where/ this would be used? i.e. which module?
>
> Generally we try to avoid drivers depending on the specific clocksource,
> so I think there needs to be stronger rationale for exposing this.

I need a system-wide timestamp which can be available from bootloader
and kernel stages including virtual machines.
Actually, it's necessary to record a timestamp of each log message for
system-wide debugging on type-1 hypervisor.
RTC can be used for this purpose but we should make it to hypervisor awareness.
|---------------|-------------------------|
 Bootloader        VM1 (Guest)
                   |-------------------------|
                          VM2 (Guest)

So, the easiest way is using the arm architect timer's timestamp
because it's already supported on each VM by the hypervisor.

Best Regards,
Chanho Park