[PATCH v8 03/10] clocksource: arm_arch_timer: change clocksource name if CP15 unavailable

[Andy Lutomirski]

On Sun, Aug 3, 2014 at 3:16 AM, Nathan Lynch <nathan_lynch at mentor.com> wrote:
> The arm and arm64 VDSOs need CP15 access to the architected counter.
> If this is unavailable (which is allowed by ARM v7), indicate this by
> changing the clocksource name to "arch_mem_counter" before registering
> the clocksource.
>
> Suggested by Stephen Boyd.
>
> Signed-off-by: Nathan Lynch <nathan_lynch at mentor.com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 5163ec13429d..c99afdf12e98 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -429,11 +429,19 @@ static void __init arch_counter_register(unsigned type)
>         u64 start_count;
>
>         /* Register the CP15 based counter if we have one */
> -       if (type & ARCH_CP15_TIMER)
> +       if (type & ARCH_CP15_TIMER) {
>                 arch_timer_read_counter = arch_counter_get_cntvct;
> -       else
> +       } else {
>                 arch_timer_read_counter = arch_counter_get_cntvct_mem;
>
> +               /* If the clocksource name is "arch_sys_counter" the
> +                * VDSO will attempt to read the CP15-based counter.
> +                * Ensure this does not happen when CP15-based
> +                * counter is not available.
> +                */
> +               clocksource_counter.name = "arch_mem_counter";
> +       }
> +
>         start_count = arch_timer_read_counter();
>         clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>         cyclecounter.mult = clocksource_counter.mult;
> --
> 1.9.3
>

FWIW, x86 does this using the archdata field in the clocksource, but I
see nothing wrong with doing it this way instead.

--Andy