[PATCH v6 0/6] ARM: vdso gettimeofday using generic timer architecture

[Stephen Boyd]

On 04/22/14 17:48, Nathan Lynch wrote:
> Provide fast userspace implementations of gettimeofday and
> clock_gettime on systems that implement the generic timers extension
> defined in ARMv7.  This follows the example of arm64 in conception but
> significantly differs in some aspects of the implementation (C vs
> assembly, mainly).
>
> Clocks supported:
> - CLOCK_REALTIME
> - CLOCK_MONOTONIC
> - CLOCK_REALTIME_COARSE
> - CLOCK_MONOTONIC_COARSE
>
> This also provides clock_getres (as arm64 does).
>
> Note that while the high-precision realtime and monotonic clock
> support depends on the generic timers extension, support for
> clock_getres and coarse clocks is independent of the timer
> implementation and is provided unconditionally.

I think we'll need to rename the clocksource in arch_timer.c if we only
have an mmio architected timer to something like arch_mem_counter. Or we
would need to map the register space for the view into userspace? I'm
guessing that is hard, but if that was done then I assume it would lay
the foundation for any mmio clocksource being used for the vdso.

----8<-----
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index b009012429b5..3f3d8ed465f4 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -449,10 +449,12 @@ 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_cp15;
-       else
+       } else {
                arch_timer_read_counter = arch_counter_get_cntvct_mem;
+               clocksource_counter.name = "arch_mem_counter";
+       }
 
        start_count = arch_timer_read_counter();
        clocksource_register_hz(&clocksource_counter, arch_timer_rate);

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