lkml.org 
[lkml]   [2015]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] clocksource: arm_arch_timer: add arch_timer_okay_for_vdso
On Fri, Apr 24, 2015 at 10:43:20PM +0100, Nathan Lynch wrote:
> The 32-bit ARM VDSO needs to know whether a generic timer is present
> and whether it is suitable for use by user space. The VDSO
> initialization code currently duplicates some of the logic from the
> driver to make this determination, but unfortunately it is incomplete;
> it will incorrectly enable the VDSO if HYP mode is available or if no
> interrupt is provided for the virtual timer (see arch_timer_init). In
> these cases the driver will switch to memory-backed access while the
> VDSO will attempt to access the counter using cp15 reads.
>
> Add an arch_timer_okay_for_vdso API which can reliably inform the VDSO
> init code whether the arch timer is present and usable.
>
> Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
> ---
> drivers/clocksource/arm_arch_timer.c | 12 ++++++++++++
> include/clocksource/arm_arch_timer.h | 6 ++++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 0aa135ddbf80..b75215523d2f 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -462,6 +462,18 @@ struct timecounter *arch_timer_get_timecounter(void)
> return &timecounter;
> }
>
> +/* The ARM VDSO init code needs to know:
> + * - whether a cp15-based arch timer is present; and if so
> + * - whether the physical or virtual counter is being used.
> + */
> +bool arch_timer_okay_for_vdso(void)
> +{
> + if (!(arch_timers_present & ARCH_CP15_TIMER))
> + return false;
> +
> + return arch_timer_use_virtual;
> +}

If we're adding this, then it wouldn't hurt to use the same check in
arch/arm64 when we update_vsyscall(...). Could we also encapsulate the
`current clocksource' knowledge in there too, to remove the hardcoded
"arch_sys_counter" check from the arch code?

Will


\
 
 \ /
  Last update: 2015-04-27 13:21    [W:0.036 / U:0.628 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site