From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/2] clocksource: arm_arch_timer: add arch_timer_okay_for_vdso
Date: Mon, 27 Apr 2015 11:55:09 +0100 [thread overview]
Message-ID: <20150427105509.GC1544@arm.com> (raw)
In-Reply-To: <1429911801-6069-1-git-send-email-nathan_lynch@mentor.com>
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
next prev parent reply other threads:[~2015-04-27 10:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-24 21:43 [PATCH 1/2] clocksource: arm_arch_timer: add arch_timer_okay_for_vdso Nathan Lynch
2015-04-24 21:43 ` [PATCH 2/2] ARM: VDSO: use arch_timer_okay_for_vdso Nathan Lynch
2015-04-27 10:55 ` Will Deacon [this message]
2015-04-28 14:08 ` [PATCH 1/2] clocksource: arm_arch_timer: add arch_timer_okay_for_vdso Nathan Lynch
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