Re: [PATCH v6 01/10] arm64: pmu: Add function implementation to update event index in userpage

[Will Deacon]

On Wed, Mar 10, 2021 at 05:08:28PM -0700, Rob Herring wrote:
> From: Raphael Gault <raphael.gault@xxxxxxx>
> 
> In order to be able to access the counter directly for userspace,
> we need to provide the index of the counter using the userpage.
> We thus need to override the event_idx function to retrieve and
> convert the perf_event index to armv8 hardware index.
> 
> Since the arm_pmu driver can be used by any implementation, even
> if not armv8, two components play a role into making sure the
> behaviour is correct and consistent with the PMU capabilities:
> 
> * the ARMPMU_EL0_RD_CNTR flag which denotes the capability to access
> counter from userspace.
> * the event_idx call back, which is implemented and initialized by
> the PMU implementation: if no callback is provided, the default
> behaviour applies, returning 0 as index value.
> 
> Signed-off-by: Raphael Gault <raphael.gault@xxxxxxx>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/perf_event.c | 18 ++++++++++++++++++
>  include/linux/perf/arm_pmu.h   |  2 ++
>  2 files changed, 20 insertions(+)

Acked-by: Will Deacon <will@xxxxxxxxxx>

Will