Documentation: arm64: Document PMU counters access from userspace
Add documentation to describe the access to the pmu hardware counters from userspace. Signed-off-by: Raphael Gault <raphael.gault@arm.com> Signed-off-by: Rob Herring <robh@kernel.org> Link: https://lore.kernel.org/r/20211208201124.310740-6-robh@kernel.org Signed-off-by: Will Deacon <will@kernel.org>