[PATCH] Doc: dt: arch_timer: discourage clock-frequency use

Stephen Boyd sboyd at codeaurora.org
Fri Aug 29 13:54:10 PDT 2014

On 08/28/14 11:37, Mark Rutland wrote:
> The ARM Generic Timer (AKA the architected timer, arm_arch_timer)
> features a CPU register (CNTFRQ) which firmware is intended to
> initialize, and non-secure software can read to determine the frequency
> of the timer. On CPUs with secure state, this register cannot be written
> from non-secure states.
> The firmware of early SoCs featuring the timer did not correctly
> initialize CNTFRQ correctly on all CPUs, requiring the frequency to be
> described in DT as a workaround. This workaround is not complete however
> as it is exposed to all software in a privileged non-secure mode
> (including guests running under a hypervisor). The firmware and DTs for
> recent SoCs have followed the example set by these early SoCs.
> This patch updates the arch timer binding documentation to make it
> clearer that the use of the clock-frequency property is a poor
> work-around. The MMIO generic timer binding is similarly updated, though
> this is less of a concern as there is generally no need to expose the
> MMIO timers to guest OSs.
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Acked-by: Olof Johansson <olof at lixom.net>
> Acked-by: Marc Zyngier <marc.zyngier at arm.com>
> Cc: Rob Herring <robh+dt at kernel.org>
> Cc: Stephen Boyd <sboyd at codeaurora.org>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>

Acked-by: Stephen Boyd <sboyd at codeaurora.org>

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