From mboxrd@z Thu Jan 1 00:00:00 1970 From: sboyd@codeaurora.org (Stephen Boyd) Date: Fri, 29 Aug 2014 13:54:10 -0700 Subject: [PATCH] Doc: dt: arch_timer: discourage clock-frequency use In-Reply-To: <1409251024-19103-1-git-send-email-mark.rutland@arm.com> References: <1409251024-19103-1-git-send-email-mark.rutland@arm.com> Message-ID: <5400E872.2060303@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 > Acked-by: Olof Johansson > Acked-by: Marc Zyngier > Cc: Rob Herring > Cc: Stephen Boyd > Cc: Will Deacon > Cc: Catalin Marinas > Acked-by: Stephen Boyd -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation