From mboxrd@z Thu Jan 1 00:00:00 1970 From: sboyd@codeaurora.org (Stephen Boyd) Date: Thu, 24 Apr 2014 10:00:14 -0700 Subject: [PATCH v6 0/6] ARM: vdso gettimeofday using generic timer architecture In-Reply-To: <535876D1.8040609@mentor.com> References: <53581865.2020601@codeaurora.org> <535876D1.8040609@mentor.com> Message-ID: <5359431E.8050108@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 04/23/14 19:28, Nathan Lynch wrote: > On 04/23/2014 02:45 PM, Stephen Boyd wrote: >> On 04/22/14 17:48, Nathan Lynch wrote: >>> Provide fast userspace implementations of gettimeofday and >>> clock_gettime on systems that implement the generic timers extension >>> defined in ARMv7. This follows the example of arm64 in conception but >>> significantly differs in some aspects of the implementation (C vs >>> assembly, mainly). >>> >>> Clocks supported: >>> - CLOCK_REALTIME >>> - CLOCK_MONOTONIC >>> - CLOCK_REALTIME_COARSE >>> - CLOCK_MONOTONIC_COARSE >>> >>> This also provides clock_getres (as arm64 does). >>> >>> Note that while the high-precision realtime and monotonic clock >>> support depends on the generic timers extension, support for >>> clock_getres and coarse clocks is independent of the timer >>> implementation and is provided unconditionally. >> I think we'll need to rename the clocksource in arch_timer.c if we only >> have an mmio architected timer to something like arch_mem_counter. > I guess ARMv7 would allow you to have mmio without cp15 (AFAIK ARMv8 > does not). I don't see any dts in arch/arm that contains an > arm,armv7-timer-mem node without an arm,armv7-timer node, though. I only know of an ARMv7 device that is like this but the support for it isn't in linus' tree. > If this is a practical concern, I think using > CONFIG_ARCH_CLOCKSOURCE_DATA is perhaps a better way to communicate > whether cp15 access is available. That's how the x86 vdso, for example, > decides between using HPET vs TSC etc. > I don't quite follow why it's any better than changing the string because we only really care about using cp15. If we cared about using cp15 vs mmio it might make sense. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation