Messages in this thread |  | | Subject | Re: [PATCH v4 2/2] driver: clocksource: Add nxp system counter timer driver support | From | Daniel Lezcano <> | Date | Tue, 21 May 2019 14:20:15 +0200 |
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On 21/05/2019 14:01, Jacky Bai wrote: > >> -----Original Message----- >> From: Daniel Lezcano [mailto:daniel.lezcano@linaro.org] >> Sent: Tuesday, May 21, 2019 6:08 PM >> To: Jacky Bai <ping.bai@nxp.com>; tglx@linutronix.de; robh+dt@kernel.org; >> shawnguo@kernel.org; mark.rutland@arm.com; Aisheng Dong >> <aisheng.dong@nxp.com> >> Cc: linux-kernel@vger.kernel.org; devicetree@vger.kernel.org; dl-linux-imx >> <linux-imx@nxp.com> >> Subject: Re: [PATCH v4 2/2] driver: clocksource: Add nxp system counter timer >> driver support >> >> On 21/05/2019 09:18, Jacky Bai wrote: >>> From: Bai Ping <ping.bai@nxp.com> >>> >>> The system counter (sys_ctr) is a programmable system counter which >>> provides a shared time base to the Cortex A15, A7, A53 etc cores. >>> It is intended for use in applications where the counter is always >>> powered on and supports multiple, unrelated clocks. The sys_ctr >>> hardware >>> supports: >>> - 56-bit counter width (roll-over time greater than 40 years) >> >> The benefit of using more than 32bits on a 32bits system is not proven. >> > > It is mainly used on 64bit ARMv8 system.
Oh, ok. Fair enough.
> >> The function to read and build the 56bits value can have a very significant >> impact on the performance of your platform. >> >> Using a 32bits counter can be enough if it does not wrap too fast. >> >> Can you consider a 32 bits counter ? > > this counter is ARMv8 arch timer's counter source. As it also has timer function, so I choose it > to act as a broadcast timer for cpuidle. The timer interrupt can only be triggered when 'compare[55:0] <= counter[55:0]'. > So you mean that only use the lower 32bit to implement this timer? If so, I can change to use only the lower 32bit.
IMO it is preferable but you decide (probably compare with how long it takes to wrap when 32bits).
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