On 21/05/2019 14:01, Jacky Bai wrote: > >> -----Original Message----- >> From: Daniel Lezcano [mailto:daniel.lezcano@xxxxxxxxxx] >> Sent: Tuesday, May 21, 2019 6:08 PM >> To: Jacky Bai <ping.bai@xxxxxxx>; tglx@xxxxxxxxxxxxx; robh+dt@xxxxxxxxxx; >> shawnguo@xxxxxxxxxx; mark.rutland@xxxxxxx; Aisheng Dong >> <aisheng.dong@xxxxxxx> >> Cc: linux-kernel@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; dl-linux-imx >> <linux-imx@xxxxxxx> >> 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@xxxxxxx> >>> >>> 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). -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog
