From: Mattias Wallin <mattias.wallin@stericsson.com> To: Thomas Gleixner <tglx@linutronix.de> Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Lee Jones <lee.jones@linaro.org> Subject: Re: [PATCH 2/3] clocksource: add DB8500 PRCMU Timer support Date: Tue, 31 May 2011 19:00:39 +0200 [thread overview] Message-ID: <4DE51EB7.7010606@stericsson.com> (raw) In-Reply-To: <alpine.LFD.2.02.1105311236250.3078@ionos> On 05/31/2011 12:38 PM, Thomas Gleixner wrote: > On Tue, 31 May 2011, Mattias Wallin wrote: >> +static cycle_t clksrc_db8500_prcmu_read(struct clocksource *cs) >> +{ >> + u32 count, count2; >> + >> + do { >> + count = readl(PRCMU_TIMER_4_DOWNCOUNT); >> + count2 = readl(PRCMU_TIMER_4_DOWNCOUNT); >> + } while (count2 != count); > > What's the point of this exercise ? It is a software workaround for a HW bug. If the timer is read exactly when the logic is in the process of flipping over to a new value you will get wrong value (large deviations). The problem was found running LTP tests reporting "Timer going backwards". Reading it two times will take long enough for the timer to stabilise according to our HW guys measurements. I agree with you that it is odd enough to deserve a comment in the code. I will comment it in next version. > >> + clocksource_calc_mult_shift(&clocksource_db8500_prcmu, >> + RATE_32K, SCHED_CLOCK_MIN_WRAP); >> + clocksource_register(&clocksource_db8500_prcmu); > > Please use clocksource_register_hz() Ok. > >> diff --git a/include/linux/clksrc-db8500-prcmu.h b/include/linux/clksrc-db8500-prcmu.h >> new file mode 100644 >> index 0000000..42b8587 >> --- /dev/null >> +++ b/include/linux/clksrc-db8500-prcmu.h > > Huch, why needs this to be a separate head in include/linux ? I will move the header file to mach-ux500/include/mach/. Ok? (I have long time ago been thought to avoid include mach headers from the drivers. But if I understand it correct it is not true any more and in this case it certainly makes no sense since I break that rule myself.) > >> @@ -0,0 +1,17 @@ >> +/* >> + * Copyright (C) ST-Ericsson SA 2011 >> + * >> + * License Terms: GNU General Public License v2 >> + * Author: Mattias Wallin<mattias.wallin@stericsson.com> >> + * >> + */ >> +#ifndef __CLKSRC_DB8500_PRCMU_H >> +#define __CLKSRC_DB8500_PRCMU_H >> + >> +#ifdef CONFIG_CLKSRC_DB8500_PRCMU >> +void __init clksrc_db8500_prcmu_init(void); >> +#else >> +void __init clksrc_db8500_prcmu_init(void) {} >> +#endif >> + >> +#endif >> -- >> 1.7.4.3 >> >>
WARNING: multiple messages have this Message-ID (diff)
From: mattias.wallin@stericsson.com (Mattias Wallin) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 2/3] clocksource: add DB8500 PRCMU Timer support Date: Tue, 31 May 2011 19:00:39 +0200 [thread overview] Message-ID: <4DE51EB7.7010606@stericsson.com> (raw) In-Reply-To: <alpine.LFD.2.02.1105311236250.3078@ionos> On 05/31/2011 12:38 PM, Thomas Gleixner wrote: > On Tue, 31 May 2011, Mattias Wallin wrote: >> +static cycle_t clksrc_db8500_prcmu_read(struct clocksource *cs) >> +{ >> + u32 count, count2; >> + >> + do { >> + count = readl(PRCMU_TIMER_4_DOWNCOUNT); >> + count2 = readl(PRCMU_TIMER_4_DOWNCOUNT); >> + } while (count2 != count); > > What's the point of this exercise ? It is a software workaround for a HW bug. If the timer is read exactly when the logic is in the process of flipping over to a new value you will get wrong value (large deviations). The problem was found running LTP tests reporting "Timer going backwards". Reading it two times will take long enough for the timer to stabilise according to our HW guys measurements. I agree with you that it is odd enough to deserve a comment in the code. I will comment it in next version. > >> + clocksource_calc_mult_shift(&clocksource_db8500_prcmu, >> + RATE_32K, SCHED_CLOCK_MIN_WRAP); >> + clocksource_register(&clocksource_db8500_prcmu); > > Please use clocksource_register_hz() Ok. > >> diff --git a/include/linux/clksrc-db8500-prcmu.h b/include/linux/clksrc-db8500-prcmu.h >> new file mode 100644 >> index 0000000..42b8587 >> --- /dev/null >> +++ b/include/linux/clksrc-db8500-prcmu.h > > Huch, why needs this to be a separate head in include/linux ? I will move the header file to mach-ux500/include/mach/. Ok? (I have long time ago been thought to avoid include mach headers from the drivers. But if I understand it correct it is not true any more and in this case it certainly makes no sense since I break that rule myself.) > >> @@ -0,0 +1,17 @@ >> +/* >> + * Copyright (C) ST-Ericsson SA 2011 >> + * >> + * License Terms: GNU General Public License v2 >> + * Author: Mattias Wallin<mattias.wallin@stericsson.com> >> + * >> + */ >> +#ifndef __CLKSRC_DB8500_PRCMU_H >> +#define __CLKSRC_DB8500_PRCMU_H >> + >> +#ifdef CONFIG_CLKSRC_DB8500_PRCMU >> +void __init clksrc_db8500_prcmu_init(void); >> +#else >> +void __init clksrc_db8500_prcmu_init(void) {} >> +#endif >> + >> +#endif >> -- >> 1.7.4.3 >> >>
next prev parent reply other threads:[~2011-05-31 17:01 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-05-31 8:31 [PATCH 2/3] clocksource: add DB8500 PRCMU Timer support Mattias Wallin 2011-05-31 8:31 ` Mattias Wallin 2011-05-31 10:38 ` Thomas Gleixner 2011-05-31 10:38 ` Thomas Gleixner 2011-05-31 17:00 ` Mattias Wallin [this message] 2011-05-31 17:00 ` Mattias Wallin 2011-05-31 21:18 ` Linus Walleij 2011-05-31 21:18 ` Linus Walleij 2011-06-01 7:57 ` Mattias Wallin 2011-06-01 7:57 ` Mattias Wallin 2011-06-01 14:22 ` Mattias Wallin 2011-06-01 14:22 ` Mattias Wallin 2011-06-01 14:25 ` Russell King - ARM Linux 2011-06-01 14:25 ` Russell King - ARM Linux 2011-06-01 14:31 ` Mattias Wallin 2011-06-01 14:31 ` Mattias Wallin 2011-06-01 14:36 ` Mattias Wallin 2011-06-01 14:36 ` Mattias Wallin 2011-06-01 23:35 ` Linus Walleij 2011-06-01 23:35 ` Linus Walleij 2011-06-01 8:30 ` Russell King - ARM Linux 2011-06-01 8:30 ` Russell King - ARM Linux 2011-06-01 8:37 ` Linus Walleij 2011-06-01 8:37 ` Linus Walleij
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