From: Thomas Gleixner <tglx@linutronix.de>
To: Noam Camus <noamc@ezchip.com>
Cc: linux-snps-arc@lists.infradead.org, linux-kernel@vger.kernel.org,
talz@ezchip.com, gilf@ezchip.com, cmetcalf@ezchip.com,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [PATCH v2 03/19] clocksource: Add NPS400 timers driver
Date: Sat, 7 Nov 2015 12:26:10 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1511071222340.4032@nanos> (raw)
In-Reply-To: <1446893557-29748-4-git-send-email-noamc@ezchip.com>
On Sat, 7 Nov 2015, Noam Camus wrote:
> +/*
> + * To get the value from the Global Timer Counter register proceed as follows:
> + * 1. Read the upper 32-bit timer counter register
> + * 2. Read the lower 32-bit timer counter register
> + * 3. Read the upper 32-bit timer counter register again. If the value is
> + * different to the 32-bit upper value read previously, go back to step 2.
> + * Otherwise the 64-bit timer counter value is correct.
> + */
> +static cycle_t nps_clksrc_read(struct clocksource *clksrc)
> +{
> + u64 counter;
> + u32 lower, upper, old_upper;
> + void *lower_p, *upper_p;
> + int cluster = (smp_processor_id() >> NPS_CLUSTER_OFFSET);
> +
> + lower_p = nps_msu_reg_low_addr[cluster];
> + upper_p = lower_p + 4;
> +
> + upper = ioread32be(upper_p);
> + do {
> + old_upper = upper;
> + lower = ioread32be(lower_p);
> + upper = ioread32be(upper_p);
> + } while (upper != old_upper);
> +
> + counter = (upper << 32) | lower;
> + return (cycle_t)counter;
So that clocksource goes up to 1GHz. That means u32 fits ~4.29
seconds. Unless you are striving for NOHZ idle sleep times above that
there is no point in doing that 64bit dance.
The timekeeping code is perfectly fine with a 32bit value. You just
have to set the proper mask.
Thanks,
tglx
next prev parent reply other threads:[~2015-11-07 11:26 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-31 13:15 [PATCH v1 00/20] eznps a new ARC platform Noam Camus
2015-10-31 13:15 ` [PATCH v1 01/20] Documentation: Add EZchip vendor to binding list Noam Camus
2015-10-31 13:15 ` [PATCH v1 02/20] clocksource: Add NPS400 timers driver Noam Camus
2015-11-01 20:44 ` Daniel Lezcano
2015-11-02 7:57 ` Noam Camus
2015-11-02 11:03 ` Vineet Gupta
2015-11-03 15:18 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 03/20] irqchip: add nps Internal and external irqchips Noam Camus
2015-10-31 13:15 ` [PATCH v1 04/20] ARC: Set vmalloc size from configuration Noam Camus
2015-10-31 13:15 ` [PATCH v1 05/20] ARC: rwlock: disable interrupts in !LLSC variant Noam Camus
2015-11-02 9:16 ` Peter Zijlstra
2015-11-02 9:42 ` Vineet Gupta
2015-11-02 10:03 ` Peter Zijlstra
2015-10-31 13:15 ` [PATCH v1 06/20] ARC: Mark cpu online only after it has executed the per cpu init hook Noam Camus
2015-10-31 13:15 ` [PATCH v1 07/20] ARC: mm: use generic macros _BITUL() Noam Camus
2015-11-02 6:23 ` Vineet Gupta
2015-11-02 6:27 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 08/20] ARC: Use res_service as entry point for secondaries Noam Camus
2015-11-02 6:38 ` Vineet Gupta
2015-11-02 8:05 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 09/20] ARC: add CONFIG_CLKSRC_OF support to time_init() Noam Camus
2015-11-02 6:32 ` Vineet Gupta
2015-10-31 13:15 ` [PATCH v1 10/20] ARC: [plat-eznps] Add eznps board defconfig and dts Noam Camus
2015-10-31 13:15 ` [PATCH v1 11/20] ARC: [plat-eznps] Add eznps platform Noam Camus
2015-11-02 10:56 ` Vineet Gupta
2015-11-03 15:59 ` Noam Camus
2015-11-04 12:38 ` Noam Camus
2015-11-05 5:09 ` Vineet Gupta
2015-10-31 13:15 ` [PATCH v1 12/20] ARC: [plat-eznps] Use dedicated user stack top Noam Camus
2015-10-31 13:15 ` [PATCH v1 13/20] ARC: [plat-eznps] Use dedicated bitops/atomic/cmpxchg Noam Camus
2015-11-02 11:56 ` Vineet Gupta
2015-10-31 13:15 ` [PATCH v1 14/20] ARC: [plat-eznps] Use dedicated SMP barriers Noam Camus
2015-11-02 8:02 ` Vineet Gupta
2015-11-02 13:08 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 15/20] ARC: [plat-eznps] Use dedicated identity auxiliary register Noam Camus
2015-10-31 13:15 ` [PATCH v1 16/20] ARC: [plat-eznps] Use dedicated cpu_relax() Noam Camus
2015-11-02 7:54 ` Vineet Gupta
2015-11-02 9:21 ` Peter Zijlstra
2015-11-03 14:02 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 17/20] ARC: [plat-eznps] Use dedicated COMMAND_LINE_SIZE Noam Camus
2015-10-31 13:15 ` [PATCH v1 18/20] ARC: [plat-eznps] define IPI_IRQ Noam Camus
2015-11-02 7:52 ` Vineet Gupta
2015-11-02 12:16 ` Noam Camus
2015-10-31 13:15 ` [PATCH v1 19/20] ARC: [plat-eznps] replace sync with proper cpu barrier Noam Camus
2015-11-02 7:48 ` Vineet Gupta
2015-11-02 9:26 ` Peter Zijlstra
2015-11-17 13:48 ` [PATCH] ARC: remove SYNC from __switch_to() Vineet Gupta
2015-10-31 13:15 ` [PATCH v1 20/20] ARC: Add eznps platform to Kconfig and Makefile Noam Camus
2015-11-02 11:06 ` Vineet Gupta
2015-11-03 15:32 ` Noam Camus
2015-11-04 15:35 ` [PATCH v1 00/20] eznps a new ARC platform Vineet Gupta
2015-11-04 15:53 ` Noam Camus
2015-11-04 17:42 ` Vineet Gupta
2015-11-07 10:52 ` [PATCH v2 00/19] " Noam Camus
2015-11-07 10:52 ` [PATCH v2 01/19] Documentation: Add EZchip vendor to binding list Noam Camus
2015-11-07 10:52 ` [PATCH v2 02/19] ARC: [plat-eznps] define IPI_IRQ Noam Camus
2015-11-07 10:52 ` [PATCH v2 03/19] clocksource: Add NPS400 timers driver Noam Camus
2015-11-07 11:26 ` Thomas Gleixner [this message]
2015-11-20 11:59 ` Noam Camus
2015-11-07 10:52 ` [PATCH v2 04/19] irqchip: add nps Internal and external irqchips Noam Camus
2015-11-07 11:38 ` Thomas Gleixner
2015-11-07 20:52 ` Noam Camus
2015-11-07 23:52 ` Thomas Gleixner
2015-11-07 10:52 ` [PATCH v2 05/19] ARC: Set vmalloc size from configuration Noam Camus
2015-11-07 10:52 ` [PATCH v2 06/19] ARC: rwlock: disable interrupts in !LLSC variant Noam Camus
2015-11-07 10:52 ` [PATCH v2 07/19] ARC: rename smp operation init_irq_cpu() to init_per_cpu() Noam Camus
2015-11-17 11:15 ` Vineet Gupta
2015-11-17 11:38 ` Noam Camus
2015-11-17 11:42 ` Vineet Gupta
2015-11-07 10:52 ` [PATCH v2 08/19] ARC: Mark secondary cpu online only after all HW setup is done Noam Camus
2015-11-17 11:17 ` Vineet Gupta
2015-11-07 10:52 ` [PATCH v2 09/19] ARC: add CONFIG_CLKSRC_OF support to time_init() Noam Camus
2015-11-07 10:52 ` [PATCH v2 10/19] ARC: [plat-eznps] Add eznps board defconfig and dts Noam Camus
2015-11-07 10:52 ` [PATCH v2 11/19] ARC: [plat-eznps] Add eznps platform Noam Camus
2015-11-07 10:52 ` [PATCH v2 12/19] ARC: [plat-eznps] Use dedicated user stack top Noam Camus
2015-11-07 10:52 ` [PATCH v2 13/19] ARC: [plat-eznps] Use dedicated atomic/bitops/cmpxchg Noam Camus
2015-11-07 10:52 ` [PATCH v2 14/19] ARC: [plat-eznps] Use dedicated SMP barriers Noam Camus
2015-11-07 10:52 ` [PATCH v2 15/19] ARC: [plat-eznps] Use dedicated identity auxiliary register Noam Camus
2015-11-07 10:52 ` [PATCH v2 16/19] ARC: [plat-eznps] Use dedicated cpu_relax() Noam Camus
2015-11-09 10:05 ` Peter Zijlstra
2015-11-09 10:22 ` Vineet Gupta
2015-11-09 10:45 ` Peter Zijlstra
2015-11-09 12:27 ` Vineet Gupta
2015-11-09 12:51 ` Peter Zijlstra
2015-11-07 10:52 ` [PATCH v2 17/19] ARC: [plat-eznps] Use dedicated COMMAND_LINE_SIZE Noam Camus
2015-11-07 10:52 ` [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu barrier Noam Camus
2015-11-17 11:12 ` Vineet Gupta
2015-11-17 11:23 ` Peter Zijlstra
2015-11-17 11:37 ` Vineet Gupta
2015-11-17 12:22 ` Peter Zijlstra
2015-11-17 12:37 ` Vineet Gupta
2015-11-17 12:44 ` Peter Zijlstra
2015-11-17 13:32 ` Vineet Gupta
2015-11-17 13:59 ` Peter Zijlstra
2015-11-07 10:52 ` [PATCH v2 19/19] ARC: Add eznps platform to Kconfig and Makefile Noam Camus
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