From: shinya.kuribayashi.px@renesas•com (Shinya Kuribayashi)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2 2/2] ARM: delay: allow timer-based delay implementation to be selected
Date: Tue, 17 Jul 2012 16:42:36 +0900 [thread overview]
Message-ID: <5005176C.6050904@renesas.com> (raw)
In-Reply-To: <CAMQu2gx9EU4GZ634RKiwD+sg0MoO-FAqc-pPU+HkryX8rXVBjA@mail.gmail.com>
On 7/17/2012 3:11 PM, Shilimkar, Santosh wrote:
> Thanks for the detailed explanation. CPU clock detection is indeed the
> nit way to skip the calibration overhead and this was one of the comment
> when I tried to push the skipping of calibration for secondary CPUs.
>
> Looks like you have a working patch for the clock detection. Will
> you able to post that patch so that this long pending calibration
> for secondary CPUs gets optimized.
Something like this should work (not even build tested, can be applied
on top of Will's v2 patchset):
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index e1030e1..736dcea 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -25,6 +25,8 @@
#include <linux/module.h>
#include <linux/timex.h>
+static unsigned long lpj_early;
+
/*
* Default to the loop-based delay implementation.
*/
@@ -59,8 +61,22 @@ void __init init_current_timer_delay(unsigned long freq)
{
pr_info("Switching to timer-based delay loop\n");
lpj_fine = freq / HZ;
+ lpj_early = lpj_fine;
+ loops_per_jiffy = lpj_fine;
arm_delay_ops.delay = __timer_delay;
arm_delay_ops.const_udelay = __timer_const_udelay;
arm_delay_ops.udelay = __timer_udelay;
}
+
+void __cpuinit calibrate_delay_early(unsigned long cpu_freq)
+{
+ lpj_early = (cpu_freq + HZ/2) / HZ;
+ loops_per_jiffy = lpj_early;
+ pr_info("Calibrating delay using CPU frequency.. %lu Hz\n", cpu_freq);
+}
+
+unsigned long __cpuinit calibrate_delay_is_known(void)
+{
+ return lpj_early; /* this function works for both UP/SMP cases */
+}
#endif
And change your ->timer() func (called via time_init) to make use of it:
unsigned long freq;
/* For UP/SMP systems */
freq = get_CPU_frequency();
calibrate_delay_early(freq);
#ifdef CONFIG_SMP
/* For SMP systems */
freq = get_Timer_frequency();
init_current_timer_delay(freq);
#endif
The way to detect CPU clock speed can vary depending on your systems,
so hard to be generalized. In my case, I have full-blown clock tree
described for my SoCs, and the CPU clock speed can be easily obtained
by clk_get_rate("xxx").
Hope this helps!
--
Shinya Kuribayashi
Renesas Electronics
next prev parent reply other threads:[~2012-07-17 7:42 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-29 17:33 [PATCH v2 0/2] Use architected timers for delay loop Will Deacon
2012-06-29 17:33 ` [PATCH v2 1/2] ARM: arch timer: implement read_current_timer and get_cycles Will Deacon
2012-07-02 19:14 ` Stephen Boyd
2012-07-05 12:35 ` Shinya Kuribayashi
2012-07-05 12:59 ` Will Deacon
2012-06-29 17:33 ` [PATCH v2 2/2] ARM: delay: allow timer-based delay implementation to be selected Will Deacon
2012-07-02 19:14 ` Stephen Boyd
2012-07-02 21:53 ` Will Deacon
2012-07-03 12:09 ` Shinya Kuribayashi
2012-07-04 15:36 ` Will Deacon
2012-07-05 12:12 ` Shinya Kuribayashi
2012-07-05 12:56 ` Will Deacon
2012-07-05 16:51 ` Stephen Boyd
2012-07-05 13:06 ` Shinya Kuribayashi
2012-07-05 14:15 ` Will Deacon
2012-07-12 7:33 ` Shinya Kuribayashi
2012-07-12 8:44 ` Will Deacon
2012-07-12 9:35 ` Shinya Kuribayashi
2012-07-12 16:40 ` Stephen Boyd
2012-07-13 2:16 ` Shinya Kuribayashi
2012-07-13 8:57 ` Will Deacon
2012-07-13 10:48 ` Shilimkar, Santosh
2012-07-13 11:13 ` Will Deacon
2012-07-13 12:04 ` Shilimkar, Santosh
2012-07-13 12:08 ` Will Deacon
2012-07-13 12:14 ` Shilimkar, Santosh
2012-07-13 12:23 ` Will Deacon
2012-07-13 12:28 ` Shilimkar, Santosh
2012-07-17 3:10 ` Shinya Kuribayashi
2012-07-17 6:11 ` Shilimkar, Santosh
2012-07-17 7:42 ` Shinya Kuribayashi [this message]
2012-07-17 9:05 ` Will Deacon
2012-07-19 12:43 ` Shinya Kuribayashi
2012-07-18 17:52 ` Will Deacon
2012-07-19 15:19 ` Jonathan Austin
2012-07-20 10:17 ` Will Deacon
2012-07-24 9:06 ` Shinya Kuribayashi
2012-07-24 9:15 ` Will Deacon
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