Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay
From: Daniel Lezcano
Date: Thu Jun 19 2014 - 06:30:47 EST
On 06/19/2014 12:21 PM, amit daniel kachhap wrote:
On Thu, Jun 19, 2014 at 2:41 PM, Daniel Lezcano
<daniel.lezcano@xxxxxxxxxx> wrote:
On 06/19/2014 10:39 AM, Amit Daniel Kachhap wrote:
This patch register the exynos mct clocksource as the current timer
as it has constant clock rate. This will generate correct udelay for the
exynos platform and avoid using unnecessary calibrated jiffies. This
change
has been tested on exynos5420 based board and udelay is very close to
expected.
Signed-off-by: Amit Daniel Kachhap <amit.daniel@xxxxxxxxxxx>
---
Changes in V2:
* Added #defines for ARM and ARM64 as pointed by Doug Anderson.
Patches from David Riley confirmed that udelay is broken in exynos5420.
Link to those patches are,
1) https://patchwork.kernel.org/patch/4344911/
2) https://patchwork.kernel.org/patch/4344881/
drivers/clocksource/exynos_mct.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/drivers/clocksource/exynos_mct.c
b/drivers/clocksource/exynos_mct.c
index f71d55f..02927e2 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -195,10 +195,25 @@ static u64 notrace exynos4_read_sched_clock(void)
return exynos4_frc_read(&mct_frc);
}
+static struct delay_timer exynos4_delay_timer;
+
+static unsigned long exynos4_read_current_timer(void)
+{
+#ifdef ARM
+ return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);
+#else /* ARM64, etc */
+ return exynos4_frc_read(&mct_frc);
+#endif
+}
+
There isn't another solution than that ? macros definitions in C file are
avoided as much as possible.
I also didn't want to use macros but used as a last option. you want
me to put more comments here?
Or something like below is also possible for checking the size of
(unsigned long) in runtime.
unsigned long x;
unsigned int size = (char *)(&x + 1) - (char *)(&x);
if (size == 4)
return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);
else
return exynos4_frc_read(&mct_frc);
But this involves extra computation which should not be used for time
critical functions.
Any suggestion?
AFAIU, Doug may change the exynos4_frc_read to be 32 bits. So may not
need those macros as 'exynos4_frc_read' could be used instead.
Doug may confirm this.
static void __init exynos4_clocksource_init(void)
{
exynos4_mct_frc_start();
+ exynos4_delay_timer.read_current_timer =
&exynos4_read_current_timer;
&exynos4_read_current_timer ?
Any issue in the naming?
No problem with the naming. As Tomasz pointed also, you are passing '&'
for the function pointer.
+ exynos4_delay_timer.freq = clk_rate;
+ register_current_timer_delay(&exynos4_delay_timer);
+
if (clocksource_register_hz(&mct_frc, clk_rate))
panic("%s: can't register clocksource\n", mct_frc.name);
--
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