linux-kernel - Re: [PATCH 1/3] clocksource: exynos

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Date:	Thu, 19 Jun 2014 10:07:26 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Kukjin Kim <kgene.kim@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Chirantan Ekbote <chirantan@...omium.org>,
	David Riley <davidriley@...omium.org>,
	Olof Johansson <olof@...om.net>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] clocksource: exynos_mct: Fix ftrace

Daniel,

On Tue, Jun 17, 2014 at 5:13 AM, Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
> On 06/04/2014 07:30 PM, Doug Anderson wrote:
>>
>> In (93bfb76 clocksource: exynos_mct: register sched_clock callback) we
>> supported using the MCT as a scheduler clock.  We properly marked
>> exynos4_read_sched_clock() as notrace.  However, we then went and
>> called another function that _wasn't_ notrace.  That means if you do:
>>
>>    cd /sys/kernel/debug/tracing/
>>    echo function_graph > current_tracer
>>
>> You'll get a crash.
>>
>> Fix this (but still let other readers of the MCT be trace-enabled) by
>> adding an extra function.  It's important to keep other users of MCT
>> traceable because the MCT is actually quite slow.
>
>
> Thanks for the explanation in the other email.
>
> I think the last sentence is a bit confusing because you are implicitly
> saying you need these traces to investigate why the timer is slow which is
> referring to something not related to this fix.

Done

>> Signed-off-by: Doug Anderson <dianders@...omium.org>
>> ---
>>   drivers/clocksource/exynos_mct.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/clocksource/exynos_mct.c
>> b/drivers/clocksource/exynos_mct.c
>> index 8d64200..ba3a683 100644
>> --- a/drivers/clocksource/exynos_mct.c
>> +++ b/drivers/clocksource/exynos_mct.c
>> @@ -165,7 +165,7 @@ static void exynos4_mct_frc_start(u32 hi, u32 lo)
>>         exynos4_mct_write(reg, EXYNOS4_MCT_G_TCON);
>>   }
>>
>> -static cycle_t exynos4_frc_read(struct clocksource *cs)
>> +static inline cycle_t notrace _exynos4_frc_read(void)
>
>
> Why inline ?

Somehow I thought that without the "inline" that somehow
exynos4_frc_read() would not be traceable.  ...but this makes no sense
so I've removed.
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