linux-kernel - Re: [PATCH v2] clocksource: exynos

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Message-ID: <53A44D20.2070507@linaro.org>
Date:	Fri, 20 Jun 2014 17:02:56 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Doug Anderson <dianders@...omium.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>
CC:	Vincent Guittot <vincent.guittot@...aro.org>,
	Chirantan Ekbote <chirantan@...omium.org>,
	David Riley <davidriley@...omium.org>, olof@...om.net,
	linux-samsung-soc@...r.kernel.org,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	javier.martinez@...labora.co.uk, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] clocksource: exynos_mct: Fix ftrace

On 06/19/2014 07:08 PM, Doug Anderson wrote:
> In (93bfb76 clocksource: exynos_mct: register sched_clock callback) we
> supported using the MCT as a scheduler clock.

Hi Thomas,

is it possible you update the tip/timers/core so I can get visibility on 
the above patch to apply this one ?

Thanks
   -- Daniel


> 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 to access and we want
> exynos4_frc_read() to show up in ftrace profiles if it's the
> bottleneck.
>
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> Changes in v2:
> - Split out from other patches so this can go into 3.16.
> - Better comment about why exynos4_frc_read() should be traceable.
> - No more useless inline.
>
>   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 f71d55f..5ce99c0 100644
> --- a/drivers/clocksource/exynos_mct.c
> +++ b/drivers/clocksource/exynos_mct.c
> @@ -162,7 +162,7 @@ static void exynos4_mct_frc_start(void)
>   	exynos4_mct_write(reg, EXYNOS4_MCT_G_TCON);
>   }
>
> -static cycle_t exynos4_frc_read(struct clocksource *cs)
> +static cycle_t notrace _exynos4_frc_read(void)
>   {
>   	unsigned int lo, hi;
>   	u32 hi2 = __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_U);
> @@ -176,6 +176,11 @@ static cycle_t exynos4_frc_read(struct clocksource *cs)
>   	return ((cycle_t)hi << 32) | lo;
>   }
>
> +static cycle_t exynos4_frc_read(struct clocksource *cs)
> +{
> +	return _exynos4_frc_read();
> +}
> +
>   static void exynos4_frc_resume(struct clocksource *cs)
>   {
>   	exynos4_mct_frc_start();
> @@ -192,7 +197,7 @@ struct clocksource mct_frc = {
>
>   static u64 notrace exynos4_read_sched_clock(void)
>   {
> -	return exynos4_frc_read(&mct_frc);
> +	return _exynos4_frc_read();
>   }
>
>   static void __init exynos4_clocksource_init(void)
>


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