From: shawn.guo@linaro.org (Shawn Guo)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] clocksource: vf_pit_timer: use complement for sched_clock reading
Date: Thu, 6 Mar 2014 09:45:36 +0800 [thread overview]
Message-ID: <20140306014530.GA11366@S2101-09.ap.freescale.net> (raw)
In-Reply-To: <d25af915993aec1b486be653eb86f748ddef54fe.1394057313.git.stefan@agner.ch>
On Wed, Mar 05, 2014 at 11:11:08PM +0100, Stefan Agner wrote:
> Vybrids PIT register is monitonic decreasing. However, sched_clock
> reading needs to be monitonic increasing. Use bitwise not to get
> the complement of the clock register. This fixes the clock going
> backward. Also, the clock now starts at 0 since we load the
> register with the maximum value at start.
>
> Signed-off-by: Stefan Agner <stefan@agner.ch>
Looks correct to me, so
Acked-by: Shawn Guo <shawn.guo@linaro.org>
But I also copied the driver author Jingchang to see if he has any
comment.
Shawn
> ---
> drivers/clocksource/vf_pit_timer.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/vf_pit_timer.c b/drivers/clocksource/vf_pit_timer.c
> index 02821b0..a918bc4 100644
> --- a/drivers/clocksource/vf_pit_timer.c
> +++ b/drivers/clocksource/vf_pit_timer.c
> @@ -54,7 +54,7 @@ static inline void pit_irq_acknowledge(void)
>
> static u64 pit_read_sched_clock(void)
> {
> - return __raw_readl(clksrc_base + PITCVAL);
> + return ~__raw_readl(clksrc_base + PITCVAL);
> }
>
> static int __init pit_clocksource_init(unsigned long rate)
> --
> 1.9.0
>
next prev parent reply other threads:[~2014-03-06 1:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-05 22:11 [PATCH] clocksource: vf_pit_timer: use complement for sched_clock reading Stefan Agner
2014-03-06 1:45 ` Shawn Guo [this message]
2014-03-06 3:18 ` Jingchang Lu
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