linux-kernel - Re: [PATCH] ARM: arch timer: Set the TVAL before timer is enabled

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Message-ID: <51C80D07.2020106@arm.com>
Date:	Mon, 24 Jun 2013 10:10:31 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Rohit Vaswani <rvaswani@...eaurora.org>
CC:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: arch timer: Set the TVAL before timer is enabled

On 21/06/13 21:31, Rohit Vaswani wrote:
> On some hardware, the timer deasserts the interrupt when a
> new TVAL is written only when the enable bit is cleared.
> Hence explicitly disable the timer and then program the
> TVAL followed by enabling the timer.
> If this order is not followed, there are chances that
> you would not receive any timer interrupts.
> This is done as suggested in https://lkml.org/lkml/2012/8/11/39
> 
> Signed-off-by: Rohit Vaswani <rvaswani@...eaurora.org>
> ---
>  drivers/clocksource/arm_arch_timer.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index a2b2541..05ba0c2 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -103,9 +103,10 @@ static inline void set_next_event(const int access, unsigned long evt)
>  {
>  	unsigned long ctrl;
>  	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL);
> -	ctrl |= ARCH_TIMER_CTRL_ENABLE;
> -	ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
> +	ctrl &= ~(ARCH_TIMER_CTRL_ENABLE | ARCH_TIMER_CTRL_IT_MASK);
> +	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl);
>  	arch_timer_reg_write(access, ARCH_TIMER_REG_TVAL, evt);
> +	ctrl |= ARCH_TIMER_CTRL_ENABLE;
>  	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl);
>  }

Maybe that would deserve a comment in the code so people don't get the
idea it can be reordered to save the extra write?

Other than that, and FWIW:
Acked-by: Marc Zyngier <marc.zyngier@....com>

	M.
-- 
Jazz is not dead. It just smells funny...

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