linux-kernel - Re: [PATCH v2] clocksource: sun4i: Clear interrupts after stopping timer in probe function

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Date:	Tue, 16 Aug 2016 12:25:16 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Chen-Yu Tsai <wens@...e.org>, Thomas Gleixner <tglx@...utronix.de>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] clocksource: sun4i: Clear interrupts after stopping
 timer in probe function

On 08/15/2016 06:57 AM, Chen-Yu Tsai wrote:
> The bootloader (U-boot) sometimes uses this timer for various delays.
> It uses it as a ongoing counter, and does comparisons on the current
> counter value. The timer counter is never stopped.
> 
> In some cases when the user interacts with the bootloader, or lets
> it idle for some time before loading Linux, the timer may expire,
> and an interrupt will be pending. This results in an unexpected
> interrupt when the timer interrupt is enabled by the kernel, at
> which point the event_handler isn't set yet. This results in a NULL
> pointer dereference exception, panic, and no way to reboot.
> 
> Clear any pending interrupts after we stop the timer in the probe
> function to avoid this.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> ---
> Changes since v1:
> 
>   - Add stable kernel to Cc.
> ---
>  drivers/clocksource/sun4i_timer.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/clocksource/sun4i_timer.c b/drivers/clocksource/sun4i_timer.c
> index 97669ee4df2a..7ab69b36f744 100644
> --- a/drivers/clocksource/sun4i_timer.c
> +++ b/drivers/clocksource/sun4i_timer.c
> @@ -208,6 +208,9 @@ static int __init sun4i_timer_init(struct device_node *node)
>  	/* Make sure timer is stopped before playing with interrupts */
>  	sun4i_clkevt_time_stop(0);
>  
> +	/* clear timer0 interrupt */
> +	writel(0x1, timer_base + TIMER_IRQ_ST_REG);

Can you replace this call with a static inline function and reuse it
also in 'sun4i_timer_interrupt' ?

Thanks.

  -- Daniel



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