linux-kernel - Re: [PATCH] clocksource/arm_arch_timer: Force per-CPU interrupt to trigger on level-high

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Message-ID: <57309030.8040907@arm.com>
Date:	Mon, 9 May 2016 14:27:12 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH] clocksource/arm_arch_timer: Force per-CPU interrupt to
 trigger on level-high

On 09/05/16 14:06, Marc Zyngier wrote:
> The ARM architected timer produces level-triggered interrupts (this
> is mandated by the architecture). Unfortunately, most device-trees
> get this wrong, and expose an edge-triggered interrupt.
> 
> Until now, this wasn't too much an issue, as the programming of the
> trigger would fail (the corresponding PPI cannot be reconfigured),
> and the kernel would be happy with this. But we're about to change
> this, and trust DT a lot if the driver doesn't provide its own
> trigger information. In that context, the timer breaks badly.
> 
> While we do need to fix the DTs, there is also some userspace out
> there (kvmtool) that generates the same kind of broken DT on the
> fly, and that will completely break with newer kernels.
> 
> As a safety measure, and to keep buggy software alive as well as
> buying us some time to fix DTs all over the place, let's enforce
> the interrupt trigger in the timer driver. This doesn't cost
> us anything, and ensures that this will work in all situations,
> broken DT or not.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 5152b38..fdf367ae 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -366,7 +366,7 @@ static int arch_timer_setup(struct clock_event_device *clk)
>  {
>  	__arch_timer_setup(ARCH_CP15_TIMER, clk);
>  
> -	enable_percpu_irq(arch_timer_ppi[arch_timer_uses_ppi], 0);
> +	enable_percpu_irq(arch_timer_ppi[arch_timer_uses_ppi], IRQF_TRIGGER_HIGH);

Looking at it a bit more, it looks like it is should be a TRIGGER_LOW
(the ARM GIC doesn't distinguish between levels, but other
implementations might be able to). Oh well.

I'll respin this shortly.

Thanks,

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