Re: [PATCH v3] irqchip: omap-intc: add support for spurious irq handling

[Tony Lindgren <tony@atomide.com>]

* Sekhar Nori <nsekhar@ti.com> [151215 06:26]:
> Under some conditions, irq sorting procedure used
> by INTC can go wrong resulting in a spurious irq
> getting reported.
> 
> If this condition is not handled, it results in
> endless stream of:
> 
>     unexpected IRQ trap at vector 00
> 
> messages from ack_bad_irq()
> 
> Handle the spurious interrupt condition in omap-intc
> driver to prevent this.
> 
> Measurements using kernel function profiler on AM335x
> EVM running at 720MHz show that after this patch
> omap_intc_handle_irq() takes about 37.4us against
> 34us before this patch.
> 
> Signed-off-by: Sekhar Nori <nsekhar@ti.com>

Looks good to me, probably should get tagged Cc stable when
committing:

Acked-by: Tony Lindgren <tony@atomide.com>


> ---
> v3: add unlikely(), add profiling information
>     to commit message.
> 
> v2: increment error irq counter, use pr_err_once,
>     add a comment on tips to debug spurious irq
>     condition.
> 
> This patch results in a checkpatch warning about
> extern definition of irq_err_count, but looks like
> thats the prevalent method of accessing that counter.
> 
>  drivers/irqchip/irq-omap-intc.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-omap-intc.c b/drivers/irqchip/irq-omap-intc.c
> index 8587d0f8d8c0..f6cb1b8bb981 100644
> --- a/drivers/irqchip/irq-omap-intc.c
> +++ b/drivers/irqchip/irq-omap-intc.c
> @@ -47,6 +47,7 @@
>  #define INTC_ILR0		0x0100
>  
>  #define ACTIVEIRQ_MASK		0x7f	/* omap2/3 active interrupt bits */
> +#define SPURIOUSIRQ_MASK	(0x1ffffff << 7)
>  #define INTCPS_NR_ILR_REGS	128
>  #define INTCPS_NR_MIR_REGS	4
>  
> @@ -330,11 +331,35 @@ static int __init omap_init_irq(u32 base, struct device_node *node)
>  static asmlinkage void __exception_irq_entry
>  omap_intc_handle_irq(struct pt_regs *regs)
>  {
> +	extern unsigned long irq_err_count;
>  	u32 irqnr;
>  
>  	irqnr = intc_readl(INTC_SIR);
> +
> +	/*
> +	 * A spurious IRQ can result if interrupt that triggered the
> +	 * sorting is no longer active during the sorting (10 INTC
> +	 * functional clock cycles after interrupt assertion). Or a
> +	 * change in interrupt mask affected the result during sorting
> +	 * time. There is no special handling required except ignoring
> +	 * the SIR register value just read and retrying.
> +	 * See section 6.2.5 of AM335x TRM Literature Number: SPRUH73K
> +	 *
> +	 * Many a times, a spurious interrupt situation has been fixed
> +	 * by adding a flush for the posted write acking the IRQ in
> +	 * the device driver. Typically, this is going be the device
> +	 * driver whose interrupt was handled just before the spurious
> +	 * IRQ occurred. Pay attention to those device drivers if you
> +	 * run into hitting the spurious IRQ condition below.
> +	 */
> +	if (unlikely((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK)) {
> +		pr_err_once("%s: spurious irq!\n", __func__);
> +		irq_err_count++;
> +		omap_ack_irq(NULL);
> +		return;
> +	}
> +
>  	irqnr &= ACTIVEIRQ_MASK;
> -	WARN_ONCE(!irqnr, "Spurious IRQ ?\n");
>  	handle_domain_irq(domain, irqnr, regs);
>  }
>  
> -- 
> 2.6.3
>