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

[Sekhar Nori]

Hi Thomas,

On Tuesday 15 December 2015 08:58 PM, Tony Lindgren wrote:
> * Sekhar Nori  [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 
> 
> Looks good to me, probably should get tagged Cc stable when
> committing:
> 
> Acked-by: Tony Lindgren 

Can you please apply this if it looks good?

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

[Tony Lindgren]

* Sekhar Nori  [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 

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

Acked-by: Tony Lindgren 


> ---
> 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_ILR00x0100
>  
>  #define ACTIVEIRQ_MASK   0x7f/* omap2/3 active interrupt 
> bits */
> +#define SPURIOUSIRQ_MASK (0x1ff << 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
> 
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