* Sekhar Nori <nsekhar@xxxxxx> [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@xxxxxx>
Looks good to me, probably should get tagged Cc stable when
committing:
Acked-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
> 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 + * sorting is no longer active during the sorting (10 INTC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
>
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