Re: [PATCH v2] irqchip: omap-intc: add support for spurious irq handling

[Sekhar Nori]

On Thursday 10 December 2015 08:46 PM, Sekhar Nori wrote:
> Hi Felipe,
> 
> On Tuesday 08 December 2015 07:15 PM, Felipe Balbi wrote:
>> Sekhar Nori  writes:
> 
>>> +   /*
>>> +* 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 +* sorting is no longer active during the sorting (10 INTC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 ((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK) {
>>
>> sounds like unlikely() wouldn't hurt here.
> 
> I can add, but looks like it does not make a big difference. See below.
> 
>>
>>> +   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);
>>
>> care to run kernel function profiler against omap_intc_handle_irq()
>> before and after this patch ?
> 
> Before this patch I see average running time time of 34us. That
> increases to 37.8us after this patch. With unlikely() the number I got
> was 37.4us. So the benefit with unlikely() is in the noise range.
> 
> This was using AM335x EVM at 720 MHz.

Just sent a v3 with unlikely() and profiling information added to commit
message.

Thanks,
Sekhar
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH v2] irqchip: omap-intc: add support for spurious irq handling

[Sekhar Nori]

Hi Felipe,

On Tuesday 08 December 2015 07:15 PM, Felipe Balbi wrote:
> Sekhar Nori  writes:

>> +/*
>> + * 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 + * sorting is no longer active during the sorting (10 INTC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 ((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK) {
> 
> sounds like unlikely() wouldn't hurt here.

I can add, but looks like it does not make a big difference. See below.

> 
>> +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);
> 
> care to run kernel function profiler against omap_intc_handle_irq()
> before and after this patch ?

Before this patch I see average running time time of 34us. That
increases to 37.8us after this patch. With unlikely() the number I got
was 37.4us. So the benefit with unlikely() is in the noise range.

This was using AM335x EVM at 720 MHz.

Thanks,
Sekhar
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH v2] irqchip: omap-intc: add support for spurious irq handling

[Sekhar Nori]

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.

Signed-off-by: Sekhar Nori 
---
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..639708de5529 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   (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 ((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

--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH v2] irqchip: omap-intc: add support for spurious irq handling

[Felipe Balbi]

Hi,

Sekhar Nori  writes:
> 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.
>
> Signed-off-by: Sekhar Nori 
> ---
> 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..639708de5529 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 ((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK) {

sounds like unlikely() wouldn't hurt here.

> + 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);

care to run kernel function profiler against omap_intc_handle_irq()
before and after this patch ?

-- 
balbi


signature.asc
Description: PGP signature