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

[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 <nsekhar@ti.com>
---
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	(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+	 * sorting is no longer active during the sorting (10 INTC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 ((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

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

[Felipe Balbi]

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Hi,

Sekhar Nori <nsekhar@ti.com> 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 <nsekhar@ti.com>
> ---
> 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	(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 ((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

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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 <nsekhar@ti.com> 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

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 <nsekhar@ti.com> 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