IIO irq allocation fails on AT91SAM9G45

IIO irq allocation fails on AT91SAM9G45

[Maxime Ripard]

Hi everyone,

I'm working on adding the support for the AT91SAM9M10G45-EK board from
Atmel for the at91_adc driver I previously posted, and I encounter some
weird issue here.

When calling the iio_allocate_trigger
(http://lxr.free-electrons.com/source/drivers/staging/iio/industrialio-trigger.c?a=arm#L421)
from my driver on the G45, it returns ENOMEM, while on the
AT91SAM9G20-EK board, it works perfectly.

Digging a bit into it, it seems that the call to irq_alloc_descs is
returning the error (the value of CONFIG_IIO_CONSUMERS_PER_TRIGGER is 2
in my configuration, which seems pretty reasonable and is the default
value anyway), which is itself getting that return value from
irq_expand_nr_irqs.

Here, I'm left confused, I don't know this part of the kernel anymore,
and most importantly, it seems to be pretty-much arch-independant, while
the nature of my issue seems really platform-dependant.

Do you have any clue of what's going on here ?

Thanks,
-- 
Maxime Ripard, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

IIO irq allocation fails on AT91SAM9G45

[Jonathan Cameron]

On 02/29/2012 02:32 PM, Maxime Ripard wrote:
> Hi everyone,
> 
> I'm working on adding the support for the AT91SAM9M10G45-EK board from
> Atmel for the at91_adc driver I previously posted, and I encounter some
> weird issue here.
> 
> When calling the iio_allocate_trigger
> (http://lxr.free-electrons.com/source/drivers/staging/iio/industrialio-trigger.c?a=arm#L421)
> from my driver on the G45, it returns ENOMEM, while on the
> AT91SAM9G20-EK board, it works perfectly.
> 
> Digging a bit into it, it seems that the call to irq_alloc_descs is
> returning the error (the value of CONFIG_IIO_CONSUMERS_PER_TRIGGER is 2
> in my configuration, which seems pretty reasonable and is the default
> value anyway), which is itself getting that return value from
> irq_expand_nr_irqs.
> 
> Here, I'm left confused, I don't know this part of the kernel anymore,
> and most importantly, it seems to be pretty-much arch-independant, while
> the nature of my issue seems really platform-dependant.
> 
> Do you have any clue of what's going on here ?
We ran into this originally on the pxa as well.   My guess is that
nr_irqs is not set high enough for that particular board.

Looking back I can find some mention of a nasty bit of code that
just adds a bit of padding but I can't find it now.

Anyhow, you probably have a line somewhere in the kernel log
saying something like:

[    0.000000] NR_IRQS:288 nr_irqs:296 296

NR_IRQS is typically the number of the SoC
nr_irqs should be large enough to accomodate those provided by
other peripherals.

I also have a vague recollection that the problem goes away entirely
with sparse irqs?

Michael, you commented on this issue originally, can you remember
any more details than me? (It seemed like I wrote plenty at the
time but I can't for the life of me fill in the missing details!)

IIO irq allocation fails on AT91SAM9G45

[Russell King - ARM Linux]

On Wed, Feb 29, 2012 at 08:35:27PM +0000, Jonathan Cameron wrote:
> On 02/29/2012 02:32 PM, Maxime Ripard wrote:
> > Hi everyone,
> > 
> > I'm working on adding the support for the AT91SAM9M10G45-EK board from
> > Atmel for the at91_adc driver I previously posted, and I encounter some
> > weird issue here.
> > 
> > When calling the iio_allocate_trigger
> > (http://lxr.free-electrons.com/source/drivers/staging/iio/industrialio-trigger.c?a=arm#L421)
> > from my driver on the G45, it returns ENOMEM, while on the
> > AT91SAM9G20-EK board, it works perfectly.
> > 
> > Digging a bit into it, it seems that the call to irq_alloc_descs is
> > returning the error (the value of CONFIG_IIO_CONSUMERS_PER_TRIGGER is 2
> > in my configuration, which seems pretty reasonable and is the default
> > value anyway), which is itself getting that return value from
> > irq_expand_nr_irqs.
> > 
> > Here, I'm left confused, I don't know this part of the kernel anymore,
> > and most importantly, it seems to be pretty-much arch-independant, while
> > the nature of my issue seems really platform-dependant.
> > 
> > Do you have any clue of what's going on here ?
> We ran into this originally on the pxa as well.   My guess is that
> nr_irqs is not set high enough for that particular board.
> 
> Looking back I can find some mention of a nasty bit of code that
> just adds a bit of padding but I can't find it now.
> 
> Anyhow, you probably have a line somewhere in the kernel log
> saying something like:
> 
> [    0.000000] NR_IRQS:288 nr_irqs:296 296
> 
> NR_IRQS is typically the number of the SoC
> nr_irqs should be large enough to accomodate those provided by
> other peripherals.
> 
> I also have a vague recollection that the problem goes away entirely
> with sparse irqs?

Yes, because IRQs will be allocated above the last figure on that
line, up to IRQ_BITMAP_BITS which happens to be 8192 above NR_IRQS.

There's an issue though: if your on-SoC IRQ controller is already
using irq_alloc_descs(), it will fail if you want it to grab IRQs
below the last figure on that line, because those will have already
been allocated for you.

IIO irq allocation fails on AT91SAM9G45

[Maxime Ripard]

Le 29/02/2012 21:48, Russell King - ARM Linux a ?crit :
> On Wed, Feb 29, 2012 at 08:35:27PM +0000, Jonathan Cameron wrote:
>> On 02/29/2012 02:32 PM, Maxime Ripard wrote:
>>> Hi everyone,
>>>
>>> I'm working on adding the support for the AT91SAM9M10G45-EK board from
>>> Atmel for the at91_adc driver I previously posted, and I encounter some
>>> weird issue here.
>>>
>>> When calling the iio_allocate_trigger
>>> (http://lxr.free-electrons.com/source/drivers/staging/iio/industrialio-trigger.c?a=arm#L421)
>>> from my driver on the G45, it returns ENOMEM, while on the
>>> AT91SAM9G20-EK board, it works perfectly.
>>>
>>> Digging a bit into it, it seems that the call to irq_alloc_descs is
>>> returning the error (the value of CONFIG_IIO_CONSUMERS_PER_TRIGGER is 2
>>> in my configuration, which seems pretty reasonable and is the default
>>> value anyway), which is itself getting that return value from
>>> irq_expand_nr_irqs.
>>>
>>> Here, I'm left confused, I don't know this part of the kernel anymore,
>>> and most importantly, it seems to be pretty-much arch-independant, while
>>> the nature of my issue seems really platform-dependant.
>>>
>>> Do you have any clue of what's going on here ?
>> We ran into this originally on the pxa as well.   My guess is that
>> nr_irqs is not set high enough for that particular board.
>>
>> Looking back I can find some mention of a nasty bit of code that
>> just adds a bit of padding but I can't find it now.
>>
>> Anyhow, you probably have a line somewhere in the kernel log
>> saying something like:
>>
>> [    0.000000] NR_IRQS:288 nr_irqs:296 296
>>
>> NR_IRQS is typically the number of the SoC
>> nr_irqs should be large enough to accomodate those provided by
>> other peripherals.
>>
>> I also have a vague recollection that the problem goes away entirely
>> with sparse irqs?
> 
> Yes, because IRQs will be allocated above the last figure on that
> line, up to IRQ_BITMAP_BITS which happens to be 8192 above NR_IRQS.
> 
> There's an issue though: if your on-SoC IRQ controller is already
> using irq_alloc_descs(), it will fail if you want it to grab IRQs
> below the last figure on that line, because those will have already
> been allocated for you.

Ok, so using either the sparse irqs or changing the definition of
NR_IRQS from 192 to 224 makes the problem go away.

I guess the reason because I was not seeing this issue with the G20 is
because it has less interrupt sources.

Anyway, I'm not sure about the augmenting the NR_IRQS fix. It seems to
work pretty well, but might it have some weird side-effects ?

Should I send a patch for it, or should I find another way to fix this ?

-- 
Maxime Ripard, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com