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

Re: 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!)

Re: 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.

Re: IIO irq allocation fails on AT91SAM9G45

[Maxime Ripard]

Le 29/02/2012 21:48, Russell King - ARM Linux a =E9crit :
> 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 f=
rom
>>> 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/industria=
lio-trigger.c?a=3Darm#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 defau=
lt
>>> 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 anymo=
re,
>>> 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?
>=20
> 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.
>=20
> 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 =
?

--=20
Maxime Ripard, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com