On Wed, Feb 29, 2012 at 08:35:27PM +0000, Jonathan Cameron wrote:

On 02/29/2012 02:32 PM, Maxime Ripard wrote:

quoted

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.