linux-kernel - Re: [PATCH v2 1/2] ARM: davinci: Allocate extra interrupts

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Message-ID: <0bd745dc-df46-0d37-ed18-b419c1cf2e78@ti.com>
Date:   Fri, 20 Jan 2017 17:20:28 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     David Lechner <david@...hnology.com>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     Kevin Hilman <khilman@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] ARM: davinci: Allocate extra interrupts

On Wednesday 18 January 2017 10:27 PM, David Lechner wrote:
> On 01/18/2017 03:50 AM, Sekhar Nori wrote:
>> On Saturday 14 January 2017 01:30 AM, David Lechner wrote:
>>> This allocates extra interrupts for mach-davinci. These extra interrupts
>>> are need for things like IIO triggers.
>>
>> I am not really familiar with IIO triggers. Can you give some more
>> detail on what fails without this patch?
> 
> A trigger is used to initiate the reading of an iio device. For example,
> there is a mechanism for a sysfs trigger. When you write 1 to the sysfs
> attribute, it triggers an interrupt that is handled by the iio device.
> 
> Since these triggers use interrupts, you need to allocate spare
> interrupts in order to set up the trigger. Otherwise, setting up the
> trigger will fail with an error code (I forgot which one exactly)
> because all of the allocated irqs have already been assigned to hardware
> irqs and are not available.
> 
> Here is where the iio subsytem actually allocates the irq:
> http://lxr.free-electrons.com/source/drivers/iio/industrialio-trigger.c#L525

Alright, I will take a look. Do note that this may not get included in
the first batch of v4.11 changes I queue. But I promise to come back to
it soon afterwards.

Thanks,
Sekhar