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

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Message-ID: <139f2c33-7fb3-3a63-6dfe-caa2cca500ce@ti.com>
Date:   Thu, 2 Feb 2017 20:36:06 +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 Friday 20 January 2017 11:47 PM, David Lechner wrote:
> On 01/20/2017 05:50 AM, Sekhar Nori wrote:
>> 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.
>>
> 
> It is not critical at this point, so it is fine to wait a bit.

So, I think instead of increasing NR_IRQS by a small number, we should 
instead shift to use SPARSE_IRQ. I looked at some patches from Tony 
Lindgren converting OMAP1 to use SPARSE_IRQ. There is some work 
involved, but it does not look to be too huge a change to me.

685e2d08c54b ARM: OMAP1: Change interrupt numbering for sparse IRQ
b694331cfb2e ARM: omap1: Switch to use MULTI_IRQ
55b447744389 ARM: OMAP1: Switch to use generic irqchip in preparation for sparse IRQ
928f81aa619d ARM: OMAP1: Move UART defines to prepare for sparse IRQ

Thanks,
Sekhar