linux-kernel - Re: [PATCH] ASoC: cs35l56: Accept values greater than 0 as IRQ numbers

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Date: Tue, 18 Jun 2024 17:07:59 +0100
From: Richard Fitzgerald <rf@...nsource.cirrus.com>
To: Mark Brown <broonie@...nel.org>
CC: Simon Trimmer <simont@...nsource.cirrus.com>,
        <linux-sound@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>
Subject: Re: [PATCH] ASoC: cs35l56: Accept values greater than 0 as IRQ
 numbers

On 18/06/2024 16:58, Mark Brown wrote:
> On Mon, Jun 17, 2024 at 03:33:59PM +0100, Richard Fitzgerald wrote:
>> On 17/06/2024 15:04, Mark Brown wrote:
> 
>>> Have all architectures removed 0 as a valid IRQ?
> 
>>  From discussion threads we can find 0 might still used on x86 for a
>> legacy device.
> 
> Some of the arm platforms were also an issue in the past, though
> possibly they've all been modernised by now.  Don't know about other
> older architectures.
> 
>> But the conversations we can find on this don't seem to exclude passing
>> a negative error number, just that 0 can normally be assumed invalid.
> 
> Yes, the question was specifically about the assumption that 0 is
> invalid.  The status of 0 is kind of a mess, people keep assuming that
> it isn't valid and it just depends if users of platforms which try to
> use 0 trip up over it.  Sometimes people work on trying to eliminate
> uses of 0 but it tends to get you into older code nobody wants to touch.
> 
>> The kerneldoc for SPI says:
> 
>>   * @irq: Negative, or the number passed to request_irq() to receive
>>   *	interrupts from this device.
> 
> Which includes the 0 as valid thing...
The statement of truth from Linus Torvalds et al. seems to be that 0 is
invalid except on x86. And on x86 it is specifically reserved for a
legacy timer IRQ so it can't be anything else.