linux-kernel - Re: [PATCH] platform: finally disallow IRQ0 in platform_get

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Date:   Thu, 9 Dec 2021 22:06:19 +0200
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Sergey Shtylyov <s.shtylyov@....ru>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq()
 and its ilk

On Sat, Nov 06, 2021 at 11:26:47PM +0300, Sergey Shtylyov wrote:
> The commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is
> invalid") only calls WARN() when IRQ0 is about to be returned, however
> using IRQ0 is considered invalid (according to Linus) outside the arch/
> code where it's used by the i8253 drivers. Many driver subsystems treat
> 0 specially (e.g. as an indication of the polling mode by libata), so
> the users of platform_get_irq[_byname]() in them would have to filter
> out IRQ0 explicitly and this (quite obviously) doesn't scale...
> Let's finally get this straight and return -EINVAL instead of IRQ0!

You are changing the return value of platform_get_irq_optional().
The problem here is the proposed change doesn't bring any value in such
case. platform_get_irq_optional() should be able (at the end of the day)
to return 3 types of values (as other APIs do):
	 > 0: success
	== 0: IRQ not found
	 < 0: an error that must be consumed by the caller

0 is unexpected result for non-optional APIs and there you may try to play
tricks (like replacing it by error code).

There was a discussion around the topic:
https://lore.kernel.org/lkml/20210331144526.19439-1-andriy.shevchenko@linux.intel.com/T/#u

Wanna help?

> Fixes: a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")

Not sure.

-- 
With Best Regards,
Andy Shevchenko