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

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Message-ID: <YbM3T29wPZFLMu1D@smile.fi.intel.com>
Date:   Fri, 10 Dec 2021 13:17:35 +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 Thu, Dec 09, 2021 at 11:21:41PM +0300, Sergey Shtylyov wrote:
> On 12/9/21 11:06 PM, Andy Shevchenko 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
> 
>    I remember that was in your patch that got reverted right after being merged. ;-)
> IMHO returning both error code and 0 on failure is a sign of a misdesigned API, it
> makes the failure check unnecessarily complex and error prone.

I dunno what you are talking about when you mentioned "0 on failure" because 0
is not the failure, that's what I'm trying to tell.

> > 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
> 
>    I don't see much of the discussion there...

Indeed, it was split between two threads. Another one is this:
https://lore.kernel.org/linux-serial/20210407101713.8694-1-andriy.shevchenko@linux.intel.com/T/#u

> > Wanna help?
> 
>    No, I'm afraid you're on your own here... 
> 
> >> Fixes: a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> > 
> > Not sure.
> 
>    Why? It fixes gthe IRQ0 problem, so that you don't have to check for IRQ0 in many callers
> (for the subsytems that treat 0 as s/th special, like polling mode)... If you have something
> to improve, you can do that atop of this patch...

Because first we need to fix all users of platform_get_irq_optional().

-- 
With Best Regards,
Andy Shevchenko