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

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Message-ID: <CAHp75VddS225riMvTD36M4UNKC=zKYLCmUdJsACvWbf7=8CqRA@mail.gmail.com>
Date:   Wed, 5 Jan 2022 12:09:08 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sergey Shtylyov <s.shtylyov@....ru>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq() and
 its ilk

On Wed, Jan 5, 2022 at 9:40 AM Sergey Shtylyov <s.shtylyov@....ru> wrote:
> On 12/10/21 2:17 PM, Andy Shevchenko wrote:

> >>> Wanna help?
> >>
> >>    No, I'm afraid you're on your own here...
>
>    Tell me please, how far you've got with this by now?
>    (I've already started to add the fixups to your patch -- unfortunately, this change has to be
> done atomically, not piecemeal.)

I just returned from vacation and will have another one soon, I don't
think I will be doing much for the next couple of weeks.

> >>>> 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().
>
>    I still don't understand why your issue should be fixed 1st -- but I don't really care about
> the order...

See my other comments on the discussion.
The rough roadmap is:
1) check which drivers are still subjects of vIRQ0 which is retrieved
via IRQ resource
2) fix them accordingly (for example, by transforming to IRQ domains)
3) convert platform_get_irq() and Co (including optional variants) to
follow the pattern
 a) non-optional APIs never return 0
 b) optional APIs return negative error, or positive vIRQ or 0 when
IRQ not found

Alternatively you may put a big comment in the drivers first and use
platform_get_resource() for retrieving IRQ0 without WARN(). Then they
will be subject to fix later on.

-- 
With Best Regards,
Andy Shevchenko