linux-kernel - Re: [PATCH v2 23/25] tty: serial: samsung_tty: Add earlycon support for Apple UARTs

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Message-ID: <CAK8P3a2mOCfVhR3aeey38sDudJovfz23OOMMHREd8bmy=9-5yw@mail.gmail.com>
Date:   Tue, 16 Feb 2021 11:29:15 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Hector Martin <marcan@...can.st>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Will Deacon <will@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 23/25] tty: serial: samsung_tty: Add earlycon support
 for Apple UARTs

On Tue, Feb 16, 2021 at 11:20 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On Tue, 16 Feb 2021 at 11:19, Arnd Bergmann <arnd@...nel.org> wrote:
> > > > +     return samsung_early_console_setup(device, opt);
> > >
> > > Don't you need to handle the error code - set PROT_DEFAULT() or whatever
> > > was there before?
> >
> > __set_fixmap() has no return value, it just writes a page table entry and
> > does not fail.
>
> I meant, handle samsung_early_console_setup() error code (NULL).

Ah, I see.

I don't think it makes a difference -- if ->setup() fails, the page table entry
is just left in place unused, and the type of the unused mapping doesn't
matter. If earlycon tried to unmap the page, the type also would not
change anything.

With earlycon, I'd generally lean towards keeping things as simple as possible,
in order to increase the chance of seeing anything at all. It clearly wouldn't
hurt to try to add minimal error handling here.

       Arnd