linux-kernel - Re: [PATCH v4 2/4] drm/panel: jdi-lpm102a188a: Fix bug and clean up driver

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Message-ID: <CAD=FV=Xbijn6j9Oxc88k3iq+wSF9bV76X6uw4ADWWxwR+q=o0w@mail.gmail.com>
Date: Mon, 21 Jul 2025 08:46:59 -0700
From: Doug Anderson <dianders@...omium.org>
To: Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>
Cc: Brigham Campbell <me@...ghamcampbell.com>, tejasvipin76@...il.com, 
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev, 
	dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <jessica.zhang@....qualcomm.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH v4 2/4] drm/panel: jdi-lpm102a188a: Fix bug and clean up driver

Hi,

On Sun, Jul 20, 2025 at 4:19 AM Diogo Ivo <diogo.ivo@...nico.ulisboa.pt> wrote:
>
> On 7/20/25 8:50 AM, Brigham Campbell wrote:
> > On Sat Jul 19, 2025 at 11:10 AM MDT, Diogo Ivo wrote:
> >>> nit: can just be this:
> >>>
> >>> struct mipi_dsi_multi_context dsi_ctx = {};
> >>
> >> I am not an expert here but I was under the impression that this is only
> >> valid with C23 while the kernel is written in C11. Is there something I
> >> am missing?
> >>
> >> Diogo
> >
> > You're right, C23 was the first standard to bless the usage of the empty
> > initializer, ` = {};`, but if I'm right, it's been a GNU extension long
> > before C11. At risk of being pedantic, I'll draw attention to line 580
> > of the kernel's root Makefile:
> >
> > KBUILD_CFLAGS += -std=gnu11
> >
> > The kernel is technically written in the GNU variant of C11, extensions
> > and all. In fact, the first patch of this series uses optional variadic
> > macro arguments, which aren't a part of any official C standard as far
> > as I'm aware.
> >
> > In any case, a simple grep for some forms of the empty initializer shows
> > usages all over the drm subsystem.
> >
> > That said, I don't know if GNU extensions are formally documented or
> > where one would look for that information. Importantly, I am by far the
> > junior as far as kernel coding is concerned. I yield to your experience
> > and I'm happy to change this initialization in v6 if that's best.
>
> I found the documentation here [1], and it does state regarding designated
> initializers that "Omitted fields are implicitly initialized the same as for
> objects that have static storage duration." so I take it that no v6 is
> needed :)
>
> Diogo
>
> [1]:
> https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated-Inits

Right. I think the key here is (as Brigham said) `git grep '= {}'`
shows countless hits in the kernel. :-) ...so we're not introducing
any new compiler requirement here with your patch. ;-)

-Doug