linux-kernel - Re: [PATCH v3 1/5] ASoC: hdmi-codec: Add an op to set callback function for plug event

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Date:   Mon, 15 Jul 2019 23:56:19 +0800
From:   Tzung-Bi Shih <tzungbi@...gle.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Cheng-Yi Chiang <cychiang@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ALSA development <alsa-devel@...a-project.org>,
        Douglas Anderson <dianders@...omium.org>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-rockchip@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>, tzungbi@...omium.org,
        Jaroslav Kysela <perex@...ex.cz>,
        Hans Verkuil <hverkuil@...all.nl>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Mark Brown <broonie@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel@...ll.ch>, dgreid@...omium.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/5] ASoC: hdmi-codec: Add an op to set callback
 function for plug event

On Fri, Jul 12, 2019 at 6:58 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Fri, Jul 12, 2019 at 06:04:39PM +0800, Cheng-Yi Chiang wrote:
> > Add an op in hdmi_codec_ops so codec driver can register callback
> > function to handle plug event.
> >
> > Driver in DRM can use this callback function to report connector status.
> >
> > Signed-off-by: Cheng-Yi Chiang <cychiang@...omium.org>
> > ---
> >  include/sound/hdmi-codec.h    | 16 +++++++++++++
> >  sound/soc/codecs/hdmi-codec.c | 45 +++++++++++++++++++++++++++++++++++
> >  2 files changed, 61 insertions(+)
> >
> > diff --git a/include/sound/hdmi-codec.h b/include/sound/hdmi-codec.h
> > index 7fea496f1f34..9a8661680256 100644
> > --- a/include/sound/hdmi-codec.h
> > +++ b/include/sound/hdmi-codec.h
> > @@ -47,6 +47,9 @@ struct hdmi_codec_params {
> >       int channels;
> >  };
> >
> > +typedef void (*hdmi_codec_plugged_cb)(struct device *dev,
> > +                                   bool plugged);
> > +
>
> I'd like to pose a question for people to think about.
>
> Firstly, typedefs are generally shunned in the kernel.  However, for
> these cases it seems to make sense.
>
> However, should the "pointer"-ness be part of the typedef or not?  To
> see what I mean, consider:
>
>         typedef void (*hdmi_foo)(void);
>
>         int register_foo(hdmi_foo foo);
>
> vs
>
>         typedef void hdmi_foo(void);
>
>         int register_foo(hdmi_foo *foo);
>
> which is more in keeping with how we code non-typedef'd code - it's
> obvious that foo is a pointer while reading the code.
I have a different opinion.  Its suffix "_cb" self-described it is a
callback function.  Since function and function pointer are equivalent
in the language, I think we don't need to emphasize that it is a
function "pointer".


> It seems to me that the latter better matches what is in the kernel's
> coding style, which states:
>
>   In general, a pointer, or a struct that has elements that can
>   reasonably be directly accessed should **never** be a typedef.
>
> or maybe Documentation/process/coding-style.rst needs updating?