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:   Fri, 12 Jul 2019 11:57:45 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Cheng-Yi Chiang <cychiang@...omium.org>
Cc:     linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        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 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.

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?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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