linux-kernel - Re: [PATCH v5 7/8] media: i2c: add DS90UB913 driver

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Message-ID: <Y7V/VQAol+pMwKje@pendragon.ideasonboard.com>
Date:   Wed, 4 Jan 2023 15:29:57 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Rosin <peda@...ntia.se>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Shawn Tu <shawnx.tu@...el.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mike Pagano <mpagano@...too.org>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v5 7/8] media: i2c: add DS90UB913 driver

On Tue, Dec 27, 2022 at 10:09:43PM +0200, Andy Shevchenko wrote:
> On Mon, Dec 26, 2022 at 07:01:11PM +0200, Laurent Pinchart wrote:
> > On Wed, Dec 14, 2022 at 08:29:48AM +0200, Tomi Valkeinen wrote:
> > > On 11/12/2022 20:33, Laurent Pinchart wrote:
> > > > On Thu, Dec 08, 2022 at 12:40:05PM +0200, Tomi Valkeinen wrote:
> 
> ...
> 
> > > >> +	dev_dbg(dev, "Bind %s\n", source_subdev->name);
> > > > 
> > > > I'd drop this message.
> 
> +1 here.
> 
> > > Why is that? Do we get this easily from the v4l2 core? These debug 
> > > prints in the bind/unbind process have been valuable for me.
> > 
> > Because debug messages are not meant to be a tracing infrastructure, and
> > because, if we want to keep this message, it would be best handled in
> > the v4l2-async core instead of being duplicated across drivers. Same for
> > the messages at the end of the function.
> 
> I don't think v4l2 needs debug prints. If we consider the above case, the
> ftrace already provides that. If we consider something specific to v4l2 to
> trace only critical parts, then trace events should be implemented.

V4L2 has no support for trace events, and I agree that they would be
useful. It doesn't mean that dev_dbg() is entirely useless though, and
sometimes the line between the two isn't very clear. In any case, for
this very specific debug message, I don't think it should be printed in
individual drivers, but it should be handled in the V4L2 core, either as
a debug message or a trace event.

-- 
Regards,

Laurent Pinchart