linux-kernel - Re: [PATCH v6 2/2] drm/i2c:tda998x: Use the HDMI audio CODEC

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Message-ID: <20141001134729.GP5182@n2100.arm.linux.org.uk>
Date:	Wed, 1 Oct 2014 14:47:30 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Mark Brown <broonie@...nel.org>, Dave Airlie <airlied@...il.com>,
	Andrew Jackson <Andrew.Jackson@....com>,
	Jyri Sarha <jsarha@...com>, alsa-devel@...a-project.org,
	devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] drm/i2c:tda998x: Use the HDMI audio CODEC

On Wed, Oct 01, 2014 at 11:28:46AM +0200, Jean-Francois Moine wrote:
> On Tue, 30 Sep 2014 20:25:40 +0100
> Mark Brown <broonie@...nel.org> wrote:
> 
> > > +	request_module("snd-soc-hdmi-codec");
> > > +	pdev = platform_device_register_resndata(&priv->hdmi->dev,
> > > +						 "hdmi-audio-codec",
> > > +						  PLATFORM_DEVID_NONE,
> > > +						  NULL, 0,
> > > +						  &tda998x_hdmi_data,
> > > +						  sizeof tda998x_hdmi_data);  
> > 
> > Why is this request_module() needed?  If there is a good reason for it
> > we should have some documentation.
> 
> The reason is simple: as the HDMI CODEC is not declared in the DT, the
> associated module must be loaded in memory.

Module auto-loading works in non-DT environments too.  Unlike the
direction that the arm port is going, the core kernel features, such
as driver autoloading, are coded *not* to require DT (or indeed any
particular firmware.)

There are circumstances where this has been lost sight of (such as
the gpiod stuff), but as a general rule, features do not rely on DT.

Platform drivers will be auto-loaded if they have:

MODULE_ALIAS(PLATFORM_MODULE_PREFIX DRIVER_NAME);

and DRIVER_NAME matches the non-id part of the platform device name.
In the case of platform driver ID tables:

MODULE_DEVICE_TABLE(platform, id-table);

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