Date: Sun, 2 Feb 2014 19:54:00 +0100
From: Jean-Francois Moine <moinejf@free.fr>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: dri-devel@lists.freedesktop.org, Dave Airlie <airlied@gmail.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Rob Clark <robdclark@gmail.com>
Subject: Re: [PATCH v5 00/23]
Message-ID: <20140202195400.073f4eb4@armhf>
In-Reply-To: <20140202182349.GJ26684@n2100.arm.linux.org.uk>
References: <cover.1390986082.git.moinejf@free.fr>
	<20140202124358.GD26684@n2100.arm.linux.org.uk>
	<20140202190606.6fa193ce@armhf>
	<20140202182349.GJ26684@n2100.arm.linux.org.uk>
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Sender: linux-kernel-owner@vger.kernel.org

On Sun, 2 Feb 2014 18:23:49 +0000
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> On Sun, Feb 02, 2014 at 07:06:06PM +0100, Jean-Francois Moine wrote:
> > On Sun, 2 Feb 2014 12:43:58 +0000
> > Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
> > 
> > > On Wed, Jan 29, 2014 at 10:01:22AM +0100, Jean-Francois Moine wrote:
> > > > This patch set contains various extensions to the tda998x driver:
> > > > 
> > > > - simplify the i2c read/write
> > > > - code cleanup and fix some small errors
> > > > - use global constants
> > > > - don't read write-only registers
> > > > - add DT support
> > > > - use IRQ for connection status and EDID read
> > > 
> > > I discussed these patches with Rob Clark recently, and the conclusion
> > > we came to is that I'll merge them into a git tree, test them, and
> > > once I'm happy I'll send a pull request as appropriate.
> > > 
> > > I'll go through them later today.  Those patches which have been re-
> > > posted without any change for the last few times (the first few) I'll
> > > take into my git tree today so you don't have to keep re-posting them
> > > (more importantly, I won't have to keep on looking at them either.)
> > 
> > Thanks.
> > 
> > BTW, I found some problems with the patch 12 'add DT support' you
> > already acked:
> > 
> > - the .of_match_table is not needed because the i2c client is created by
> >   the i2c subsystem from the 'reg' in the DT,
> 
> Okay - may it be a good idea to have someone knowledgable of I2C give it
> a review?

Sure! There is still a lot of magic in the DT.

I used the tda998x in the DT for a long time without .of_match_table
and it loaded correctly. I added it in the patch just because my other
modules had it.

A few days ago, when I moved the tda998x audio codec description in the
DT as a subnode of the tda998x i2c, the codec module was not loaded. An
of_platform_populate() of the subnodes was needed in the tda998x i2c
driver. I could not find why...

> > - on encoder_destroy(), the function drm_i2c_encoder_destroy()
> >   unregisters the i2c client, so, with a DT, a second encoder_init()
> >   would crash.
> 
> I think this is one of the down-sides of trying to bolt DT into this:
> the drm encoder slave support is not designed to cope with an i2c client
> device pre-created.
> 
> In fact, I can't see how this stuff comes anywhere close to working in
> a DT setup: in such a scenario, you declare that there's a tda998x
> device in DT.  I2C parses this, and creates an i2c_client itself for
> the tda998x.
> 
> When the TDA998x driver initialises, it finds this i2c client and
> binds to it, calling tda998x_probe(), which does nothing.
> 
> However, the only way to attach a slave encoder to a DRM device is via
> a call to drm_i2c_encoder_init(), which unconditionally calls
> i2c_new_device().  This creates a _new_ i2c_client structure, again
> unconditionally, for the tda998x.  This must be bound by the I2C
> subsystem to a driver - hopefully the tda998x driver, which then
> calls it's encoder_init function.
> 
> None of this will happen if DT has already created an i2c_client at
> the appropriate address, because DRMs i2c_new_device() will fail.
> 
> My hypothesis is that you have other patches to I2C and/or DRM to
> sort this out which you haven't been posting with this series.  So,
> could you please provide some hints as to how this works?

I explained how to use the tda998x in a DT context in a message to Jyri
Sarha:

http://lists.freedesktop.org/archives/dri-devel/2014-January/052936.html

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/
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