Re: [PATCH v5 00/23]

From: Russell King - ARM Linux
Date: Sun Feb 02 2014 - 13:24:40 EST

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@xxxxxxxxxxxxxxxx> 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?

> - 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?

FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up. Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".
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