[PATCH 3/9] Doc/DT: Add DT binding documentation for DVI Connector

[Daniel Vetter]

On Fri, Feb 28, 2014 at 04:23:27PM +0000, Russell King - ARM Linux wrote:
> On Fri, Feb 28, 2014 at 06:12:23PM +0200, Tomi Valkeinen wrote:
> > On 28/02/14 17:59, Russell King - ARM Linux wrote:
> > 
> > >> +dvi0: connector at 0 {
> > >> +	compatible = "dvi-connector";
> > >> +	label = "dvi";
> > >> +
> > >> +	i2c-bus = <&i2c3>;
> > >> +
> > >> +	dvi_connector_in: endpoint {
> > >> +		remote-endpoint = <&tfp410_out>;
> > >> +	};
> > >> +};
> > > 
> > > This looks far too simplistic.  There are different classes of DVI
> > > connector - there is:
> > > 
> > > DVI A - analogue only
> > > DVI D - digital only (single and dual link)
> > > DVI I - both (single and dual digital link)
> > > 
> > > DRM at least makes a distinction between these three classes, and this
> > > disctinction is part of the user API.  How would a display system know
> > > which kind of DVI connector is wired up on the board from this DT
> > > description?
> > 
> > Yes, I think that's a valid change. But do we also need to specify
> > single/dual link, in addition to the three types?
> 
> I would argue that as it's a difference in physical hardware, then it
> should be described in DT, even if we don't use it.  The reasoning is
> that although we may not use it today, we may need to use it in the
> future, and as we're describing what the hardware actually is - and
> even in this case what pins may be present or missing on the connector,
> it's unlikely to be problematical (the only problem is when someone
> omits it...)

If you plug a dual-link dvi screen into a soc which can do dual-link but
the actual connector is cheap and doesn't have this wired up
(differentiate wtf) then the kernel needs to know. Otherwise it can't
correctly filter out the modes with dotclocks high enough to require dual
link and the user will look at a black screen.

3.14 has a regression in drm/i915 where we've screwed this up ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch