Re: Best practice device tree design for display subsystems/DRM

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On 07/04/13 11:30, Sascha Hauer wrote:
On Thu, Jul 04, 2013 at 10:11:31AM +0100, Russell King wrote:
On Thu, Jul 04, 2013 at 10:58:17AM +0200, Sascha Hauer wrote:
On Thu, Jul 04, 2013 at 09:40:52AM +0100, Russell King wrote:
Wrong.  Please read the example with the diagrams I gave.  Consider
what happens if you have two display devices connected to a single
output, one which fixes the allowable mode and one which _can_
reformat the selected mode.

What you describe here is a forced clone mode. This could be described
in the devicetree so that a driver wouldn't start before all connected
displays (links) are present, but this should be limited to the affected
path, not to the whole componentized device.

Okay, to throw a recent argument back at you: so what in this scenario
if you have a driver for the fixed-mode device but not the other device?

It's exactly the same problem which you were describing to Sebastian
just a moment ago with drivers missing from the supernode approach -
you can't start if one of those "forced clone" drivers is missing.

Indeed, then you will see nothing on your display, but I rather make
this setup a special case than the rather usual case that we do not
have compiled in all drivers for all devices referenced in the
supernode.

The super-node links SoC internal devices that do not necessarily match
with the subsystem driver. You have one single DRM driver exploiting
several device nodes for a single video card.

But you need one device node to hook the driver to.

Sebastian

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