On Fri, Mar 17, 2017 at 11:34:45AM +0800, Chen-Yu Tsai wrote:
On Thu, Mar 16, 2017 at 1:37 AM, Rob Herring robh@kernel.org wrote:
On Tue, Mar 07, 2017 at 09:56:26AM +0100, Maxime Ripard wrote:
The Allwinner Timings Controller has two, mutually exclusive, channels. When the binding has been introduced, it was assumed that there would be only a single user per channel in the system.
While this is likely for the channel 0 which only connects to LCD displays, it turns out that the channel 1 can be connected to multiple controllers in the SoC (HDMI and TV encoders for example). And while the simultaneous use of HDMI and TV outputs cannot be achieved, switching from one to the other at runtime definitely sounds plausible.
Add an extra property, allwinner,tcon-channel, to specify for a given endpoint which TCON channel it is connected to, while falling back to the previous mechanism if that property is missing.
I think perhaps TCON channels should have been ports rather than endpoints. The fact that the channels are mutually exclusive can be handled in the driver and doesn't really matter in the binding. How painful would it be to rework things to move TCON channel 1 from port 0, endpoint 1 to port 1?
Having a separate output port for channel 1 was one option we discussed. However it wouldn't work well with the kernel's of_graph based crtc detection (drm_of_find_possible_crtcs / drm_of_find_possible_crtcs), which has the crtcs bound via the output port. As the logic is used by multiple drivers, I'm not sure it's easy to rework or test.
Can't we use a different logic than drm_of_find_possible_crtcs to fill the same role?
Also, we still have to support old device trees using channel 1 from output port 0 endpoint 1. This is the TV encoder on sun5i (A10s/A13/R8).
We could probably work something out if we go that way to deal with old DTs though.
Maxime