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@xxxxxxxxxx> 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 -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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