On Tue, Mar 28, 2017 at 06:05:08PM +0800, Icenowy Zheng wrote: > > 2017年3月27日 上午5:11于 Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>写道： > > > > 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). > > And from A83T on we will face channel-1 only TCONs., which do not > have channel 0 at all in hardware. Yes, but those patches have not been merged yet, so we don't have to care about the backward compatibility. Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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