On Fri, Jun 02, 2017 at 06:10:07PM +0800, Chen-Yu Tsai wrote: > The encoder drivers use drm_of_find_possible_crtcs to get upstream > crtcs from the device tree using of_graph. For the results to be > correct, encoders must be probed/bound after _all_ crtcs have been > created. The existing code uses a depth first recursive traversal > of the of_graph, which means the encoders downstream of the TCON > get add right after the first TCON. The second TCON or CRTC will > never be properly associated with encoders connected to it. > > Other platforms, such as Rockchip, deal with this by probing all > crtcs first, then all subsequent components. This is easy to do > since the crtcs correspond to just one device node, and are the > first nodes in the pipeline. > > However with Allwinner SoCs, the function of the CRTC is split between > the display backend (DE 1.0) or mixer (DE 2.0), which does scan-out > and compositing, and the TCON, which generating the display timing > signals. Further complicating the process, there may be a Dynamic Range > Controller between the backend and the TCON. Also, the backend is > preceded by the frontend, with a Display Enhancement Unit possibly > in between. > > One solution would be, instead of a depth first traversal of the > component of_graph, we do a breadth first traversal, so that components > at the same depth are grouped together. This however requires us to > implement extra code for a queue structure that is only used here. > > Instead, since we can identify TCON device nodes, and since the > component system can gracefully deal with duplicate entries, we can add > components in two passes, using the existing recursive depth code. The > first pass stops right after the TCON is added. The second pass will > re-add all components up to the TCON, but these will be skipped since > they will have already been bound with the entries from the first pass. > The encoders added in the second pass will be the last entries in the > list. > > Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx> This commit log is great. So great actually that it should be a comment in the code ;) Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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