Hi Chris, On Wednesday, 3 January 2018 12:09:48 EET Chris Paterson wrote: > Hello Laurent, > > Happy new year! Onnellista uutta vuotta to you too :) > We are looking at upstreaming support for the display provided in the iwg20d > development kit [1]. The setup is slightly unusual in the sense that the > display is an RGB panel (EDT etm070001adh6), connected to the RZ/G1M via an > LVDS/RGB transmitter (DS90CF384AMTDX/NOPB). > > We think that the correct driver to use is > drivers/gpu/drm/panel/panel-lvds.c as as far as the SoC/Kernel is aware > there is an LVDS display connected. However the bindings documentation > states: "compatible: Shall contain "panel-lvds" in addition to a mandatory > panel-specific compatible string defined in individual panel bindings. The > "panel-lvds" value shall never be used on its own." > > As the development kit uses an RGB panel there are no suitable LVDS > panel-specific bindings. Would it be okay in this case to used panel-lvds > on its own? The rationale is that there's no such thing as a fully generic LVDS panel. The panel-lvds compatible string allows supporting panels that are compatible with the interface defined by the panel-lvds driver, but using the compatible string on its own would mean that the operating system would have no way to tweak operation for a particular panel. It might be that using the panel-lvds driver works today, but that you will realize tomorrow that you need some panel-specific quirks. Being able to identify the exact panel model is thus crucial to be future-proof. The exact compatible string for your panel should be "edt,etm070001adh6". Using compatible = "edt,etm070001adh6", "panel-lvds"; will work today and be somehow future-proof, but is a bit of a hack as the panel isn't an LVDS panel. The right solution would be to model the full display pipeline in DT, including the DS90CF384AMTDX. However, the DU driver doesn't support that yet. Some Gen2 boards suffer from a similar issue in the sense that the device tree pretends that a RGB to HDMI encoder is connected directly to the LVDS output of the SoC, while an LVDS to RGB decoder is present in-between. Fixing this is somewhere in my todo list but with a low priority I'm afraid. Would you like to give it a go ? > [1] > http://www.iwavesystems.com/product/development-platform/qseven-evaluation-> board/rz-g1m-qseven-development-kit-49/rz-g1m-qseven-development-kit.html -- Regards, Laurent Pinchart
