HACK: framebuffer scaling for several devices

Add fake panel node for simple-framebuffer to calculate DPI from.
It only needs width & height specified. We can't just reference
"real" panel node which is under mdss/mdp/dsi, because it will
cause simplefb to probe second, after mdss and it will cause
multiple issues.

This fake node allows us to break device link
from simplefb to mdss (implicitly via panel->mdp->mdss) to fix drm
device probe ordering. Without this, simpledrm would probe second
after msm-drm, and confuse userspace with 2 GPUs in /dev/dri.

Alternative workaround is to boot with kernel parameter
`fw_devlink=permissive`, which allows simpledrm to probe first,
but it is worse, because it can hide other issues with device
dependencies.

Author: minlexx

arch/arm64/boot/dts/qcom/sdm660-xiaomi-lavender-common.dtsi

@@ -38,6 +38,23 @@
 			height = <2340>;
 			stride = <(1080 * 4)>;
 			format = "a8r8g8b8";
+
+			/* HACK:
+			 * Fake panel node for simple-framebuffer to calculate DPI from. Only
+			 * needs width & height specified. This allows us to break device link
+			 * from simplefb to mdss (implicitly via panel->mdp->mdss) to fix drm
+			 * device probe ordering. Without this, simpledrm would probe second
+			 * after msm-drm, and confuse userspace with 2 GPUs in /dev/dri.
+			 * Alternative workaround is to boot with kernel parameter
+			 * `fw_devlink=permissive`, which is worse, because it can hide other
+			 * issues with device dependencies.
+			 */
+			panel = <&fb_panel>;
+
+			fb_panel: fb-panel {
+				width-mm = <67>;
+				height-mm = <145>;
+			};
 		};
 	};