From: Rob Clark <redacted>

Now that we can deal gracefully with bootloader (firmware) initialized
display on aarch64 laptops[1], the next step is to deal with the fact
that the same model of laptop can have one of multiple different panels.
(For the yoga c630 that I have, I know of at least two possible panels,
there might be a third.)

This is actually a scenario that comes up frequently in phones and
tablets as well, so it is useful to have an upstream solution for this.

The basic idea is to add a 'panel-id' property in dt chosen node, and
use that to pick the endpoint we look at when loading the panel driver,
e.g.

/ {
	chosen {
		panel-id = <0xc4>;
	};

	ivo_panel {
		compatible = "ivo,m133nwf4-r0";
		power-supply = <&vlcm_3v3>;
		no-hpd;

		ports {
			port {
				ivo_panel_in_edp: endpoint {
					remote-endpoint = <&sn65dsi86_out_ivo>;
				};
			};
		};
	};

	boe_panel {
		compatible = "boe,nv133fhm-n61";
		power-supply = <&vlcm_3v3>;
		no-hpd;

		ports {
			port {
				boe_panel_in_edp: endpoint {
					remote-endpoint = <&sn65dsi86_out_boe>;
				};
			};
		};
	};

	sn65dsi86: bridge@2c {
		compatible = "ti,sn65dsi86";

		...

		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			...

			port@1 {
				#address-cells = <1>;
				#size-cells = <0>;
				reg = <1>;

				endpoint@c4 {
					reg = <0xc4>;
					remote-endpoint = <&boe_panel_in_edp>;
				};

				endpoint@c5 {
					reg = <0xc5>;
					remote-endpoint = <&ivo_panel_in_edp>;
				};
			};
		};
	}
};

Note that the panel-id is potentially a sparse-int.  The values I've
seen so far on aarch64 laptops are:

  * 0xc2
  * 0xc3
  * 0xc4
  * 0xc5
  * 0x8011
  * 0x8012
  * 0x8055
  * 0x8056

At least on snapdragon aarch64 laptops, they can be any u32 value.

However, on these laptops, the bootloader/firmware is not populating the
chosen node, but instead providing an "UEFIDisplayInfo" variable, which
contains the panel id.  Unfortunately EFI variables are only available
before ExitBootServices, so the second patch checks for this variable
before EBS and populates the /chosen/panel-id variable.

[1] https://patchwork.freedesktop.org/series/63001/

Rob Clark (4):
  dt-bindings: chosen: document panel-id binding
  efi/libstub: detect panel-id
  drm: add helper to lookup panel-id
  drm/bridge: ti-sn65dsi86: use helper to lookup panel-id

 Documentation/devicetree/bindings/chosen.txt | 69 ++++++++++++++++++++
 drivers/firmware/efi/libstub/arm-stub.c      | 49 ++++++++++++++
 drivers/firmware/efi/libstub/efistub.h       |  2 +
 drivers/firmware/efi/libstub/fdt.c           |  9 +++
 drivers/gpu/drm/bridge/ti-sn65dsi86.c        |  5 +-
 drivers/gpu/drm/drm_of.c                     | 21 ++++++
 include/drm/drm_of.h                         |  7 ++
 7 files changed, 160 insertions(+), 2 deletions(-)

-- 
2.20.1

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