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-rw-r--r--Documentation/gfx/display-panel.md64
-rw-r--r--Documentation/gfx/libgfxinit.md3
2 files changed, 67 insertions, 0 deletions
diff --git a/Documentation/gfx/display-panel.md b/Documentation/gfx/display-panel.md
new file mode 100644
index 0000000000..3bab0896fd
--- /dev/null
+++ b/Documentation/gfx/display-panel.md
@@ -0,0 +1,64 @@
+Display Panel Specifics
+=======================
+
+Timing Parameters
+-----------------
+
+From the binary file `edid` in the sys filesystem on Linux, the panel can be
+identified. The exact path may differ slightly. Here is an example:
+
+```sh
+$ strings /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/edid
+@0 5
+LG Display
+LP140WF3-SPD1
+```
+
+To figure out the timing parameters, refer to the [Intel Programmer's Reference
+Manuals](https://01.org/linuxgraphics/documentation/hardware-specification-prms)
+and try to find the datasheet of the panel using the information from `edid`.
+In the example above, you would search for `LP140WF3-SPD1`. Find a table listing
+the power sequence timing parameters, which are usually named T[N] and also
+referenced in Intel's respective registers listing. You need the values for
+`PP_ON_DELAYS`, `PP_OFF_DELAYS` and `PP_DIVISOR` for your `devicetree.cb`:
+
+```eval_rst
++-----------------------------+---------------------------------------+-----+
+| Intel docs | devicetree.cb | eDP |
++-----------------------------+---------------------------------------+-----+
+| Power up delay | `gpu_panel_power_up_delay` | T3 |
++-----------------------------+---------------------------------------+-----+
+| Power on to backlight on | `gpu_panel_power_backlight_on_delay` | T7 |
++-----------------------------+---------------------------------------+-----+
+| Power Down delay | `gpu_panel_power_down_delay` | T10 |
++-----------------------------+---------------------------------------+-----+
+| Backlight off to power down | `gpu_panel_power_backlight_off_delay` | T9 |
++-----------------------------+---------------------------------------+-----+
+| Power Cycle Delay | `gpu_panel_power_cycle_delay` | T12 |
++-----------------------------+---------------------------------------+-----+
+```
+
+Intel GPU Tools and VBT
+-----------------------
+
+The Intel GPU tools are in a package called either `intel-gpu-tools` or
+`igt-gpu-tools` in most distributions of Linux-based operating systems.
+In the coreboot `util/` directory, you can find `intelvbttool`.
+
+From a running system, you can dump the register values directly:
+```sh
+$ intel_reg dump --all | grep PCH_PP
+ PCH_PP_STATUS (0x000c7200): 0x80000008
+ PCH_PP_CONTROL (0x000c7204): 0x00000007
+ PCH_PP_ON_DELAYS (0x000c7208): 0x07d00001
+ PCH_PP_OFF_DELAYS (0x000c720c): 0x01f40001
+ PCH_PP_DIVISOR (0x000c7210): 0x0004af06
+```
+
+You can obtain the timing values from a VBT (Video BIOS Table), which you can
+dump from a vendor UEFI image:
+```sh
+$ intel_vbt_decode data.vbt | grep T3
+ Power Sequence: T3 2000 T7 10 T9 2000 T10 500 T12 5000
+ T3 optimization: no
+```
diff --git a/Documentation/gfx/libgfxinit.md b/Documentation/gfx/libgfxinit.md
index c50761a14e..c000f27d60 100644
--- a/Documentation/gfx/libgfxinit.md
+++ b/Documentation/gfx/libgfxinit.md
@@ -55,6 +55,9 @@ follows:
GMA: Per Board Configuration
----------------------------
+In order to set up the display panel, see the
+[display panel-specific documentation](/gfx/display-panel.md).
+
There are a few Kconfig symbols to consider. To indicate that a
board can initialize graphics through *libgfxinit*: