Documentation/gfx/display-panel.md

   1 Display Panel Specifics
   2 =======================
   3
   4 Timing Parameters
   5 -----------------
   6
   7 From the binary file `edid` in the sys filesystem on Linux, the panel can be
   8 identified. The exact path may differ slightly. Here is an example:
   9
  10 ```sh
  11 $ strings /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/edid
  12 @0 5
  13 LG Display
  14 LP140WF3-SPD1
  15 ```
  16
  17 To figure out the timing parameters, refer to the [Intel Programmer's Reference
  18 Manuals](https://01.org/linuxgraphics/documentation/hardware-specification-prms)
  19 and try to find the datasheet of the panel using the information from `edid`.
  20 In the example above, you would search for `LP140WF3-SPD1`. Find a table listing
  21 the power sequence timing parameters, which are usually named T[N] and also
  22 referenced in Intel's respective registers listing. You need the values for
  23 `PP_ON_DELAYS`, `PP_OFF_DELAYS` and `PP_DIVISOR` for your `devicetree.cb`:
  24
  25 ```eval_rst
  26 +-----------------------------+---------------------------------------+-----+
  27 | Intel docs                  | devicetree.cb                         | eDP |
  28 +-----------------------------+---------------------------------------+-----+
  29 | Power up delay              | `gpu_panel_power_up_delay`            | T3  |
  30 +-----------------------------+---------------------------------------+-----+
  31 | Power on to backlight on    | `gpu_panel_power_backlight_on_delay`  | T7  |
  32 +-----------------------------+---------------------------------------+-----+
  33 | Power Down delay            | `gpu_panel_power_down_delay`          | T10 |
  34 +-----------------------------+---------------------------------------+-----+
  35 | Backlight off to power down | `gpu_panel_power_backlight_off_delay` | T9  |
  36 +-----------------------------+---------------------------------------+-----+
  37 | Power Cycle Delay           | `gpu_panel_power_cycle_delay`         | T12 |
  38 +-----------------------------+---------------------------------------+-----+
  39 ```
  40
  41 Intel GPU Tools and VBT
  42 -----------------------
  43
  44 The Intel GPU tools are in a package called either `intel-gpu-tools` or
  45 `igt-gpu-tools` in most distributions of Linux-based operating systems.
  46 In the coreboot `util/` directory, you can find `intelvbttool`.
  47
  48 From a running system, you can dump the register values directly:
  49 ```sh
  50 $ intel_reg dump --all | grep PCH_PP
  51                       PCH_PP_STATUS (0x000c7200): 0x80000008
  52                      PCH_PP_CONTROL (0x000c7204): 0x00000007
  53                    PCH_PP_ON_DELAYS (0x000c7208): 0x07d00001
  54                   PCH_PP_OFF_DELAYS (0x000c720c): 0x01f40001
  55                      PCH_PP_DIVISOR (0x000c7210): 0x0004af06
  56 ```
  57
  58 You can obtain the timing values from a VBT (Video BIOS Table), which you can
  59 dump from a vendor UEFI image:
  60 ```sh
  61 $ intel_vbt_decode data.vbt | grep T3
  62                 Power Sequence: T3 2000 T7 10 T9 2000 T10 500 T12 5000
  63                 T3 optimization: no
  64 ```