# 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:

    $ 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 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`:

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:

    $ 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:

    $ intel_vbt_decode data.vbt | grep T3
                    Power Sequence: T3 2000 T7 10 T9 2000 T10 500 T12 5000
                    T3 optimization: no