65 lines
2.8 KiB
Markdown
65 lines
2.8 KiB
Markdown
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Display Panel Specifics
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=======================
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Timing Parameters
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-----------------
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From the binary file `edid` in the sys filesystem on Linux, the panel can be
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identified. The exact path may differ slightly. Here is an example:
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```sh
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$ strings /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/edid
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@0 5
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LG Display
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LP140WF3-SPD1
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```
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To figure out the timing parameters, refer to the [Intel Programmer's Reference
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Manuals](https://01.org/linuxgraphics/documentation/hardware-specification-prms)
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and try to find the datasheet of the panel using the information from `edid`.
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In the example above, you would search for `LP140WF3-SPD1`. Find a table listing
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the power sequence timing parameters, which are usually named T[N] and also
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referenced in Intel's respective registers listing. You need the values for
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`PP_ON_DELAYS`, `PP_OFF_DELAYS` and `PP_DIVISOR` for your `devicetree.cb`:
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```eval_rst
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+-----------------------------+---------------------------------------+-----+
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| Intel docs | devicetree.cb | eDP |
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+-----------------------------+---------------------------------------+-----+
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| Power up delay | `gpu_panel_power_up_delay` | T3 |
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+-----------------------------+---------------------------------------+-----+
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| Power on to backlight on | `gpu_panel_power_backlight_on_delay` | T7 |
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+-----------------------------+---------------------------------------+-----+
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| Power Down delay | `gpu_panel_power_down_delay` | T10 |
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+-----------------------------+---------------------------------------+-----+
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| Backlight off to power down | `gpu_panel_power_backlight_off_delay` | T9 |
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+-----------------------------+---------------------------------------+-----+
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| Power Cycle Delay | `gpu_panel_power_cycle_delay` | T12 |
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+-----------------------------+---------------------------------------+-----+
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```
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Intel GPU Tools and VBT
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-----------------------
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The Intel GPU tools are in a package called either `intel-gpu-tools` or
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`igt-gpu-tools` in most distributions of Linux-based operating systems.
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In the coreboot `util/` directory, you can find `intelvbttool`.
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From a running system, you can dump the register values directly:
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```sh
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$ intel_reg dump --all | grep PCH_PP
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PCH_PP_STATUS (0x000c7200): 0x80000008
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PCH_PP_CONTROL (0x000c7204): 0x00000007
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PCH_PP_ON_DELAYS (0x000c7208): 0x07d00001
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PCH_PP_OFF_DELAYS (0x000c720c): 0x01f40001
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PCH_PP_DIVISOR (0x000c7210): 0x0004af06
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```
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You can obtain the timing values from a VBT (Video BIOS Table), which you can
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dump from a vendor UEFI image:
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```sh
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$ intel_vbt_decode data.vbt | grep T3
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Power Sequence: T3 2000 T7 10 T9 2000 T10 500 T12 5000
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T3 optimization: no
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```
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