Daniel Maslowski has uploaded this change for review.

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Documentation: libgfxinit timing parameters

Change-Id: I94c2784ffcc12f54c285e1f90d73ff3905c4fae7
Signed-off-by: Daniel Maslowski <daniel.maslowski@img.ly>
---
M Documentation/gfx/libgfxinit.md
1 file changed, 29 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/46/33246/1

diff --git a/Documentation/gfx/libgfxinit.md b/Documentation/gfx/libgfxinit.md
index c50761a..c19b10b 100644
--- a/Documentation/gfx/libgfxinit.md
+++ b/Documentation/gfx/libgfxinit.md
@@ -125,3 +125,32 @@
 given order until all available pipes are taken. That's 1 pipe
 in VGA textmode, 2 pipes in high-resolution mode until Sandy
 Bridge, 3 pipes from Ivy Bridge on.
+
+GMA: 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`:
+
+|Intel docs                 |devicetree.cb                         |Haswell |
+|---------------------------|--------------------------------------|--------|
+|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` |T7      |
+|Power Cycle Delay          |`gpu_panel_power_cycle_delay`         |T12     |

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