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docs/install/e6400.md: Make note of 1440x900 panel errata 

Due to an issue in libgfxinit, Latitude E6400 systems with a 1440 x 900
display panel would have garbled graphics before the OS boots. Make a
note of this issue in releases 20240504 and earlier.

Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
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Nicholas Chin 2024-05-20 11:13:07 -06:00 committed by Leah Rowe
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@ -62,6 +62,19 @@ Intel GPU: libre video initialisation available
Canoeboot uses coreboot's native `libgfxinit` on this platform, for
variants with Intel graphics.
Intel GPU errata
----------------
Systems with a 1440 x 900 display panel instead of the more common 1280 x 800
panel will have garbled graphics before the OS boots (i.e. in SeaBIOS or GRUB)
in Libreboot 20240504 and earlier. This is fixed in releases after 20240504.
This was caused by libgfxinit calculating PLL divider values for the pixel clock
assuming a 96 MHz reference frequency, whereas the E6400 uses a 100 MHz
reference frequency. The error is not large enough to affect the lower
resolution panels, but is enough to affect the 1440 x 900 panels which use a
higher pixel clock.
How to flash internally (no diassembly)
=======================================