[Openchrome-devel] [Bug 91966] No signal to monitor with X and openchrome using VX855 chipset graphics

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Sun Nov 1 20:47:30 PST 2015


--- Comment #47 from Kevin Brace <kevinbrace at gmx.com> ---
(In reply to Christopher from comment #46)

Hi Christopher,

> Kevin, would you have the expertise to repair the UMS issues within the
> driver? I'll gladly test if you can code.

Many years back when I was a kid, I have done direct VGA register programming
in MS-DOS and x86 assembly language, in order to write a game.
I still do remember some aspects of it.
2 months ago when I was trying to fix the standby mode resume LCD issue (ACPI
S3 State or STR resume), I did read through VX800, VX855, and VX900 technical
documentation, and worked mainly on via_vgahw.c.
The functions that save and restore VIA Technologies extended VGA registers
were broken (i.e., Many registers were not being saved when they should have
been saved.), and in particular, the code was not fully saving many VGA
registers for UniChrome Pro and Chrome 9.
I completely rewrote the save and restore function, but this still did not
resolve the LCD screen functionality getting lost when my VN896 chipset-based
laptop resumes from STR (The LCD screen is restored okay if I use hibernation,
Probably some other portion of the OpenChrome UMS code is handling display
controller reinitialization, so I need to look into understanding the code
paths that handle this.
Since the my current code does not really resolve the matter, there is no
official patch for this rewrite at this point.
I sent the code sample to Xavier Bachelot, but due to various first time
developer issues  has not accepted the changes yet.
Right now, I am trying to figure out how to create a patch for some other
change I made to the OpenChrome code that Xavier did not really like (Sorry, I
am not trying to annoy Xavier, but as a first step, just want to start cleaning
up the OpenChrome code. This update did not alter the functionality of the
device driver.)
    Anyway, I obviously cannot promise when a patch to fix the VX855 display
controller initialization can be ready, but I will start reading the UMS
display management code (via_ums.c) right now after I finish writing this
e-mail so that I can start understanding what is going on inside UMS display
management code.
>From reading VX855 graphics hardware programming documentation, generally
speaking, the display controller portion is very similar to VX800 graphics.
There was a lot of changes made between VX855 and VX900 (VX900 graphics
supports HDMI and DisplayPort, in addition to the legacy stuff like VGA. That
being said, the HDMI display controller programming information is somehow
missing. The programming information for DisplayPort is properly provided.), so
I am myself surprised that the code "broke" with VX855.


Kevin Brace

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