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viafb: add documentation for proc interface 

This patch adds documentation for the new proc interface that allows
modification of the output device configuration. Should be stable and
useful enough now for daily use.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Cc: Joseph Chan <JosephChan@via.com.tw>
Cc: Andrew Morton <akpm@linux-foundation.org>
hifive-unleashed-5.1
Florian Tobias Schandinat 2010-09-19 05:35:44 +00:00
parent a2aa9f9f5a
commit 47eb1d8417
1 changed files with 48 additions and 0 deletions
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48
Documentation/fb/viafb.txt
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@ -197,6 +197,54 @@ Notes:
example,
# fbset -depth 16
[Configure viafb via /proc]
---------------------------
The following files exist in /proc/viafb
supported_output_devices
This read-only file contains a full ',' seperated list containing all
output devices that could be available on your platform. It is likely
that not all of those have a connector on your hardware but it should
provide a good starting point to figure out which of those names match
a real connector.
Example:
# cat /proc/viafb/supported_output_devices
iga1/output_devices
iga2/output_devices
These two files are readable and writable. iga1 and iga2 are the two
independent units that produce the screen image. Those images can be
forwarded to one or more output devices. Reading those files is a way
to query which output devices are currently used by an iga.
Example:
# cat /proc/viafb/iga1/output_devices
If there are no output devices printed the output of this iga is lost.
This can happen for example if only one (the other) iga is used.
Writing to these files allows adjusting the output devices during
runtime. One can add new devices, remove existing ones or switch
between igas. Essentially you can write a ',' seperated list of device
names (or a single one) in the same format as the output to those
files. You can add a '+' or '-' as a prefix allowing simple addition
and removal of devices. So a prefix '+' adds the devices from your list
to the already existing ones, '-' removes the listed devices from the
existing ones and if no prefix is given it replaces all existing ones
with the listed ones. If you remove devices they are expected to turn
off. If you add devices that are already part of the other iga they are
removed there and added to the new one.
Examples:
Add CRT as output device to iga1
# echo +CRT > /proc/viafb/iga1/output_devices
Remove (turn off) DVP1 and LVDS1 as output devices of iga2
# echo -DVP1,LVDS1 > /proc/viafb/iga2/output_devices
Replace all iga1 output devices by CRT
# echo CRT > /proc/viafb/iga1/output_devices
[Bootup with viafb]:
--------------------
Add the following line to your grub.conf: