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-rw-r--r--Documentation/fb/udlfb.txt39
1 files changed, 27 insertions, 12 deletions
diff --git a/Documentation/fb/udlfb.txt b/Documentation/fb/udlfb.txt
index 7fdde2a..57d2f29 100644
--- a/Documentation/fb/udlfb.txt
+++ b/Documentation/fb/udlfb.txt
@@ -87,23 +87,38 @@ Special configuration for udlfb is usually unnecessary. There are a few
options, however.
From the command line, pass options to modprobe
-modprobe udlfb defio=1 console=1
+modprobe udlfb fb_defio=0 console=1 shadow=1
-Or for permanent option, create file like /etc/modprobe.d/options with text
-options udlfb defio=1 console=1
+Or modify options on the fly at /sys/module/udlfb/parameters directory via
+sudo nano fb_defio
+change the parameter in place, and save the file.
-Accepted options:
+Unplug/replug USB device to apply with new settings
+
+Or for permanent option, create file like /etc/modprobe.d/udlfb.conf with text
+options udlfb fb_defio=0 console=1 shadow=1
+
+Accepted boolean options:
fb_defio Make use of the fb_defio (CONFIG_FB_DEFERRED_IO) kernel
module to track changed areas of the framebuffer by page faults.
- Standard fbdev applications that use mmap but that do not
- report damage, may be able to work with this enabled.
- Disabled by default because of overhead and other issues.
-
-console Allow fbcon to attach to udlfb provided framebuffers. This
- is disabled by default because fbcon will aggressively consume
- the first framebuffer it finds, which isn't usually what the
- user wants in the case of USB displays.
+ Standard fbdev applications that use mmap but that do not
+ report damage, should be able to work with this enabled.
+ Disable when running with X server that supports reporting
+ changed regions via ioctl, as this method is simpler,
+ more stable, and higher performance.
+ default: fb_defio=1
+
+console Allow fbcon to attach to udlfb provided framebuffers.
+ Can be disabled if fbcon and other clients
+ (e.g. X with --shared-vt) are in conflict.
+ default: console=1
+
+shadow Allocate a 2nd framebuffer to shadow what's currently across
+ the USB bus in device memory. If any pixels are unchanged,
+ do not transmit. Spends host memory to save USB transfers.
+ Enabled by default. Only disable on very low memory systems.
+ default: shadow=1
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