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udlfb: Add module option to do without shadow framebuffer

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By default, udlfb allocates a 2nd buffer to shadow what's across
the bus on the USB device.  It can operate without this shadow,
but then it cannot tell which pixels have changed, and must send all.

Saves host memory, but worsens the USB 2.0 bus bottleneck.

This option allows users in very low memory situations (e.g.
bifferboard) to optionally turn off this shadow framebuffer.

Signed-off-by: Stuart Hopkins <stuart@linux-depot.com>
Signed-off-by: Bernie Thompson <bernie@plugable.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
This commit is contained in:
Stuart Hopkins
2011-08-21 13:34:17 -07:00
committed by Florian Tobias Schandinat
parent def7660868
commit d3189545ee
2 changed files with 13 additions and 2 deletions
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Documentation/fb/udlfb.txt
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@@ -105,6 +105,11 @@ console Allow fbcon to attach to udlfb provided framebuffers. This
the first framebuffer it finds, which isn't usually what the
user wants in the case of USB displays.
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.
Sysfs Attributes
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