HID: add framebuffer support to PicoLCD device

Add framebuffer support to PicoLCD device with use of deferred-io.

Only changed areas of framebuffer get sent to device in order to
save USB bandwidth and especially resources on PicoLCD device or
allow higher refresh rate for a small area. Changed tiles are
determined while updating shadow framebuffer.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-hid-picolcd b/Documentation/ABI/testing/sysfs-driver-hid-picolcd
index 6fb4f21469f7..14f52d70621b 100644
--- a/Documentation/ABI/testing/sysfs-driver-hid-picolcd
+++ b/Documentation/ABI/testing/sysfs-driver-hid-picolcd
@@ -15,3 +15,20 @@ Description:	Make it possible to switch the PicoLCD device between LCD
                 disconnected and reconnects after above delay (default value
                 is 5 seconds though this default should not be relied on).
 
+
+What:           /sys/bus/usb/devices/<busnum>-<devnum>:<config num>.<interface num>/<hid-bus>:<vendor-id>:<product-id>.<num>/fb_update_rate
+Date:           March 2010
+Contact:        Bruno Prémont <bonbons@linux-vserver.org>
+Description:    Make it possible to adjust defio refresh rate.
+
+                Reading: returns list of available refresh rates (expressed in Hz),
+                the active refresh rate being enclosed in brackets ('[' and ']')
+
+                Writing: accepts new refresh rate expressed in integer Hz
+                within permitted rates.
+
+                Note: As device can barely do 2 complete refreshes a second
+                it only makes sense to adjust this value if only one or two
+                tiles get changed and it's not appropriate to expect the application
+                to flush it's tiny changes explicitely at higher than default rate.
+