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-rw-r--r--Documentation/ABI/testing/sysfs-module23
1 files changed, 23 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module
index cfcec3bffc0a..9489ea8e294c 100644
--- a/Documentation/ABI/testing/sysfs-module
+++ b/Documentation/ABI/testing/sysfs-module
@@ -10,3 +10,26 @@ KernelVersion: 2.6.35
Contact: masa-korg@dsn.okisemi.com
Description: Write/read Option ROM data.
+
+What: /sys/module/ehci_hcd/drivers/.../uframe_periodic_max
+Date: July 2011
+KernelVersion: 3.1
+Contact: Kirill Smelkov <kirr@mns.spb.ru>
+Description: Maximum time allowed for periodic transfers per microframe (μs)
+
+ [ USB 2.0 sets maximum allowed time for periodic transfers per
+ microframe to be 80%, that is 100 microseconds out of 125
+ microseconds (full microframe).
+
+ However there are cases, when 80% max isochronous bandwidth is
+ too limiting. For example two video streams could require 110
+ microseconds of isochronous bandwidth per microframe to work
+ together. ]
+
+ Through this setting it is possible to raise the limit so that
+ the host controller would allow allocating more than 100
+ microseconds of periodic bandwidth per microframe.
+
+ Beware, non-standard modes are usually not thoroughly tested by
+ hardware designers, and the hardware can malfunction when this
+ setting differ from default 100.