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diff --git a/Documentation/ABI/testing/sysfs-platform-at91 b/Documentation/ABI/testing/sysfs-platform-at91
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index 000000000000..4cc6a865ae66
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+++ b/Documentation/ABI/testing/sysfs-platform-at91
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+What:           /sys/devices/platform/at91_can/net/<iface>/mb0_id
+Date:           January 2011
+KernelVersion:  2.6.38
+Contact:        Marc Kleine-Budde <kernel@pengutronix.de>
+Description:
+                Value representing the can_id of mailbox 0.
+
+                Default: 0x7ff (standard frame)
+
+                Due to a chip bug (errata 50.2.6.3 & 50.3.5.3 in
+                "AT91SAM9263 Preliminary 6249H-ATARM-27-Jul-09") the
+                contents of mailbox 0 may be send under certain
+                conditions (even if disabled or in rx mode).
+
+                The workaround in the errata suggests not to use the
+                mailbox and load it with an unused identifier.
+
+                In order to use an extended can_id add the
+                CAN_EFF_FLAG (0x80000000U) to the can_id. Example:
+
+                - standard id 0x7ff:
+                echo 0x7ff      > /sys/class/net/can0/mb0_id
+
+                - extended id 0x1fffffff:
+                echo 0x9fffffff > /sys/class/net/can0/mb0_id