USB: cxacru: add write-only sysfs attribute for modem configuration

The modem can be configured using CM_REQUEST_CARD_DATA_SET,
although CM_REQUEST_CARD_DATA_GET does not return any data.

Tested by setting the modulation (0x0a) option.

There is a list of parameters in the following archive,
but the meaning of many of them is not well documented:
  http://sourceforge.net/project/shownotes.php?release_id=301825

This source also indicates that the highest parameter set
is 0x4a but this varies by model so an arbitrary limit of
0x7f has been used (the index is a 32-bit integer).

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/networking/cxacru.txt b/Documentation/networking/cxacru.txt
index 3532ceecd2c3..f4fbf4cd592c 100644
--- a/Documentation/networking/cxacru.txt
+++ b/Documentation/networking/cxacru.txt
@@ -15,6 +15,15 @@ several sysfs attribute files for retrieving device statistics:
 * adsl_headend_environment
         Information about the remote headend.
 
+* adsl_config
+        Configuration writing interface.
+        Write parameters in hexadecimal format <index>=<value>,
+        separated by whitespace, e.g.:
+                "1=0 a=5"
+        Up to 7 parameters at a time will be sent and the modem will restart
+        the ADSL connection when any value is set. These are logged for future
+        reference.
+
 * downstream_attenuation (dB)
 * downstream_bits_per_frame
 * downstream_rate (kbps)