Hi,
Nokia S60 phones expose two CDC ACM channels. The first is a modem and
is properly detected by the current cdc-acm driver. The second has a
protocol ID of 0xff ('vendor specific') and /dev/ttyACM* is NOT
currently created for it.
This second channel is useful, since it's freely usable by third-party
S60 application developers. It's sometimes used for debuggers or, in our
case, remote control tools. At the S60 end, it just acts as a serial
port (as it does on Windows and MacOS X). We should expose it as
a /dev/ttyACM* device so that user-space tools can use it on Linux, too.
I attach a simple patch which does just that.
However! It's not that simple.
The reason is that some Windows Mobile/Windows CE devices support a
remote ethernet protocol called RNDIS, which is build atop CDC ACM. This
sadly uses the same class, subclass and protocol IDs.
So currently drivers/net/usb/rndis_host.c tries to register for exactly
the same devices. It eventually fails (when usbnet_generic_cdc_bind
determines that it's not a suitable ethernet interface after all). But,
if we create a serial port in cdc-acm, rndis_host doesn't even get a
chance to try.
What's the best way to allow each driver to have a crack at this
particular interface?
My plan would be:
* No longer attempt to bind to this sort of interface from
rndis_host.
* Export a function from the rndis_host driver to request for it
to try to bind to a particular interface.
* Call that function from cdc-acm, for the relevant interfaces.
* If it fails, fall back to exposing it as a tty device.
But this would introduce a dependency from cdc-acm on rndis_host, which
doesn't sound right. Can anyone suggest a better way?
Many thanks for your time,
Adrian
PS this is my first attempt at a kernel change so apologies for whatever
large parts of this e-mail are completely stupid.
Patch below:
This change causes the cdc-acm driver to create /dev/ttyACM*
files even for devices which do not claim to be modems.
This is useful, for example, with Nokia S60 devices where
the second ("vendor-specific") ACM channel is the approved
way for S60 applications to communicate with a host PC.
---
drivers/usb/class/cdc-acm.c | 11 ++++++++++-
1 files changed, 10 insertions(+), 1 deletions(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 4878528..a332104 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1390,7 +1390,16 @@ static struct usb_device_id acm_ids[] = {
{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
USB_CDC_ACM_PROTO_AT_CDMA) },
- /* NOTE: COMM/ACM/0xff is likely MSFT RNDIS ... NOT a modem!! */
+ /* vendor-specific channels. These are sometimes useful to
+ * expose as tty devices, e.g. for Nokia S60 phones where
+ * this second ACM channel can be used by phone application
+ * developers.
+ * Sadly sometimes Microsoft RNDIS interfaces also look like
+ * this; they should be claimed by the rndis_host driver. */
+ { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
+ USB_CDC_ACM_PROTO_VENDOR),
+ },
+
{ }
};
--
1.6.0.4
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