Signed-off-by: Jerry Zhang <zhangjerry@xxxxxxxxxx> --- Changes in V2: - Updated doc with the FUNCTIONFS_CONTROL_ONLY flag Documentation/usb/gadget_configfs.txt | 34 +++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/Documentation/usb/gadget_configfs.txt b/Documentation/usb/gadget_configfs.txt index 635e57493709..964edc314ee2 100644 --- a/Documentation/usb/gadget_configfs.txt +++ b/Documentation/usb/gadget_configfs.txt @@ -285,6 +285,40 @@ e.g.: $ rmdir g1 +8. Handling control requests +-------------- + +A composite gadget with changing configurations may still want to handle +vendor control requests in a centralized location. In particular, functionfs +instances can pass control requests to user-space, but there is no +guarantee that a functionfs is in the current config. + +To handle this there is a special config in the root of the gadget +called control_config. Functions linked here do not appear in the +configuration, but will receive control requests. To use it: + +Create a special instance of functionfs. + +$ mkdir functions/ffs.ctrl + +Mount the functionfs instance and write descriptors. + +mount functionfs ctrl /dev/ffs-ctrl +# Write functionfs descriptors to /dev/ffs-ctrl/ep0 +# Descriptor header must include ALL_CTRL_RECIP AND CONTROL_ONLY +# and must *not* include any speed descriptors. + +Link the function into control config. + +$ ln -s functions/ffs.ctrl control_config/f1 + +Link normal functions into the appropriate config, and enable the gadget. + +$ echo <udc name> > UDC + +Handle control requests in /dev/ffs-ctrl/ep0. +See functionfs documentation on how to do this. + -- 2.17.0.484.g0c8726318c-goog -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
