[3/3] Documentation: usb: Add docs for configfs control requests

Commit Message

Jerry Zhang July 2, 2018, 10:01 p.m. UTC

Signed-off-by: Jerry Zhang <[e-mail]>
---
 Documentation/usb/gadget_configfs.txt | 34 +++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

Comments

Greg Kroah-Hartman July 3, 2018, 6:35 a.m. UTC | #1

On Mon, Jul 02, 2018 at 03:01:03PM -0700, Jerry Zhang wrote:
> Signed-off-by: Jerry Zhang <[e-mail]>
> ---
>  Documentation/usb/gadget_configfs.txt | 34 +++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)

I can't take patches without any changelog text at all, sorry.

greg k-h
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Patch

diff --git a/Documentation/usb/gadget_configfs.txt b/Documentation/usb/gadget_configfs.txt
index b8cb38a98c19..64f69dd3f123 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.
+