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usb: raw-gadget: documentation updates 

Mention the issue with fixed UDC addresses.

Links external examples and test suite.

Add more implmenetation details and potential improvements.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
alistair/sunxi64-5.7-dsi
Andrey Konovalov 2020-05-07 19:06:58 +02:00 committed by Felipe Balbi
parent c61769bd47
commit 61d2658db4
1 changed files with 28 additions and 2 deletions
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30
Documentation/usb/raw-gadget.rst
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@ -49,10 +49,36 @@ The typical usage of Raw Gadget looks like:
Raw Gadget and react to those depending on what kind of USB device
needs to be emulated.
Note, that some UDC drivers have fixed addresses assigned to endpoints, and
therefore arbitrary endpoint addresses can't be used in the descriptors.
Nevertheles, Raw Gadget provides a UDC-agnostic way to write USB gadgets.
Once a USB_RAW_EVENT_CONNECT event is received via USB_RAW_IOCTL_EVENT_FETCH,
the USB_RAW_IOCTL_EPS_INFO ioctl can be used to find out information about
endpoints that the UDC driver has. Based on that information, the user must
chose UDC endpoints that will be used for the gadget being emulated, and
properly assign addresses in endpoint descriptors.
You can find usage examples (along with a test suite) here:
https://github.com/xairy/raw-gadget
Internal details
~~~~~~~~~~~~~~~~
Currently every endpoint read/write ioctl submits a USB request and waits until
its completion. This is the desired mode for coverage-guided fuzzing (as we'd
like all USB request processing happen during the lifetime of a syscall),
and must be kept in the implementation. (This might be slow for real world
applications, thus the O_NONBLOCK improvement suggestion below.)
Potential future improvements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Reporting more events (suspend, resume, etc.) through
USB_RAW_IOCTL_EVENT_FETCH.
- Report more events (suspend, resume, etc.) through USB_RAW_IOCTL_EVENT_FETCH.
- Support O_NONBLOCK I/O.
- Support USB 3 features (accept SS endpoint companion descriptor when
enabling endpoints; allow providing stream_id for bulk transfers).
- Support ISO transfer features (expose frame_number for completed requests).