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