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Diffstat (limited to 'Documentation/usb/raw-gadget.rst')
| -rw-r--r-- | Documentation/usb/raw-gadget.rst | 37 |
1 files changed, 30 insertions, 7 deletions
diff --git a/Documentation/usb/raw-gadget.rst b/Documentation/usb/raw-gadget.rst index 9e78cb858f86..68d879a8009e 100644 --- a/Documentation/usb/raw-gadget.rst +++ b/Documentation/usb/raw-gadget.rst @@ -27,9 +27,8 @@ differences are: 3. Raw Gadget provides a way to select a UDC device/driver to bind to, while GadgetFS currently binds to the first available UDC. -4. Raw Gadget uses predictable endpoint names (handles) across different - UDCs (as long as UDCs have enough endpoints of each required transfer - type). +4. Raw Gadget explicitly exposes information about endpoints addresses and + capabilities allowing a user to write UDC-agnostic gadgets. 5. Raw Gadget has ioctl-based interface instead of a filesystem-based one. @@ -50,12 +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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- Implement ioctl's for setting/clearing halt status on endpoints. - -- 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). |