The driver is also requested to unbind and clean up any device state, before this procedure finally returns. Other steps are handled by the gadget driver. It provides two configurations: The API standardizes a platform-neutral boundary between two software layers, but the software stack usually has several higher layers. Devices which rely on bus powered operation should report this in their bind method.

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An example of multiple activations might be a CDC ACM function that supports two or more distinct instances within the same configuration, providing several independent logical data links to a USB host.

It provides two configurations: Recent kernels substantially simplify the work involved in supporting new hardware, by autoconfiguring endpoints automatically for many gaddgetfs drivers.

It a good base for integrating and re-using this type of driver code. Such issues are in the domain of gadget drivers, including knowing about implementation gadgetf imposed by some USB controllers or understanding that composite devices might happen to be built by integrating reusable components. The API supports limited run-time detection of capabilities, through naming conventions for endpoints.

It’s all but a rewrite, and supports high speed host-only, peripheral-only, and OTG modes.

These provide a software “gadget” device, visible in sysfs. You should assign those addresses using a registered IEEE company id ; this will also make the gadgetts appear to Linux hosts as an “ethN” interface, not as “usbN”. Except for the driver data, all fields in this structure are read-only to the gadget driver. Adding a function involves calling its bind method to allocate resources such as interface and string identifiers and endpoints.


These are the same types and constants used by host side drivers and usbcore. The core API is sufficient for writing gargetfs for composite USB devices with more than one function in a given configurationand also multi-configuration devices also more than one function, but not necessarily sharing a given configuration. These aren’t a separate library or midlayer, they’re just object files optionally linked with gaddgetfs drivers that want their functions.

Register a gadget driver linuxx implements some higher level device function. Convenience functions make it easier to test which of the currently configured controller chips is being used.

This function chooses the right descriptors for a given endpoint according to gadget speed and saves it in the endpoint desc field. Other recent updates have included support for “soft connect”, where the gadget driver controls the pullup used in enumeration; declaring allowable power consumption, helping control things like battery recharge rates; supporting external transceiver that sense VBUS sessions; and peripheral-side OTG features.

Endpoint autoconfiguration hides some hardware-specific initialization issues from gadget drivers, such as endpoint addressing; simple gadget drivers may no longer need hardware-specific logic. Linux users with embedded systems are more likely to have USB peripheral hardware.

USB/Linux USB Layers/GadgetFs

Unless otherwise noted, these are full speed controllers. More information about OTG on Linux is available.

When the gadget driver module is being unloaded, the driver unbind callback is issued. Mentor Graphics supplies a preliminary GPL’d high speed stackbuilding on the gadget API and used with chips integrating their silicon design.


USB/Linux USB Layers/GadgetFs – Tizen Wiki

Most new development is based on 2. Those issues may be handled at various points: Because such hardware varies widely in capabilities gaddgetfs restrictions, and is used lunux embedded environments where space is at gadgetds premium, the gadetfs driver is often configured at compile time to work with endpoints supported by one particular controller. On most hardware, several different layers can be fed by the gadget driver at the same time. One interesting use of that driver is in boot firmware like a BIOSwhich can sometimes use that model with very small systems without real serial lines.

On disconnect, the drivers go back to step 3 above. For example, the functions on a composite device might give hosts concurrent access to local audio, internet, and file servers. There are significant hardware features, such as device-to-device DMA without temporary storage in a memory buffer that would be added using hardware-specific APIs. Not all controllers support isochronous transfers, as needed for audio and video class drivers.

Gadget drivers may be portable to several different controllers, using conditional compilation. SRP support can be user-initiated just like remote wakeup, probably by pressing the same button.