The protocol is implemented using control requests. The display is implemented as a vendor type USB interface with one bulk out endpoint. It presents a DRM display device as a USB Display configured through configfs. This adds the gadget side support for the Generic USB Display. The driver is MIT licensed to smooth the path for any BSD port of the driver. It is added in preparation for future monochrome e-ink displays. This is not implemented in the gadget driver. The driver supports a one bit monochrome transfer format: R1. LZ4 compression is used if the device supports it. Optimal user experience is achieved by providing damage reports either by setting FB_DAMAGE_CLIPS on pageflips or calling DRM_IOCTL_MODE_DIRTYFB. If the device transfer buffer can't fit an uncompressed framebuffer update, the update is split up into parts that do fit. Performance is preferred over color depth, so if the device supports RGB565, DRM_CAP_DUMB_PREFERRED_DEPTH will return 16. If both are present, EDID is just passed on to userspace. There is also support for backlight brightness exposed as a backlight device.ĭisplay modes can be made available to the host driver either as DRM display modes or through EDID. The following DRM properties are supported: The Linux gadget device driver will serve as the canonical device implementation. This adds a generic USB display driver with the intention that it can be used with future USB interfaced low end displays/adapters. The generic USB display driver patch explains all the interesting technical details: A video embedded below shows the Generic USB display driver in action with different hosts/devices. Performance is obviously a big concern for USB-based displays but even for low-end Raspberry Pi hardware he's been getting some promising results. It would have been nice to have a microcontroller implementation to ensure that I haven't made things unnecessary difficult to implement.' I was hoping to have someone working on a microcontroller based USB display by now, but unfortunately that has been delayed. Noralf noted, ' The reason for calling it 'Generic' is so anyone can make a USB display/adapter against this driver, all that's needed is to add a USB vid:pid. The Generic USB Display Driver is a generic solution for using the likes of the Raspberry Pi SBCs into converting them into makeshift USB display adapters via a new USB host driver and a device/gadget driver.

This driver was written following his idea of turning a Raspberry Pi Zero into a USB to HDMI display adapter. Longtime Linux DRM developer Noralf Trønnes has written a new driver for Linux to serve generic USB display purposes.

Generic usb audio driver linux