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This patch adds the support in UVC webcam gadget design for providing USB_GADGET_DELAYED_STATUS in response to a set_interface(alt setting 1) command issue by the Host. The current UVC webcam gadget design generates a STREAMON event corresponding to a set_interface(alt setting 1) command from the Host. This STREAMON event will eventually be routed to a real V4L2 device. To start video streaming, it may be required to perform some register writes to a camera sensor device over slow external busses like I2C or SPI. So, it makes sense to ensure that we delay the STATUS stage of the set_interface (alt setting 1) command. Otherwise, a lot of ISOC IN tokens sent by the Host will be replied to by zero-length packets by the webcam device. On certain Hosts this may even lead to ISOC URBs been cancelled from the Host side. So, as soon as we finish doing all the "streaming" related stuff on the real V4L2 device, we call a STREAMON ioctl on the UVC side and from here we call the 'usb_composite_setup_continue' function to complete the status stage of the set_interface(alt setting 1) command. Further, we need to ensure that we queue no video buffers on the UVC webcam gadget, until we de-queue a video buffer from the V4L2 device. So, the application should call the STREAMON on UVC side only when it has dequeued sufficient buffers from the V4L2 side and queued them to the UVC gadget. Signed-off-by: Bhupesh Sharma <bhupesh.sharma@st.com> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Tested-by: Bhupesh Sharma <bhupesh.sharma@st.com> Signed-off-by: Felipe Balbi <balbi@ti.com>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("khubd").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.