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If isoc split in transfer with no data (the length of DATA0 packet is zero), we can't simply return immediately. Because the DATA0 can be the first transaction or the second transaction for the isoc split in transaction. If the DATA0 packet with no data is in the first transaction, we can return immediately. But if the DATA0 packet with no data is in the second transaction of isoc split in transaction sequence, we need to increase the qtd->isoc_frame_index and giveback urb to device driver if needed, otherwise, the MDATA packet will be lost. A typical test case is that connect the dwc2 controller with an usb hs Hub (GL852G-12), and plug an usb fs audio device (Plantronics headset) into the downstream port of Hub. Then use the usb mic to record, we can find noise when playback. In the case, the isoc split in transaction sequence like this: - SSPLIT IN transaction - CSPLIT IN transaction - MDATA packet (176 bytes) - CSPLIT IN transaction - DATA0 packet (0 byte) This patch use both the length of DATA0 and qtd->isoc_split_offset to check if the DATA0 is in the second transaction. Change-Id: Ie36cf25c4026f45db719c6eed036028159748b9f Signed-off-by: William Wu <william.wu@rock-chips.com> (am from https://patchwork.kernel.org/patch/10393777/)
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 ("hub_wq").
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.