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Sebastian Andrzej Siewior
ceb3f91fd5
The status/sense URB is allocated on per-command basis. A read/write looks the following way on a stream-less connection: - send cmd tag X, queue status - receive status, oh it is a read for tag X. queue status & read - receive read - receive status, oh I'm done for tag X. Cool call complete and free status urb. This block repeats itself 1:1 for further commands and looks great so far. Lets take a look now what happens if we do allow multiple commands: - send cmd tag X, queue statusX (belongs to the command with the X tag) - send cmd tag Y, queue statusY (belongs to the command with the Y tag) - receive statusX, oh it is a read for tag X. queue statusX & a read - receive read - receive statusY, oh I'm done for tag X. Cool call complete and free statusY. - receive statusX, oh it is a read for tag Y. queue statusY & before we queue the read the the following message can be observed: |sd 0:0:0:0: [sda] sense urb submission failure followed by a second attempt with the same result. In order to address this problem we will use only one status URB for each scsi host in case we don't have stream support (as suggested by Matthew). This URB is requeued until the device removed. Nothing changes on stream based endpoints. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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.