mirror of https://gitee.com/openkylin/linux.git
79abb1ab13
Originally, the USB core had no support for allocating bandwidth when a particular configuration or alternate setting for an interface was selected. Instead, the device driver's URB submission would fail if there was not enough bandwidth for a periodic endpoint. Drivers could work around this, by using the scatter-gather list API to guarantee bandwidth. This patch adds host controller API to allow the USB core to allocate or deallocate bandwidth for an endpoint. Endpoints are added to or dropped from a copy of the current schedule by calling add_endpoint() or drop_endpoint(), and then the schedule is atomically evaluated with a call to check_bandwidth(). This allows all the endpoints for a new configuration or alternate setting to be added at the same time that the endpoints from the old configuration or alt setting are dropped. Endpoints must be added to the schedule before any URBs are submitted to them. The HCD must be allowed to reject a new configuration or alt setting before the control transfer is sent to the device requesting the change. It may reject the change because there is not enough bandwidth, not enough internal resources (such as memory on an embedded host controller), or perhaps even for security reasons in a virtualized environment. If the call to check_bandwidth() fails, the USB core must call reset_bandwidth(). This causes the schedule to be reverted back to the state it was in just after the last successful check_bandwidth() call. If the call succeeds, the host controller driver (and hardware) will have changed its internal state to match the new configuration or alternate setting. The USB core can then issue a control transfer to the device to change the configuration or alt setting. This allows the core to test new configurations or alternate settings before unbinding drivers bound to interfaces in the old configuration. WIP: The USB core must add endpoints from all interfaces in a configuration to the schedule, because a driver may claim that interface at any time. A slight optimization might be to add the endpoints to the schedule once a driver claims that interface. FIXME This patch does not cover changing alternate settings, but it does handle a configuration change or de-configuration. FIXME The code for managing the schedule is currently HCD specific. A generic scheduling algorithm could be added for host controllers without built-in scheduling support. For now, if a host controller does not define the check_bandwidth() function, the call to usb_hcd_check_bandwidth() will always succeed. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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| class | ||
| core | ||
| gadget | ||
| host | ||
| image | ||
| misc | ||
| mon | ||
| musb | ||
| otg | ||
| serial | ||
| storage | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-skeleton.c | ||
README
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.