9238f25d5d
For periodic endpoints, we must let the xHCI hardware know the maximum payload an endpoint can transfer in one service interval. The xHCI specification refers to this as the Maximum Endpoint Service Interval Time Payload (Max ESIT Payload). This is used by the hardware for bandwidth management and scheduling of packets. For SuperSpeed endpoints, the maximum is calculated by multiplying the max packet size by the number of bursts and the number of opportunities to transfer within a service interval (the Mult field of the SuperSpeed Endpoint companion descriptor). Devices advertise this in the wBytesPerInterval field of their SuperSpeed Endpoint Companion Descriptor. For high speed devices, this is taken by multiplying the max packet size by the "number of additional transaction opportunities per microframe" (the high bits of the wMaxPacketSize field in the endpoint descriptor). For FS/LS devices, this is just the max packet size. The other thing we must set in the endpoint context is the Average TRB Length. This is supposed to be the average of the total bytes in the transfer descriptor (TD), divided by the number of transfer request blocks (TRBs) it takes to describe the TD. This gives the host controller an indication of whether the driver will be enqueuing a scatter gather list with many entries comprised of small buffers, or one contiguous buffer. It also takes into account the number of extra TRBs you need for every TD. This includes No-op TRBs and Link TRBs used to link ring segments together. Some drivers may choose to chain an Event Data TRB on the end of every TD, thus increasing the average number of TRBs per TD. The Linux xHCI driver does not use Event Data TRBs. In theory, if there was an API to allow drivers to state what their bandwidth requirements are, we could set this field accurately. For now, we set it to the same number as the Max ESIT payload. The Average TRB Length should also be set for bulk and control endpoints, but I have no idea how to guess what it should be. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
||
|---|---|---|
| .. | ||
| atm | ||
| c67x00 | ||
| class | ||
| core | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| misc | ||
| mon | ||
| musb | ||
| otg | ||
| serial | ||
| storage | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-skeleton.c | ||
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.