kernel_optimize_test/drivers/usb
Sarah Sharp 51e0a01206 USB: Calculate USB 3.0 exit latencies for LPM.
There are several different exit latencies associated with coming out of
the U1 or U2 lower power link state.

Device Exit Latency (DEL) is the maximum time it takes for the USB
device to bring its upstream link into U0.  That can be found in the
SuperSpeed Extended Capabilities BOS descriptor for the device.  The
time it takes for a particular link in the tree to exit to U0 is the
maximum of either the parent hub's U1/U2 DEL, or the child's U1/U2 DEL.

Hubs introduce a further delay that effects how long it takes a child
device to transition to U0.  When a USB 3.0 hub receives a header
packet, it takes some time to decode that header and figure out which
downstream port the packet was destined for.  If the port is not in U0,
this hub header decode latency will cause an additional delay for
bringing the child device to U0.  This Hub Header Decode Latency is
found in the USB 3.0 hub descriptor.

We can use DEL and the header decode latency, along with additional
latencies imposed by each additional hub tier, to figure out the exit
latencies for both host-initiated and device-initiated exit to U0.

The Max Exit Latency (MEL) is the worst-case time it will take for a
host-initiated exit to U0, based on whether U1 or U2 link states are
enabled.  The ping or packet must traverse the path to the device, and
each hub along the way incurs the hub header decode latency in order to
figure out which device the transfer was bound for.  We say worst-case,
because some hubs may not be in the lowest link state that is enabled.
See the examples in section C.2.2.1.

Note that "HSD" is a "host specific delay" that the power appendix
architect has not been able to tell me how to calculate.  There's no way
to get HSD from the xHCI registers either, so I'm simply ignoring it.

The Path Exit Latency (PEL) is the worst-case time it will take for a
device-initiate exit to U0 to place all the links from the device to the
host into U0.

The System Exit Latency (SEL) is another device-initiated exit latency.
SEL is useful for USB 3.0 devices that need to send data to the host at
specific intervals.  The device may send an NRDY to indicate it isn't
ready to send data, then put its link into a lower power state.  If it
needs to have that data transmitted at a specific time, it can use SEL
to back calculate when it will need to bring the link back into U0 to
meet its deadlines.

SEL is the worst-case time from the device-initiated exit to U0, to when
the device will receive a packet from the host controller.  It includes
PEL, the time it takes for an ERDY to get to the host, a host-specific
delay for the host to process that ERDY, and the time it takes for the
packet to traverse the path to the device.  See Figure C-2 in the USB
3.0 bus specification.

Note: I have not been able to get good answers about what the
host-specific delay to process the ERDY should be.  The Intel HW
developers say it will be specific to the platform the xHCI host is
integrated into, and they say it's negligible.  Ignore this too.

Separate from these four exit latencies are the U1/U2 timeout values we
program into the parent hubs.  These timeouts tell the hub to attempt to
place the device into a lower power link state after the link has been
idle for that amount of time.

Create two arrays (one for U1 and one for U2) to store mel, pel, sel,
and the timeout values.  Store the exit latency values in nanosecond
units, since that's the smallest units used (DEL is in us, but the Hub
Header Decode Latency is in ns).

If a USB 3.0 device doesn't have a SuperSpeed Extended Capabilities BOS
descriptor, it's highly unlikely it will be able to handle LPM requests
properly.  So it's best to disable LPM for devices that don't have this
descriptor, and any children beneath it, if it's a USB 3.0 hub.  Warn
users when that happens, since it means they have a non-compliant USB
3.0 device or hub.

This patch assumes a simplified design where links deep in the tree will
not have U1 or U2 enabled unless all their parent links have the
corresponding LPM state enabled.  Eventually, we might want to allow a
different policy, and we can revisit this patch when that happens.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
2012-05-18 15:41:56 -07:00
..
atm USB: xusbatm.c: remove dbg() usage 2012-05-01 21:33:30 -07:00
c67x00
chipidea usb: chipidea: remove zero check of hw_ep_max 2012-05-15 08:43:40 -07:00
class USB: cdc-wdm: remove from device list on disconnect 2012-05-11 15:19:22 -07:00
core USB: Calculate USB 3.0 exit latencies for LPM. 2012-05-18 15:41:56 -07:00
dwc3 usb: dwc3: Fix the dwc3 dependency 2012-05-11 15:17:31 -07:00
early
gadget usb: gadget: at91_udc: fix endpoint descriptor dereference 2012-05-16 05:29:20 -07:00
host xhci: Add roothub code to set U1/U2 timeouts. 2012-05-18 15:41:52 -07:00
image USB: mdc800.c: remove dbg() usage 2012-05-01 21:33:50 -07:00
misc USB: yurex.c: remove dbg() usage 2012-05-01 21:34:11 -07:00
mon
musb usb: musb: cppi: add missing include to fix compilation 2012-05-14 12:45:45 -07:00
otg USB: gpio_vbus: avoid consecutive vbus_session calls with the same "is_active" 2012-05-14 09:02:23 -07:00
phy USB: Add driver for NXP ISP1301 USB transceiver 2012-05-01 13:33:02 -04:00
renesas_usbhs usb: renesas_usbhs: gadget: add support for set_selfpowered 2012-05-04 15:53:05 +03:00
serial Revert "USB: serial: sierra: put reset_resume callback back." 2012-05-16 08:39:56 -07:00
storage USB: storage: fixed keyword related space issues. 2012-05-17 09:48:29 -07:00
wusbcore
Kconfig usb: move ci13xxx and related code to drivers/usb/chipidea 2012-05-11 16:45:30 -07:00
Makefile usb: move ci13xxx and related code to drivers/usb/chipidea 2012-05-11 16:45:30 -07:00
README
usb-common.c
usb-skeleton.c USB: usb-skeleton.c: remove err() usage 2012-04-27 11:24:45 -07:00

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.