[U-Boot] [PATCH v4 0/4] usb: Reduce USB scanning time

[Stefan Roese]

My current x86 platform (Bay Trail, not in mainline yet) has a quite
complex USB infrastructure with many USB hubs. Here the USB scan takes
an incredible huge amount of time:

starting USB...
USB0:   USB EHCI 1.00
scanning bus 0 for devices... 9 USB Device(s) found

time: 28.415 seconds

This is of course not acceptable on platforms, where USB needs to get
scanned at every bootup. As this increases the bootup time of this
device by nearly 30 seconds!

This patch series greatly reduces the USB scanning time. This is done
by multiple means:

- Remove or reduce delays and timeouts
- Remove a 2nd reset of the USB hubs
- Change USB port timeout handling and introduce quasi parallel USB
  port scanning

As a result, the USB scanning time is greatly reduced:

starting USB...
USB0:   USB EHCI 1.00
scanning bus 0 for devices... 9 USB Device(s) found

time: 1.822 seconds

As you can see, the time is reduced from 28.4 to 1.8 seconds!

Please find more details to the changes in the patch description.

Testing and comments welcome!

Thanks,
Stefan

Changes in v4:
- Minor rewording / fixes of the commit text
- Add Acked-by / Tested-by from Hans and Stephen
- Minor rewording / fixes of the commit text
- Add Acked-by from Hans
- Moved check for query_delay into usb_scan_port() as suggested by Hans
- Correct list handling (drop INIT_LIST_HEAD)
- Added some missing free() calls
- Changed connect_timeout calculation as suggested by Stephen
- Moved usb_scan_list to other globals to be cleaned up in a later patch
- Added timeout check for non-functional ports (usb_get_port_status
  return error
- Reverted if logic in loop to remove an indentation level
- Moved debug() output
- Removed unnecessary if when already connected
- Added Hans's Acked-by
- Added Stephen's Tested-by
- Minor rewording / fixes of the commit text

Changes in v3:
- Changed small timeout from 10ms to 20ms as this results in a
  much faster USB scanning time (10ms too small and 20ms enough
  in many cases)
- Introduced scanning list containing all USB devices of one USB
  controller that need to get scanned
- Don't delay in usb_hub_power_on(). Instead skip querying these devices
  until the delay time is reached.

Changes in v2:
- Add Acked-by / Tested-by from Hans and Stephen
- Make this change unconditional
- Add Acked-by / Tested-by from Hans and Stephen
- Make this change unconditional
- Add Tested-by from Stephen
- Remove static USB port configuration patch (for now)

Stefan Roese (4):
  usb: legacy_hub_port_reset(): Speedup hub reset handling
  usb: Remove 200 ms delay in usb_hub_port_connect_change()
  usb: Don't reset the USB hub a 2nd time
  usb: Change power-on / scanning timeout handling

 common/usb.c     |  13 +--
 common/usb_hub.c | 305 +++++++++++++++++++++++++++++++++++++------------------
 include/usb.h    |   3 +
 3 files changed, 212 insertions(+), 109 deletions(-)

-- 
2.7.3