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USB: gadget: storage: optional SCSI WRITE FUA bit

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MS Windows mounts removable storage in "Removal optimized mode" by
default. All the writes to the media are synchronous which is achieved
by setting FUA (Force Unit Access) bit in SCSI WRITE(10,12) commands.
This prevents I/O requests aggregation in block layer dramatically
decreasing performance.

This patch brings an option to accept or ignore mentioned bit
 a) via specifying module parameter "nofua", or
 b) through sysfs entry
	/sys/devices/platform/_UDC_/gadget/gadget-lunX/nofua
	(_UDC_ is the name of the USB Device Controller driver)

Patch is based on the work that was done by Denis Karpov for Maemo 5
platform.

Signed-off-by: Andy Shevchenko <[email protected]>
Acked-by: Alan Stern <[email protected]>
Cc: Denis Karpov <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: David Brownell <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Andy Shevchenko 2010-07-22 17:53:56 +03:00 • committed by Greg Kroah-Hartman
commit a93917d39f
3 changed files with 64 additions and 7 deletions
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12
Documentation/ABI/testing/sysfs-devices-platform-_UDC_-gadget
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@ -7,3 +7,15 @@ Description:
0 -> resumed
(_UDC_ is the name of the USB Device Controller driver)
What: /sys/devices/platform/_UDC_/gadget/gadget-lunX/nofua
Date: July 2010
Contact: Andy Shevchenko <[email protected]>
Description:
Show or set the reaction on the FUA (Force Unit Access) bit in
the SCSI WRITE(10,12) commands when a gadget in USB Mass
Storage mode.
Possible values are:
1 -> ignore the FUA flag
0 -> obey the FUA flag