usb: gadget: mass_storage: add documentation

This commit adds Documentation/usb/mass-storage.txt file.  It contains
description of how to use the mass storage gadget from user space.  It
elaborates on madule parameters and sysfs interface more then it was
written in the comments in the source code.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 7 insertions, 62 deletions

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 9b29e8eab18..7ad4f819752 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -44,12 +44,12 @@
  * function for a USB device, it also illustrates a technique of
  * double-buffering for increased throughput.
  *
- * Function supports multiple logical units (LUNs).  Backing storage
- * for each LUN is provided by a regular file or a block device.
- * Access for each LUN can be limited to read-only.  Moreover, the
- * function can indicate that LUN is removable and/or CD-ROM.  (The
- * later implies read-only access.)
- *
+ * For more information about MSF and in particular its module
+ * parameters and sysfs interface read the
+ * <Documentation/usb/mass-storage.txt> file.
+ */
+
+/*
  * MSF is configured by specifying a fsg_config structure.  It has the
  * following fields:
  *
@@ -95,61 +95,6 @@
  * data track and no audio tracks; hence there need be only one
  * backing file per LUN.
  *
- *
- * MSF includes support for module parameters.  If gadget using it
- * decides to use it, the following module parameters will be
- * available:
- *
- *	file=filename[,filename...]
- *			Names of the files or block devices used for
- *				backing storage.
- *	ro=b[,b...]	Default false, boolean for read-only access.
- *	removable=b[,b...]
- *			Default false, boolean for removable media.
- *	cdrom=b[,b...]	Default false, boolean for whether to emulate
- *				a CD-ROM drive.
- *	nofua=b[,b...]	Default false, booleans for ignore FUA flag
- *				in SCSI WRITE(10,12) commands
- *	luns=N		Default N = number of filenames, number of
- *				LUNs to support.
- *	stall		Default determined according to the type of
- *				USB device controller (usually true),
- *				boolean to permit the driver to halt
- *				bulk endpoints.
- *
- * The module parameters may be prefixed with some string.  You need
- * to consult gadget's documentation or source to verify whether it is
- * using those module parameters and if it does what are the prefixes
- * (look for FSG_MODULE_PARAMETERS() macro usage, what's inside it is
- * the prefix).
- *
- *
- * Requirements are modest; only a bulk-in and a bulk-out endpoint are
- * needed.  The memory requirement amounts to two 16K buffers, size
- * configurable by a parameter.  Support is included for both
- * full-speed and high-speed operation.
- *
- * Note that the driver is slightly non-portable in that it assumes a
- * single memory/DMA buffer will be useable for bulk-in, bulk-out, and
- * interrupt-in endpoints.  With most device controllers this isn't an
- * issue, but there may be some with hardware restrictions that prevent
- * a buffer from being used by more than one endpoint.
- *
- *
- * The pathnames of the backing files, the ro settings and nofua
- * settings are available in the attribute files "file", "ro" and
- * "nofua" in the lun<n> subdirectory of the gadget's sysfs directory.
- * If the "removable" option is set, writing to these files will
- * simulate ejecting/loading the medium (writing an empty line means
- * eject) and adjusting a write-enable tab.  Changes to the ro setting
- * are not allowed when the medium is loaded or if CD-ROM emulation is
- * being used.
- *
- * When a LUN receive an "eject" SCSI request (Start/Stop Unit),
- * if the LUN is removable, the backing file is released to simulate
- * ejection.
- *
- *
  * This function is heavily based on "File-backed Storage Gadget" by
  * Alan Stern which in turn is heavily based on "Gadget Zero" by David
  * Brownell.  The driver's SCSI command interface was based on the
@@ -191,7 +136,7 @@
  * In normal operation the main thread is started during the gadget's
  * fsg_bind() callback and stopped during fsg_unbind().  But it can
  * also exit when it receives a signal, and there's no point leaving
- * the gadget running when the thread is dead.  At of this moment, MSF
+ * the gadget running when the thread is dead.  As of this moment, MSF
  * provides no way to deregister the gadget when thread dies -- maybe
  * a callback functions is needed.
  *