Documentation/usb/misc_ksbridge.txt

Introduction
--------------
ksbridge is a simple misc device which bridges Kickstart application
to HSIC h/w. Driver supports two instances, one instance for
flash-less-boot/ram-dumps and other instance for EFS Sync.

Initialization
--------------
Create two bridge instances and register for usb devices 0x9008 and
0x9048/0x904C. Misc device name depends on the USB PID.
For PID: 9008, misc device name is ks_bridge and for PID:9048/904C,
misc device name is efs_bridge. After KS opens the misc device, IN
URBs will be submitted to H/W; By default IN URBS are configured
to 20.

TX PATH
-------
Transmit path is very simple. Bridge driver will exposes write system
call to kickstart. Data from write call will be put into a list and a
work is scheduled to take the data from the list and write to HSIC.

Functions:
ksb_fs_write: System call invoked when kickstart writes the data
ksb_tomdm_work: Work function which submits data to HSIC h/w.

Data Structures:
to_mdm_list: Data is stored in this list
to_mdm_work: mapped to ksb_tomdm_work function

RX PATH
-------
During initialization 20 IN URBs are submitted to hsic controller. In
completion handler of each URB, buffer is de-queued and add to a list.
Read function is woken-up. A new buffer is created and submitted to
controller.

Functions:
ksb_fs_read: system call invoked by ks when it tries to read the data
ksb_rx_cb: rx urb completion handler
ksb_start_rx_work: function called during initialization.

Data Structures:
ks_wait_q: read system call will block on this queue until data is
available or device is disconnected
to_ks_list: data queued to this list by rx urb completion handler,
later de-queued by read system call.