kernel_samsung_msm8974/Documentation/arm/msm/msm_sharedmem.txt

Introduction
============

This is a new platform driver for newly introduced UIO devices
to facilitate clients in Userspace.

Hardware description
====================
This driver does not implement any specific hardware driver.

Software description
====================

Design
======

The goal of this driver is to ensure there is no security lapse in the
Userspace clients' functionality. This new driver uses the existing
UIO framework to facilitate the clients to be able to memory map their
respective allotted shared memory address in the client's address space.

				  |
    Userspace			  |		Kernel space
 +--------------+	+---------------+	+---------------+
 |   Client	|	|  Shared	|	|  shrdmem_uio	|
 |		<------->    Memory	<------->  driver	|
 +--------------+	+---------------+	+---------------+
				  |
				  |

The shared memory (a transport buffer) address is unique for each
individual client and is made available to the driver via device tree.

For a given client the probe would be called once in the shrdmem_uio driver.
This driver would parse the device tree and register a new UIO device with kernel
available under /dev/uioX (where X would start from zero, being serially
incremented for the next UIO device probed)

The client in Userspace would be able to access the respective UIO device
under the sysfs entry(/sys/class/uio/uioX) upon verifying the name and version
of the device under this sysfs node. Once verified it could access the physical
address under /sys/class/uio/uioX/maps/map0/addr

The client would request for memory mapping which would be taken care of in the
kernel space by the UIO framework. No explicit mmap() implementation required by
the shrdmem_uio driver.

Power Management
================
Does not implement any power management.

SMP/multi-core
==============

The platform driver would be loaded/probed once per client.
DTS files will be looked up for shared memory addresses and sizes for all the clients.
The UIO char device will be created under /dev/uioX.

This being one time activity for a given client it does not require SMP/multi-core safety.

Security
========

The devices (/dev/uioX) would have permission checks for restricted access

Performance
===========

None.

Interface
=========

This driver does not export any APIs for kernel.
Android user space can access the shared memory by mmaping it.

Driver parameters
=================

None.

Config options
==============

None.

Dependencies
============

The only dependency is the kernel device tree files for the
Userspace client details.

User space utilities
====================
This driver communicates with the following user space clients/utilities:

Remote File System:
 - Based on Qualcomm Messaging Interface (QMI)
 - This service enables the modules on the MSM modem processor to
   read data from and write data to the embedded multimedia card (eMMC),
   which is solely controlled by the applications processor.

Remote File System Access (QMI_RFSA):
 - Based on Qualcomm Messaging Interface (QMI)
 - This service provides access from the Hexagon processor to a High-Level
   Operating Sytem (HLOS) file system
Other
=====

None.

Known issues
============

None.