SM501: Add Documentation/SM501.txt

			SM501 Driver

			============

Copyright 2006, 2007 Simtec Electronics

Core

----

The core driver in drivers/mfd provides common services for the

drivers which manage the specific hardware blocks. These services

include locking for common registers, clock control and resource

management.

The core registers drivers for both PCI and generic bus based

chips via the platform device and driver system.

On detection of a device, the core initialises the chip (which may

be specified by the platform data) and then exports the selected

peripheral set as platform devices for the specific drivers.

The core re-uses the platform device system as the platform device

system provides enough features to support the drivers without the

need to create a new bus-type and the associated code to go with it.

Resources

---------

Each peripheral has a view of the device which is implicitly narrowed to

the specific set of resources that peripheral requires in order to

function correctly.

The centralised memory allocation allows the driver to ensure that the

maximum possible resource allocation can be made to the video subsystem

as this is by-far the most resource-sensitive of the on-chip functions.

The primary issue with memory allocation is that of moving the video

buffers once a display mode is chosen. Indeed when a video mode change

occurs the memory footprint of the video subsystem changes.

Since video memory is difficult to move without changing the display

(unless sufficient contiguous memory can be provided for the old and new

modes simultaneously) the video driver fully utilises the memory area

given to it by aligning fb0 to the start of the area and fb1 to the end

of it. Any memory left over in the middle is used for the acceleration

functions, which are transient and thus their location is less critical

as it can be moved.

Configuration

-------------

The platform device driver uses a set of platform data to pass

configurations through to the core and the subsidiary drivers

so that there can be support for more than one system carrying

an SM501 built into a single kernel image.

The PCI driver assumes that the PCI card behaves as per the Silicon

Motion reference design.

There is an errata (AB-5) affecting the selection of the

of the M1XCLK and M1CLK frequencies. These two clocks

must be sourced from the same PLL, although they can then

be divided down individually. If this is not set, then SM501 may

lock and hang the whole system. The driver will refuse to

attach if the PLL selection is different.