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Documentation / SM501.txt

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Based on kernel version 4.9. Page generated on 2016-12-21 14:37 EST.

1				SM501 Driver
2				============
4	Copyright 2006, 2007 Simtec Electronics
6	The Silicon Motion SM501 multimedia companion chip is a multifunction device
7	which may provide numerous interfaces including USB host controller USB gadget,
8	asynchronous serial ports, audio functions, and a dual display video interface.
9	The device may be connected by PCI or local bus with varying functions enabled.
11	Core
12	----
14	The core driver in drivers/mfd provides common services for the
15	drivers which manage the specific hardware blocks. These services
16	include locking for common registers, clock control and resource
17	management.
19	The core registers drivers for both PCI and generic bus based
20	chips via the platform device and driver system.
22	On detection of a device, the core initialises the chip (which may
23	be specified by the platform data) and then exports the selected
24	peripheral set as platform devices for the specific drivers.
26	The core re-uses the platform device system as the platform device
27	system provides enough features to support the drivers without the
28	need to create a new bus-type and the associated code to go with it.
31	Resources
32	---------
34	Each peripheral has a view of the device which is implicitly narrowed to
35	the specific set of resources that peripheral requires in order to
36	function correctly.
38	The centralised memory allocation allows the driver to ensure that the
39	maximum possible resource allocation can be made to the video subsystem
40	as this is by-far the most resource-sensitive of the on-chip functions.
42	The primary issue with memory allocation is that of moving the video
43	buffers once a display mode is chosen. Indeed when a video mode change
44	occurs the memory footprint of the video subsystem changes.
46	Since video memory is difficult to move without changing the display
47	(unless sufficient contiguous memory can be provided for the old and new
48	modes simultaneously) the video driver fully utilises the memory area
49	given to it by aligning fb0 to the start of the area and fb1 to the end
50	of it. Any memory left over in the middle is used for the acceleration
51	functions, which are transient and thus their location is less critical
52	as it can be moved.
55	Configuration
56	-------------
58	The platform device driver uses a set of platform data to pass
59	configurations through to the core and the subsidiary drivers
60	so that there can be support for more than one system carrying
61	an SM501 built into a single kernel image.
63	The PCI driver assumes that the PCI card behaves as per the Silicon
64	Motion reference design.
66	There is an errata (AB-5) affecting the selection of the
67	of the M1XCLK and M1CLK frequencies. These two clocks
68	must be sourced from the same PLL, although they can then
69	be divided down individually. If this is not set, then SM501 may
70	lock and hang the whole system. The driver will refuse to
71	attach if the PLL selection is different.
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