linux/Documentation/SM501.txt
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   1                        SM501 Driver
   2                        ============
   3
   4Copyright 2006, 2007 Simtec Electronics
   5
   6The Silicon Motion SM501 multimedia companion chip is a multifunction device
   7which may provide numerous interfaces including USB host controller USB gadget,
   8asynchronous serial ports, audio functions, and a dual display video interface.
   9The device may be connected by PCI or local bus with varying functions enabled.
  10
  11Core
  12----
  13
  14The core driver in drivers/mfd provides common services for the
  15drivers which manage the specific hardware blocks. These services
  16include locking for common registers, clock control and resource
  17management.
  18
  19The core registers drivers for both PCI and generic bus based
  20chips via the platform device and driver system.
  21
  22On detection of a device, the core initialises the chip (which may
  23be specified by the platform data) and then exports the selected
  24peripheral set as platform devices for the specific drivers.
  25
  26The core re-uses the platform device system as the platform device
  27system provides enough features to support the drivers without the
  28need to create a new bus-type and the associated code to go with it.
  29
  30
  31Resources
  32---------
  33
  34Each peripheral has a view of the device which is implicitly narrowed to
  35the specific set of resources that peripheral requires in order to
  36function correctly.
  37
  38The centralised memory allocation allows the driver to ensure that the
  39maximum possible resource allocation can be made to the video subsystem
  40as this is by-far the most resource-sensitive of the on-chip functions.
  41
  42The primary issue with memory allocation is that of moving the video
  43buffers once a display mode is chosen. Indeed when a video mode change
  44occurs the memory footprint of the video subsystem changes.
  45
  46Since video memory is difficult to move without changing the display
  47(unless sufficient contiguous memory can be provided for the old and new
  48modes simultaneously) the video driver fully utilises the memory area
  49given to it by aligning fb0 to the start of the area and fb1 to the end
  50of it. Any memory left over in the middle is used for the acceleration
  51functions, which are transient and thus their location is less critical
  52as it can be moved.
  53
  54
  55Configuration
  56-------------
  57
  58The platform device driver uses a set of platform data to pass
  59configurations through to the core and the subsidiary drivers
  60so that there can be support for more than one system carrying
  61an SM501 built into a single kernel image.
  62
  63The PCI driver assumes that the PCI card behaves as per the Silicon
  64Motion reference design.
  65
  66There is an errata (AB-5) affecting the selection of the
  67of the M1XCLK and M1CLK frequencies. These two clocks
  68must be sourced from the same PLL, although they can then
  69be divided down individually. If this is not set, then SM501 may
  70lock and hang the whole system. The driver will refuse to
  71attach if the PLL selection is different.
  72
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