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Documentation/SM501.txt 2.79 KB
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  			SM501 Driver
  			============
  
  Copyright 2006, 2007 Simtec Electronics
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  The Silicon Motion SM501 multimedia companion chip is a multifunction device
  which may provide numerous interfaces including USB host controller USB gadget,
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  asynchronous serial ports, audio functions, and a dual display video interface.
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  The device may be connected by PCI or local bus with varying functions enabled.
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  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.