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Linux/Documentation/SM501.txt

  1                         SM501 Driver
  2                         ============
  3 
  4 Copyright 2006, 2007 Simtec Electronics
  5 
  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.
 10 
 11 Core
 12 ----
 13 
 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.
 18 
 19 The core registers drivers for both PCI and generic bus based
 20 chips via the platform device and driver system.
 21 
 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.
 25 
 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.
 29 
 30 
 31 Resources
 32 ---------
 33 
 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.
 37 
 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.
 41 
 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.
 45 
 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.
 53 
 54 
 55 Configuration
 56 -------------
 57 
 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.
 62 
 63 The PCI driver assumes that the PCI card behaves as per the Silicon
 64 Motion reference design.
 65 
 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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