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0001                         SM501 Driver
0002                         ============
0003 
0004 Copyright 2006, 2007 Simtec Electronics
0005 
0006 The Silicon Motion SM501 multimedia companion chip is a multifunction device
0007 which may provide numerous interfaces including USB host controller USB gadget,
0008 asynchronous serial ports, audio functions, and a dual display video interface.
0009 The device may be connected by PCI or local bus with varying functions enabled.
0010 
0011 Core
0012 ----
0013 
0014 The core driver in drivers/mfd provides common services for the
0015 drivers which manage the specific hardware blocks. These services
0016 include locking for common registers, clock control and resource
0017 management.
0018 
0019 The core registers drivers for both PCI and generic bus based
0020 chips via the platform device and driver system.
0021 
0022 On detection of a device, the core initialises the chip (which may
0023 be specified by the platform data) and then exports the selected
0024 peripheral set as platform devices for the specific drivers.
0025 
0026 The core re-uses the platform device system as the platform device
0027 system provides enough features to support the drivers without the
0028 need to create a new bus-type and the associated code to go with it.
0029 
0030 
0031 Resources
0032 ---------
0033 
0034 Each peripheral has a view of the device which is implicitly narrowed to
0035 the specific set of resources that peripheral requires in order to
0036 function correctly.
0037 
0038 The centralised memory allocation allows the driver to ensure that the
0039 maximum possible resource allocation can be made to the video subsystem
0040 as this is by-far the most resource-sensitive of the on-chip functions.
0041 
0042 The primary issue with memory allocation is that of moving the video
0043 buffers once a display mode is chosen. Indeed when a video mode change
0044 occurs the memory footprint of the video subsystem changes.
0045 
0046 Since video memory is difficult to move without changing the display
0047 (unless sufficient contiguous memory can be provided for the old and new
0048 modes simultaneously) the video driver fully utilises the memory area
0049 given to it by aligning fb0 to the start of the area and fb1 to the end
0050 of it. Any memory left over in the middle is used for the acceleration
0051 functions, which are transient and thus their location is less critical
0052 as it can be moved.
0053 
0054 
0055 Configuration
0056 -------------
0057 
0058 The platform device driver uses a set of platform data to pass
0059 configurations through to the core and the subsidiary drivers
0060 so that there can be support for more than one system carrying
0061 an SM501 built into a single kernel image.
0062 
0063 The PCI driver assumes that the PCI card behaves as per the Silicon
0064 Motion reference design.
0065 
0066 There is an errata (AB-5) affecting the selection of the
0067 of the M1XCLK and M1CLK frequencies. These two clocks
0068 must be sourced from the same PLL, although they can then
0069 be divided down individually. If this is not set, then SM501 may
0070 lock and hang the whole system. The driver will refuse to
0071 attach if the PLL selection is different.