sm501.rst (2902B)
1.. include:: <isonum.txt> 2 3============ 4SM501 Driver 5============ 6 7:Copyright: |copy| 2006, 2007 Simtec Electronics 8 9The Silicon Motion SM501 multimedia companion chip is a multifunction device 10which may provide numerous interfaces including USB host controller USB gadget, 11asynchronous serial ports, audio functions, and a dual display video interface. 12The device may be connected by PCI or local bus with varying functions enabled. 13 14Core 15---- 16 17The core driver in drivers/mfd provides common services for the 18drivers which manage the specific hardware blocks. These services 19include locking for common registers, clock control and resource 20management. 21 22The core registers drivers for both PCI and generic bus based 23chips via the platform device and driver system. 24 25On detection of a device, the core initialises the chip (which may 26be specified by the platform data) and then exports the selected 27peripheral set as platform devices for the specific drivers. 28 29The core re-uses the platform device system as the platform device 30system provides enough features to support the drivers without the 31need to create a new bus-type and the associated code to go with it. 32 33 34Resources 35--------- 36 37Each peripheral has a view of the device which is implicitly narrowed to 38the specific set of resources that peripheral requires in order to 39function correctly. 40 41The centralised memory allocation allows the driver to ensure that the 42maximum possible resource allocation can be made to the video subsystem 43as this is by-far the most resource-sensitive of the on-chip functions. 44 45The primary issue with memory allocation is that of moving the video 46buffers once a display mode is chosen. Indeed when a video mode change 47occurs the memory footprint of the video subsystem changes. 48 49Since video memory is difficult to move without changing the display 50(unless sufficient contiguous memory can be provided for the old and new 51modes simultaneously) the video driver fully utilises the memory area 52given to it by aligning fb0 to the start of the area and fb1 to the end 53of it. Any memory left over in the middle is used for the acceleration 54functions, which are transient and thus their location is less critical 55as it can be moved. 56 57 58Configuration 59------------- 60 61The platform device driver uses a set of platform data to pass 62configurations through to the core and the subsidiary drivers 63so that there can be support for more than one system carrying 64an SM501 built into a single kernel image. 65 66The PCI driver assumes that the PCI card behaves as per the Silicon 67Motion reference design. 68 69There is an errata (AB-5) affecting the selection of the 70of the M1XCLK and M1CLK frequencies. These two clocks 71must be sourced from the same PLL, although they can then 72be divided down individually. If this is not set, then SM501 may 73lock and hang the whole system. The driver will refuse to 74attach if the PLL selection is different.