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Commit | Line | Data |
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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 | Asyncronous 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. |