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1 | S3C2410 DMA | ||
2 | =========== | ||
3 | |||
4 | Introduction | ||
5 | ------------ | ||
6 | |||
7 | The kernel provides an interface to manage DMA transfers | ||
8 | using the DMA channels in the CPU, so that the central | ||
9 | duty of managing channel mappings, and programming the | ||
10 | channel generators is in one place. | ||
11 | |||
12 | |||
13 | DMA Channel Ordering | ||
14 | -------------------- | ||
15 | |||
16 | Many of the range do not have connections for the DMA | ||
17 | channels to all sources, which means that some devices | ||
18 | have a restricted number of channels that can be used. | ||
19 | |||
20 | To allow flexibility for each CPU type and board, the | ||
21 | DMA code can be given a DMA ordering structure which | ||
22 | allows the order of channel search to be specified, as | ||
23 | well as allowing the prohibition of certain claims. | ||
24 | |||
25 | struct s3c24xx_dma_order has a list of channels, and | ||
26 | each channel within has a slot for a list of DMA | ||
27 | channel numbers. The slots are searched in order for | ||
28 | the presence of a DMA channel number with DMA_CH_VALID | ||
29 | or-ed in. | ||
30 | |||
31 | If the order has the flag DMA_CH_NEVER set, then after | ||
32 | checking the channel list, the system will return no | ||
33 | found channel, thus denying the request. | ||
34 | |||
35 | A board support file can call s3c24xx_dma_order_set() | ||
36 | to register a complete ordering set. The routine will | ||
37 | copy the data, so the original can be discarded with | ||
38 | __initdata. | ||
39 | |||
40 | |||
41 | Authour | ||
42 | ------- | ||
43 | |||
44 | Ben Dooks, | ||
45 | Copyright (c) 2007 Ben Dooks, Simtec Electronics | ||
46 | Licensed under the GPL v2 | ||