2009-09-10 22:24:17     How to alloc right DMA memory in BF548?

2009-09-10 22:24:17     How to alloc right DMA memory in BF548?

Ray Zheng (CHINA)

Message: 79758   

Hi, everyone! our board uses bf548 and has two SAA7113 chips with 64M DRAM. I use kmalloc function to alloc memory for DMA, but the output video is mess, also I try to add a 'GFP_DMA' flag to be the second argument, but it doesn't make any imporment.

Through many experiments, I found it's right if the allocated memory is in the low address(less than 44M). but I don't know why, either I can't control if the address is in the low range. Your help will be appreciated greatly.

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2009-09-10 22:55:54     Re: How to alloc right DMA memory in BF548?

Yi Li (CHINA)

Message: 79761   

You may use dma_alloc_coherent() to allocate memory for DMA (and you need to make sure you have configured CONFIG_DMA_UNCACHED_*M).

-Yi

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2009-09-10 23:04:06     Re: How to alloc right DMA memory in BF548?

Yi Li (CHINA)

Message: 79762   

> I found it's right if the allocated memory is in the low address(less than 44M). but I don't know why,

There is only one memory zone - ZONE_DMA for blackfin,

If you don't want to use dma_alloc_coherent() to alloc from the uncached memory region, you may use dma_map_sg() or dma_map_single(). Please refer to arch/blackfin/kernel/dma-mapping.c for details.

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2009-09-14 21:50:55     Re: How to alloc right DMA memory in BF548?

Ray Zheng (CHINA)

Message: 79889   

Actually I have tried this function, but it doesn't work.  my DMA region is 2M as default.

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2009-09-14 22:38:54     Re: How to alloc right DMA memory in BF548?

Yi Li (CHINA)

Message: 79891   

What is the details of your problem?