Re: dvd kernelmodule: memory address problem

On Wed, Apr 14, 2004 at 06:44:55PM +0200, JockyW wrote:
> Thanks for your assistance Arthur,
> 
> My simple dvd characterdevice works quite well. I rewrote the linux IRQ2
> handler to handle all dvd irqs (not just the cover int).

Block device, you mean ;)

> But now I stumbled on a memory problem. My devicedriver uses a read buffer
> which is a 2048 bytes static char array. When I print the address, it sits
> on 0xC200EB24. That address doesn't work when I pass it to the DMA Memory
> Address Register. It is a strange address, because in "yagcd"
> http://www.gc-linux.org/docs/yagcd/chap4.html#sec4 it is written that
> uncached logical ram addresses run from 0xc0000000-0xc17fffff
> 
> What kind of address translation should I apply to get the dma to work?

You want to use memory allocated from a dma pool for that instead.

Create one with:

struct dma_pool *dma_pool_create(const char *name, struct device *dev,
			size_t size, size_t align, size_t alloc);

Allocate memory from it with:

void *dma_pool_alloc(struct dma_pool *pool, int gfp_flags,
			dma_addr_t *dma_handle);

Free alloc'd memory with dma_pool_free(), destroy the pool with
dma_pool_destroy().

See drivers/base/dmapool.c and Documentation/DMA-API.txt for
the gory details.

	Arthur


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