Subject: How to the the physical addresses under linux (au1500)

From: Sergio Ruiz <[email-masked]>
Date: Tue, 3 May 2005 21:56:26 +0200

I am trying to program  the DMA (with the ac97) in assembler using a
linux kernel module for mips teaching purposes.
The problem is that I need to get the physical address of the pointer
to the buffer to transfer to the AC97.
Looking at the kernel source code, I found that I can get the physical
address subtracting 0x8000000, but It doesnt seem to work.

Any idea?

Thanks,

Sergio

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From: Dan Malek <[email-masked]>
Date: Tue, 3 May 2005 16:09:58 -0400

> linux kernel module for mips teaching purposes.

I think you want to choose a more simple teaching example :-)

> address subtracting 0x8000000, but It doesnt seem to work.

Not always.  On systems like this one that are not cache coherent,
we play games with mapped addresses to get uncached spaces
or you need to apply various macros/functions to keep the space
coherent.

> Any idea?

Use a more simple example.  Maybe just update one of the
LED displays on the board.

	-- Dan