linuxdc-dev

[linuxdc-dev] Maple DMA

[Adrian M. <ad...@mc...>]

I am working on a rewrite of the Maple code in the Linux SH repository.

I want the maple bus to query port on start up to determine which devices=
 are=20
initally attached. So I am building the various MAPLE_COMMAND_DEVINFO buf=
fers=20
to send. Going along slowly, learning as I do it...

But I am wondering what the code below (in the existing driver) does as I=
 have=20
to say my knowledge of DMA is shady


=09for (i=3D0; i<(1<<MAPLE_DMA_PAGES); i++)
=09=09=09dma_cache_wback_inv(maple_sendbuf+i*PAGE_SIZE, PAGE_SIZE);
=09=09

Could someone fill me in?

Thanks

Adrian

[linuxdc-dev] Re: [linuxsh-dev] Maple DMA

[Alex B. <ker...@be...>]

On Sun, 2004-06-20 at 19:15, Adrian McMenamin wrote:
> 	for (i=0; i<(1<<MAPLE_DMA_PAGES); i++)
> 			dma_cache_wback_inv(maple_sendbuf+i*PAGE_SIZE, PAGE_SIZE);
> 		
> 
> Could someone fill me in?

It invalidates the cache lines for the buffer you are DMA'ing so if you
read or write a value to the buffer post DMA it forces the processor to
pick up the value from memory instead of using the internal cache.

Otherwise weirdness can ensue...

-- 
Alex, Kernel Hacker: http://www.bennee.com/~alex/

Hackers are just a migratory lifeform with a tropism for computers.