Re: mm question

[volodya@mindspring.com]

On Mon, 10 Dec 2001, Alan Cox wrote:

> > "AGP addressable" memory which is ~64meg less than the total amount on my
> > machine. However, looking around in AGP driver or AGP specs does not seem
> > to indicate any restriction of the sort and, moreover, I do not need AGP
> > for this DMA transfer (it is PCI only).
> 
> Can the transfer go to pages mapped into the AGP gart, using their gart
> side mapping ?

Yes, but agpgart will not let more then one driver use it. So it will be
_either_ 3d or video capture with switching upon Xserver restart. Sucks !

> 
> > Better than giving up.. Unfortunately looking around in
> > linux/Documentation and drivers did not yield much in terms of
> > explanation. I know I can use mem_map_reserve to reserve a page but I
> > don't know how to get page struct from a physical address nor which lock
> > to use when messing with this.
> 
> You have to grab them at boot time via bootmem to get them in a range of

Does this imply that the driver must be compiled into the kernel ? In that
case I'll need to allocate at least 2meg of ram for each capture card..

> your choice. Otherwise you can use
> 
> 	get_free_page		-	grab a page
> 	virt_to_page		-	page struct of page
> 	virt_to_bus		-	bus addr of page
> 
> virt_to_bus isnt portable because real world pci bus mapping on non x86 is
> deeply murky and mysterious. But you probably want to worry about that
> after it works.

Yes, I almost went all the way rewriting the code in accordance with
DMA-mapping.txt thinking I am using "non-DMAable" memory or something 
until I noticed that all the functions are inlined to trivial for x86.

                           Vladimir Dergachev

> 
> Alan
>