[haiku-commits] Re: r37068 - haiku/trunk/src/system/kernel/arch/x86

Ingo Weinhold <ingo_weinhold@xxxxxx> wrote:
> On 2010-06-09 at 14:12:33 [+0200], Axel Dörfler <axeld@xxxxxxxxxxxxxxxx>
> > wrote:
> > Apart from the earliest 64 bit machines, all of the current ones
> > should
> > have a dedicated MMU for PCI devices.
> That would be helpful indeed. Haven't spotted it in the specs yet,
> though.

Maybe this brings something to light (it seems to be machine
dependent): http://en.wikipedia.org/wiki/IOMMU

> > If that isn't available, and the
> > pages used lie outside the 4 GB range, a bounce buffer has to be
> > used.
> > Our DMAResource implementation should be able to deliver this all
> > one
> > day, but it will have to be used by all drivers that need its
> > functionality.
> ATM I don't see how you intend to extend DMAResource that it can be
> used
> for e.g. audio and network drivers. Those seem to mostly allocate
> contiguous RAM and write its physical address into some hardware
> register(s), which might only be 32 bit wide. The only thing that I
> can
> imagine to help (besides the dedicated MMU) is to somehow make sure
> that no
> memory beyond the 4 GB limit is allocated.

Drivers that only use their own buffers (which most network drivers we
have do), would indeed only need buffers below that limit. Since this
is a TODO item in dma_resources.cpp, too, maybe we could just have a
create_area_etc() that takes a dma_restrictions as argument?

Bye,
   Axel.


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