Re: [Dri-devel] PPC Lockup (ati-pcigart-branch)

Dan Malek wrote:

Jeff Hartmann wrote:

quoted

Okay let me try and explain things a little better.

Got it.  That is what I was guessing, only surprised you are holding
page structs, but that makes sense.

quoted

......  Currently there is no kernel function to do
this explicitly

I'm working on that.  The PowerPC port cheated by using BATs and
trivial macros, but this doesn't work on some of the newer processors
and more complex applications.  Other architectures did the same, and
I am surprised there aren't generic kernel functions to track down this
information.  In fact, these functions are already present for 4xx and
8xx processors, so don't write anything new.

quoted

Another thing that happens later is that we need the bus address of each
of these pages to program the card to do scatter gather dma from this
region.

That's where this is going to fall apart on PowerPC.

quoted

.....  We do virt_to_bus(pagelist[i]->virtual) to accomplish this
translation.

I have to write some code (or actually remove some #ifdefs) before
this will work for you.

quoted

I know on the ia32 a pgd/pmd can actually point to 4MB pages rather then
a real pte.  Does the PowerPC have anything like this?

Not yet.  It's on the way....

quoted

....  I would doubt
that I would encounter anything like this from a vmalloc'ed area of
memory (since vmalloc is arch independent and it would call alloc_page
for each individual pte.)  Am I correct in this assumption?

Yes.

quoted

Just FYI, the code I posted works fine on the ia32 platform (only tested
with the i386 classic 2-level page tables.)

What you are doing so far should work too on PowerPC.

quoted

Another thing we might be running into here is that vmalloc does not
guarantee a virtually contiguous area of memory (or so I am told.)

Ummm...of course it is virtually contiguous.  How could it be
different?  You request a size, and it returns a base virtual address.
If there were holes in it, how would you know?

Look at vread in vmalloc.c, I think it would handle holes in a
vmalloc'ed area (From a brief reading of the code.)  I've seen postings
about this on linux-kernel.  I don't see a vwrite implementation, but I
would assume you would have to do something similar for writes.

quoted

.....  I've
NEVER seen this in practice on an ia32 platform.

It can't happen on any platform (or I don't understand something about
the comment, which could very well be the case today).

I think it can, I've seen numerous people talk about it on
linux-kernel.  I've also been told that my /dev/agpgart isn't 'safe'
because it assumes vmalloc'ed memory is always virtually contiguous.  I
think this only happens when there isn't enough virtual address space in
the kernel and its fragmented (probably only happens on machines with
lots of memory.)

-Jeff


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