Re: [Patch RFC] ttm: nouveau accelerated on Xen pv-ops kernel

[Pekka Paalanen <pq-X3B1VOXEql0@public.gmane.org>]

I'm adding dri-devel@ to CC, since this suggested patch touches
TTM code, and none of the Nouveau code. TTM patches go via
dri-devel@.

Thanks.


On Wed, 10 Mar 2010 18:51:21 +0530
Arvind R <arvino55-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> Hi,
> Following is a simple patch that is needed in nouveau to get
> accelerated X on a Xen dom0 pv_ops kernel. The kernel is jeremy's
> 2.6.31.6 as of 20100222. The whole gpu tree of nouveau (which is
> almost the mainline merge), was substituted into the kernel-tree.
> All components of X (mesa, Xorg-server-7.5, xf86-nouveau, libdrm)
> used of the same day.
> 
> Patch:
> diff -Naur nouveau-kernel.orig/drivers/gpu/drm/ttm/ttm_bo_vm.c
> nouveau-kernel.new/drivers/gpu/drm/ttm/ttm_bo_vm.c
> --- nouveau-kernel.orig/drivers/gpu/drm/ttm/ttm_bo_vm.c 2010-01-27
> 10:19:28.000000000 +0530
> +++ nouveau-kernel.new/drivers/gpu/drm/ttm/ttm_bo_vm.c  2010-03-10
> 17:28:59.000000000 +0530
> @@ -271,7 +271,10 @@
>          */
> 
>         vma->vm_private_data = bo;
> -       vma->vm_flags |= VM_RESERVED | VM_IO | VM_MIXEDMAP |
> VM_DONTEXPAND;
> +       vma->vm_flags |= VM_RESERVED | VM_MIXEDMAP |
> VM_DONTEXPAND;
> +       if (!((bo->mem.placement & TTM_PL_MASK_MEM) &
> TTM_PL_FLAG_TT))
> +               vma->vm_flags |= VM_IO;
> +       vma->vm_page_prot = vma_get_vm_prot(vma->vm_flags);
>         return 0;
>  out_unref:
>         ttm_bo_unref(&bo);
> 
> This patch is necessary because, in Xen, PFN of a page is
> virtualised. So physical addresses
> for DMA programming needs to use the MFN. Xen transparently does
> the correct translation
> using the _PAGE_IOMEM prot-bit in the PTE. If the bit is set,
> then Xen assumes that the backing
> memory is in the IOMEM space, and PFN equals MFN. If not set,
> page_to_pfn() returns MFN.
> 
> The patch enables the ttm_bo_vm_fault() handler to behave
> correctly under Xen, and has no
> side-effects on normal (not under Xen) operations. The use of
> TTM_PL_FLAG_TT in the
> check assumes that all other placements are backed by device
> memory or IO. If there are
> any other placements that use system memory, that flag has to be
> OR'ed into the check.
> 
> The above patch has no implications on a normal kernel or a Xen
> pv_ops kernel booted without
> the Xen hypervisor. My testing is on a debian-lenny environment
> on a Core2 processor with
> nVidia GeForce 9400 GT.

-- 
Pekka Paalanen
http://www.iki.fi/pq/