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

[Arvind R <arvino55-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, Mar 11, 2010 at 4:32 PM, Pekka Paalanen <pq-X3B1VOXEql0@public.gmane.org> wrote:
> 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);
>>
sorry for the typo and other procedural errors.
the last added line should be
+    vma->vm_page_prot = vm_get_page_prot(vma->vm_flags)

>> 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.
>
Efficacy of patch:
successful flightgear run on dom0 AND bareboot!

Arvind R.