Re: [Xen-devel] Nouveau on dom0

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Feb 26, 2010 at 09:04:33PM +0530, Arvind R wrote:
> On Thu, Feb 25, 2010 at 11:14 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Thu, Feb 25, 2010 at 09:01:48AM -0800, Arvind R wrote:
> >> On Thu, Feb 25, 2010 at 6:25 PM, Konrad Rzeszutek Wilk
> >> <konrad.wilk@xxxxxxxxxx> wrote:
> >> > On Thu, Feb 25, 2010 at 02:16:07PM +0530, Arvind R wrote:
> >> >> Hi all,
> >> >> I merged the drm-tree from 2.6.33-rc8 into jeremy's 2.6.31.6 master and
> >> ======= snip =======
> >> > is not. Would it be possible to trace down who allocates that *chan? You
> >> > say it is 'PRAMIN' - is that allocated via pci_alloc_* call?
> ======= snip =======
> >> So, there must be a mmap call somewhere to map the area to user-space
> >> for that problem write to work on non-Xen boots. Will try track down some 
> >> more
> >> and post. With mmaps and PCIGARTs - it will be some hunt!
>  ======= snip =======
> > to the drm_radeon driver which used it as a ring buffer. Took a bit of
> > hoping around to find who allocated it in the first place.
> >
> After a lot of reboots and log viewing:
> The pushbuf (FIFO/RING) is the only means of programming the card DMA
> activity. It is exposed to user-space by mmap of the drm_device (PCI) handle
> with different offsets for each channel. Parameters are associated to the DMA
> command using ioctls to bind channels/sub-channels/contexts. This mmap is
> in the libdrm2 library. Libdrm channel/accelerator  initialization and
> setup chores
>  and the DDX driver (xf86-video-nouveau) more-or-less acts thro' libdrm.

Ok, that is the DRM_NOUVEAU_CHANNEL_ALLOC ioctl, which ends up calling
the 'ttm_bo_init'. I remember Pasi having an issue with this on Radeon
and I provided a hack to see if it would work. Take a look at this
e-mail:

http://lists.xensource.com/archives/cgi-bin/extract-mesg.cgi?a=xen-devel&m=2010-01&i=20100115071856.GD17978%40reaktio.net

> 
> My suspicion is that Xen has some problems with mmap of PCI(E) device
> memory. How is iomem handled in a mmap?

It looks to be using 'ioremap' which is Xen safe. Unless your card has
an AGP bridge on it, at which point it would end up using
dma_alloc_coherent in all likehood. 

> 
> As of now, accelerator on Xen stops right at the initialisation stage - when
> libdrm tries to set up the accelerator-engine in the course of ScreenInit. And
> to do that, it cannot write the command to setup the basic 2D engine.

I think that the ttm_bo calls set up pages in the 4KB size, but the
initial channel requests a 64KB one. I think it also sets up 
page-table directory so that when the GPU accesses the addresses, it
gets the real bus address. I wonder if it fails at that thought -
meaning that the addresses that are written to the page table are
actually the guest page numbers (gpfn) instead of the machine page numbers 
(mfn).

The other issue might be that your back-port broke the AGP allocation.
It needs to be:
35 #define alloc_gatt_pages(order) ({ \
 36         char *_t; dma_addr_t _d; \
 37         _t = dma_alloc_coherent(NULL, PAGE_SIZE<<(order), &_d, GFP_KERNEL); 
\
 38         _t; })

But that is less likely.

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