Re: [Xen-devel] Re: Attempt to start X-Server at Xen 3.5 Dom0 ( 2.6.31) on top of Ubuntu 9.04 Server

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

On Wed, Sep 23, 2009 at 10:54:09PM -0700, Boris Derzhavets wrote:
> Sorry , there is difference in dmesg reports under xen and as vanilla.
> 
> dmesg under xen:-
> 
> [  243.858191] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [  243.858263] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [  244.132051] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [  244.132115] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [  244.132181] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [  244.157265] [drm] Setting GART location based on new memory map
> [  244.190885] [drm] Loading RV730/RV740 PFP Microcode
> [  244.190911] [drm] Loading RV730/RV740 CP Microcode
> [  244.205974] [drm] Resetting GPU
> ->    [  244.310103] [drm] writeback test failed
> [  251.220092] [drm] Resetting GPU
> 
> dmesg 2.6.31 vanilla:-
> 
> [   36.941430] [drm] Initialized drm 1.1.0 20060810
> [   36.988225] pci 0000:01:00.0: setting latency timer to 64
> [   36.988341] [drm] Initialized radeon 1.31.0 20080528 for 0000:01:00.0 on 
> minor 0
> [   36.989222] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [   37.210900] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [   37.210940] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [   37.210976] mtrr: type mismatch for d0000000,10000000 old: write-back new: 
> write-combining
> [   37.232744] [drm] Setting GART location based on new memory map
> [   37.248205] [drm] Loading RV730/RV740 PFP Microcode
> [   37.248227] [drm] Loading RV730/RV740 CP Microcode
> [   37.263281] [drm] Resetting GPU
> -> [   37.263336] [drm] writeback test succeeded in 1 usecs

I think I know why this is not working.

The DRM and its AGP modules call virt_to_gart and gart_to_virt, which is 
defined as:

#define virt_to_gart(x) (phys_to_gart(virt_to_phys(x)))
#define gart_to_virt(x) (phys_to_virt(gart_to_phys(x)))
and phys_to_gart and gart_to_phys are:
#define phys_to_gart(x) swiotlb_phys_to_bus(NULL, (x))
#define gart_to_phys(x) swiotlb_bus_to_phys(NULL, (x))

The swiotlb_* calls do return the wrong information when the
kernel is running under Xen.

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