Hello all,
i have recently implemented some patches to the drm core and to the
intel and radeon kms drivers to provide high precision timestamping of
vblank intervals and for timestamping of pageflip bufferswap completion.
This is needed to properly implement the DRI2 sync & swap bits and their
support for the oml_sync_control extension.
The patches are in drm-next and will hopefully land in the 2.6.38 merge
window. Now i'd like to add support for the nouveau kms driver as well.
I had a look at the current nouveau code in drm-next. Implementing the
patches shouldn't be a problem, it is mostly copy & paste from
radeon/intel kms + a little bit of adjustments and then testing.
Problem: The code needs to query the current video scanout position of a
given crtc. My missing bit of information is the location and format of
the MMIO registers which presumably exist on nvidia gpu's to provide
this information. I know the gpu's support this, because the NVidia
proprietary drivers on both MS-Windows and MacOS/X provide a function to
query this info from userspace (Windows DirectDraw-7 GetScanline()
function, OS/X CGDisplayBeamposition() function). Unfortunately the
nvidia blob on Linux (and Linux/X11 itself) to my knowledge doesn't
support such an api, so i can't simply mmio-trace the blob to find the
relevant register. Also afaik the rules-ng database and the current
driver source code don't document the location of such a register.
I've already made friendship with renouveau and hacked it a bit for my
purpose, but playing with it for an hour on a Geforce 8800 and staring
at dumps didn't get me lucky that easily.
I thought i'd ask if any of you have by accident stumbled across such a
register or would have any good hints how i could narrow down the
search. Otherwise i'll hack up renouveau to do a bit of pattern
matching, searching for characteristic patterns in the brute force way
and praying to the gods of computing that this won't take forever. To my
surprise I already had to learn that apparently just reading the wrong
registers can cause display corruption and crash the whole machine.
Any helpful comments highly appreciated.
Thanks,
-mario
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