[Nouveau] TDMS bandwidth limits

[Francisco Jerez]

Edgar Fuß <ef at math.uni-bonn.de> writes:

> So my problem continues.
>
>> They're based on what the nvidia proprietary driver itself refuses to do,
> I see, thanks.
>
>> though, I'm not 100% sure that I had nv44 in my sample when I made that change.
> Looks like it limits to 155M in the nv44 case too, so your change is totally correct.
>
>> It might be using a reduced-blanking mode,
> Indeed it does, thanks. I had ruled out this too early as highly improbable.
>
>> check your Xorg.0.log to be sure. See the "-logverbose" option if you don't
>> get all the timings printed out with the default verbosity level.
> It does tell at least on level 9, thanks.
>
> However, what it doesn't tell is the timing actually used. Anyone more familiar with the relevant reverse engineering methods (MmioTrace or whatever) to find out?
>
A register dump [1] would be the easiest way to find out the exact
timings, but any standard 1600x1200 reduced-blanking mode should do it.

> The other problem is that nouveaufb doesn't (like matroxfb) provide a method of specifying the exact timing to use (and I would presumably need it in order not to change between FB console and X11).
>
You could just use the same CVT reduced-blanking mode on both X and the
framebuffer console.

> One would come to think that video=1600x1200RM would result in a reduced-blanking mode, but drm.debug=7 shows it actually does not.
> Reading the source of drm_fb_helper.c reveals that it's almost impossible to achieve rb=1.
>
Well, that works for me, can I have a look at your kernel logs?

> Any chance of implementing implicit reduced blanking in nouveau? If someone could hint me at where to architecturally correctly put it in I will be happy to start implementing it myself.
>
> I'm afraid more people than me will run into this and will regard the (absolutely plausible) TDMS bandwidth limiting as a regression ("Help! Help! My 1600x1200 used to work, but now it's broken!") when there's no reduced-blanking workaround.
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[1] http://cgit.freedesktop.org/~currojerez/tvdump/
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