[Nouveau] Help needed for bug 58556

[Pierre Moreau]

I think we had the wrong culprit: I just tried PCI-disabling the NVAC card (and keeping the NV96 one), and it just works: no garbage screen, and moreover, I get no hangs nor errors when enabling acceleration!

I'll spend some time comparing both outputs (without NVAC, and without NV96) to find out what the NVAC is doing wrong. 

Pierre

> On 31 Jan 2014, at 23:58, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> 
>> On Fri, Jan 31, 2014 at 5:39 PM,  <pierre.morrow at free.fr> wrote:
>> De: "Ilia Mirkin" <imirkin at alum.mit.edu>
>>> Unfortunately this is a *massive* bug... and confused by the "other"
>>> very similar but apparently not identical bug in the system.
>>> 
>>> What happens if you only enable acceleration on the NVAC card? (e.g.
>>> by hacking up nouveau to ignore the other one entirely). Wasn't there
>>> some thing where the NV96 card was effectively disabled but still
>>> appearing in PCI space? Or I might be thinking of a different mac
>>> situation...
>> 
>> Well, if I disable acceleration for the NV96 card, it doesn't hang after
>> initialising it, but I get spammed (I think it's PAGE_NOT_PRESENT errors,
>> like [1], but my screen goes garbage at that point, so I can't read
>> anything) later on, and I don't get to login.
> 
> I meant disable it much harder -- like tell nouveau to just ignore it
> as though modeset=0 was passed in for it. Also I seem to recall you
> can do an outb (even from grub) that will just turn off the nv96 card
> entirely.
> 
>> BTW, what could I do to get boot logs even if the system did not make it
>> trough (apart from recording with my phone...)?
> 
> pstore if you have efi, netconsole, blockconsole. And phone isn't so
> bad either :)
> 
>> 
>> 
>> 
>>> As you probably saw, this is a MASSIVE commit. What exactly was the
>>> problem with 20abd1634a?
>> 
>> The vblank structure was a little bit modified, and psw->vblank would be
>> initialised only when acceleration is on (it was always initialised before),
>> though it would be used inside functions called even when acceleration is
>> off. You can see it in comments 18 [2] and 20 [3].
>> 
>> 
>>> Can you go into some detail on what these tests were that yielded a
>>> successful outcome? IIRC nouveau_channel_new is called to create a
>>> new... channel, which is used by drm clients. If you don't have
>>> acceleration, that whole api is disabled, so it shouldn't come up. I
>>> guess accel_init also initializes drm->channel which is the kernel
>>> channel for doing stuff. [Although TBH I'm not entirely sure how
>>> things work without acceleration enabled...  but I think there's a
>>> non-fifo way to show images on the screen.]
>> 
>> My tests were pretty bruteforcing ones:
>> *   comment all nouveau_accel_init content, and uncomment block by block
>> until it works;
>> *   then comment all nouveau_channel_new content, and uncomment function by
>> function until it works;
>> *   and finally, I did the same inside nouveau_channel_init (for this
>> function, only the vram creation, gart creation and dma variables
>> initialisation were enough to get a clean screen).
>> 
>> To sum up what pieces of nouveau_accel_init were needed to get a clean
>> screen:
>> *   return if card is an NV96 one;
>> *   init fence;
>> *   run nouveau_channel_new:
>>    *   nouveau_channel_ind
>>    *   nouveau_channel_init, precisely these parts:
>>        *   vram creation;
>>        *   gart creation;
>>        *   dma variables initialisation.
> 
> Yeah, so all these things should only be necessary if you have
> acceleration enabled. I wonder if the card comes up in a funny "I'm
> still executing stuff" state and nouveau fails to "shut it down" when
> noaccel is passed in.
> 
>  -ilia