[Nouveau] Second copy engine on GF116

[Andy Ritger]

On Fri, Nov 21, 2014 at 01:39:55AM -0500, Ilia Mirkin wrote:
> On Fri, Nov 21, 2014 at 1:16 AM, Andy Ritger <aritger at nvidia.com> wrote:
> > Hi Ilia,
> >
> > Actually 0x90b8 is different than copy engine.  I'm not very familiar
> > with it, but 0x90b8 is an engine for performing LZO decompression as
> > part of performing the copy.  It has a variety of limitations (e.g.,
> > cannot handle blocklinear format), and was only in a few Fermi chips,
> > as I understand it.
> 
> According to our driver source, GF100, GF104, GF110, GF114, and GF116
> all have it. [So GF106, GF108, GF117, GF119 don't have it.] We've only
> had problems reported against GF116... and only for some people.

Hmm, some of our internal documentation is inconsistent about whether it
applies to GF100, but otherwise what I see matches your list.  I guess
"few" was not entirely accurate.

> > It is probably easiest to just ignore it.  You can distinguish this
> > decompress engine from normal copy engine by looking at the CE capability
> > register on falcon (0x00000650).  If bit 2 is '1', then the falcon is
> > a decompress engine.
> 
> I presume you mean a +0x650 register on the pcopy engines (0x104000
> and 0x105000). I only have access to the GF108 right now, which
> returns 3 for 0x104650 and 4 for 0x105650. We're using the engine at
> 0x104000 for copy on the GF108...

Yes, 0x104650 and 0x105650 are the right addresses, from what I can tell.

FWIW, the other capability bits are:
bit 0: "DMACOPY_SUPPORTED"
bit 1: "PIXREMAP_SUPPORTED"

(I think PIXREMAP_SUPPORTED is in reference to the component remapping
controlled by methods 0x00000700, 0x00000704, and 0x00000708 in the
copy engine class).

> From my admittedly limited understanding, both 0x104000 and 0x105000
> appear to be falcon engines, where the fuc is presumably able to drive
> some underlying hardware. The actual fifo methods are implemented in
> the fuc, which in turn does iowr/etc commands.
>
> Are you saying that the "decompress" engine (at 0x105000 right?) has a
> different piece of hardware behind it than the copy engine at
> 0x104000, or does NVIDIA simply provide different fuc for it that
> exposes somewhat different functionality via FIFO methods?

There is definitely a falcon at the frontend, and there is different
falcon ucode for "normal" copy engine versus the "decompress" engine.
But, I don't know off hand what dedicated hardware, if any, is behind it.

- Andy


> >
> > I hope that helps,
> > - Andy
> >
> >
> > On Thu, Nov 20, 2014 at 02:18:02PM -0500, Ilia Mirkin wrote:
> >> Hello,
> >>
> >> There's a long-standing bug on nouveau (this is a sample bug, but the
> >> issue has been around for a while:
> >> https://bugs.freedesktop.org/show_bug.cgi?id=85465) whereby we attempt
> >> to use the second PCOPY engine on GF116, and it is sometimes does
> >> nothing, despite mmio register 22500 saying that it's not disabled
> >> (0x22500 == 0 for this user). In the bug you can see a dump from
> >> 22400..22600, and all values after 22440 are read as 0. The issue
> >> appears to be more common on mobile GF116's, but I don't know that the
> >> correlation is 100%. No errors are reported by the FIFO or invalid
> >> mmio reads, but the data transfer just does not happen. Switching to
> >> using the first copy engine resolves things, so it's unlikely to be a
> >> more systemic issue in nouveau's usage of the copy engine.
> >>
> >> To be clear, when I'm talking about the second PCOPY engine, I'm
> >> talking about the engine at mmio 0x105000, and whose fifo class id is
> >> 0x90b8.
> >>
> >> Any information on properly detecting that the engine is, in fact,
> >> missing, would be greatly appreciated. Or, conversely, an assurance
> >> that the engine _is_ there on all GF116's and we're just not
> >> initializing something properly, along with perhaps some suggestions
> >> as to what we might be missing.
> >>
> >> Thanks,
> >>
> >> Ilia Mirkin
> >> imirkin at alum.mit.edu
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