[Nouveau] Second copy engine on GF116

[Andy Ritger]

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.

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 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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