[Intel-gfx] [PATCH] drm/i915/cnl: WaPipeControlBefore3DStateSamplePattern

[Rafael Antognolli]

On Fri, Jan 26, 2018 at 09:55:58AM -0800, Rafael Antognolli wrote:
> On Fri, Jan 26, 2018 at 08:23:13AM +0000, Chris Wilson wrote:
> > Quoting Rafael Antognolli (2018-01-26 01:26:34)
> > > Write a PIPE_CONTROL with CS stall followed by 14 dwords of 0 in the
> > > indirect context wa bb.
> > 
> > 14 MI_NOOPS following? That isn't what you wrote in the code, but the
> 
> Agreed, sorry. The workarounds says:
> 
> 0x7a000004 0x00100000 + 14 dwords of 0. I counted 6 dwords from
> gen8_emit_pipe_control() and figured "just 8 more to 14". I think I had
> it right on my first version of this patch, but...
> 
> > main thing you haven't explained is why. A normal batch will already
> > have a flush in its setup, but more to the point would be the only
> > reason this is required is because of an implicit 3DSTATE inside the
> > context image on preemption. Right? Otherwise it seems to be a purely
> > userspace problem.
> 
> This is the text from the workaround:
> 
> "This bug can be hit on a context restore.  To avoid the issue the
> following must be programmed by SW to ensure the engine is idle prior to
> programming 3DSTATE_SAMPLE_PATTERN:
> 
> With RS context enabled: 0x21c8 = 0x000085c0
> 
> With RS context disabled:0x21c8 = 0x00001ac0
> 
> The above program specifes the offset to insert driver programmed
> commands
> 
> 0x21c4[31:6] = 0x<Addresses>
> 
> 0x21c4[5:0] = 0x<N>
> 
> N=Size of CL needed to fit Workaround
> 
> The above programming is the GGTT address of the driver programmed
> commands and the size(# of CL) to execute.
> 
> The address above needs to be a GGTT address and contain a pipe control
> with CS stall(0x7a000004 0x00100000 0x00000000 0x00000000)followed by
> 12DW’s of NOOP(0x00000000)"
> 
> Since it needs to be in a GGTT address, and it's specifically talking
> about the Indirect Context Pointer, we figured it should be in the
> kernel. I can update the commit message with the above text if it helps.
> 
> I originally implemented this trying to fix my GPU hang, but it turns
> out the issue was something else and this commit doesn't help at all.
> Still, I see no reason to not have it there just in case it prevent any
> future hangs...

Oh, and this workaround is actually a little longer, and there is a part
that describe a similar PIPE_CONTROL before 3DSTATE_SAMPLE_PATTERN. That
part is already implemented in userspace.