On Thu, Jun 12, 2014 at 08:25:52AM -0700, Ben Widawsky wrote:
> On GEN8 the PDPs are saved and restored with context, which means we
> must set them after the context switch has occurred. If we do not do
> this, we end up saving the new PDPs for the old context.
>
> Example of a problem
> LRI PDPs 1
> MI_SET_CONTEXT bar
> LRI_PDPs 2
> MI_SET_CONTEXT foo // save PDPs 2 to bar's context
> // load foos PDPs
> LRI PDPs 1
> MI_SET_CONTEXT bar // save PDPs 1 to foo's context
>
> It's all wacky. This should allow full PPGTT on Broadwell to work.
Hmm. I had this impression too but now I'm not sure. The PDPs are listed
as being in the execlist context. Do we save/restore that in ring buffer
mode too? IIRC on ivb/hsw it got skipped.
And if the PDPs are really part of the context we shouldn't need to
load them at all I think, except when we skip the restore (unitialized
or default context). Or am I missing something here?
And what about ivb/hsw? Doesn't this reordering risk the context restore
accessing the wrong PPGTT. That's assuming the context restore can
already chase some pointers.
>
> Signed-off-by: Ben Widawsky <ben@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_context.c | 24 ++++++++++++++++++------
> 1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 3ffe308..b2434e0 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -623,13 +623,12 @@ static int do_switch(struct intel_engine_cs *ring,
> */
> from = ring->last_context;
>
> - if (USES_FULL_PPGTT(ring->dev)) {
> - ret = ppgtt->switch_mm(ppgtt, ring, false);
> - if (ret)
> - goto unpin_out;
> - }
> -
> if (ring != &dev_priv->ring[RCS]) {
> + if (USES_FULL_PPGTT(ring->dev)) {
> + ret = ppgtt->switch_mm(ppgtt, ring, false);
> + if (ret)
> + goto unpin_out;
> + }
> if (from)
> i915_gem_context_unreference(from);
> goto done;
> @@ -660,6 +659,19 @@ static int do_switch(struct intel_engine_cs *ring,
> if (ret)
> goto unpin_out;
>
> + if (USES_FULL_PPGTT(ring->dev)) {
> + ret = ppgtt->switch_mm(ppgtt, ring, false);
> + /* The hardware context switch is emitted, but we haven't
> + * actually changed the state - so it's probably safe to bail
> + * here. Still, let the user know something dangerous has
> + * happened.
> + */
> + if (ret) {
> + DRM_ERROR("Failed to change address space on context switch\n");
> + goto unpin_out;
> + }
> + }
> +
> for (i = 0; i < MAX_L3_SLICES; i++) {
> if (!(to->remap_slice & (1<<i)))
> continue;
> --
> 2.0.0
>
> _______________________________________________
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Ville Syrjälä
Intel OTC
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