The extended state bits are stored in the LCA register and affect all updates to the LCA register - i.e. the state on the old context is saved when SAVE_EX_STATE_EN is currently set in the old context address before the update, and the new context is restored when RESTORE_EX_STATE_EN is set in the new context address. This is irrespective of the RESTORE_INHIBIT flag in the MI_SET_CONTEXT.
Hence, upon initial loading the contents of the extended state is read from uninitialised data. To workaround this, on first load we do a dummy load without the mandatory RESTORE_EX_STATE_EN bit so that the real load causes us to initialise the extended state of the context before it is then loaded by the LCA update. v2: Split out the introduction of the variable length MI_SET_CONTEXT command sequence. References: https://bugs.freedesktop.org/show_bug.cgi?id=64073 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Ben Widawsky <b...@bwidawsk.net> --- drivers/gpu/drm/i915/i915_gem_context.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c index 77400b9..2d2843e4 100644 --- a/drivers/gpu/drm/i915/i915_gem_context.c +++ b/drivers/gpu/drm/i915/i915_gem_context.c @@ -367,6 +367,8 @@ mi_set_context(struct intel_ring_buffer *ring, case 5: len += 2; break; } + if (!new_context->is_initialized) + len += 2; ret = intel_ring_begin(ring, len); if (ret) @@ -382,6 +384,22 @@ mi_set_context(struct intel_ring_buffer *ring, break; } + if (!new_context->is_initialized) { + /* The GPU tries to restore the extended state irrespective + * of RestoreInhibit (since it is part of the LCA switch + * itself rather than the MI_SET_CONTEXT command). + * Since the initial contents may be garbage we do a dummy + * load first then set the mandatory flag for any future + * ring context switches. + */ + intel_ring_emit(ring, MI_SET_CONTEXT); + intel_ring_emit(ring, + i915_gem_obj_ggtt_offset(new_context->obj) | + MI_MM_SPACE_GTT | + MI_SAVE_EXT_STATE_EN | + hw_flags); + } + intel_ring_emit(ring, MI_NOOP); intel_ring_emit(ring, MI_SET_CONTEXT); intel_ring_emit(ring, i915_gem_obj_ggtt_offset(new_context->obj) | -- 1.7.9.5 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
