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. 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 | 35 +++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c index 70e9e40..cf35f01 100644 --- a/drivers/gpu/drm/i915/i915_gem_context.c +++ b/drivers/gpu/drm/i915/i915_gem_context.c @@ -351,7 +351,7 @@ mi_set_context(struct intel_ring_buffer *ring, struct i915_hw_context *new_context, u32 hw_flags) { - int ret; + int ret, len; /* w/a: If Flush TLB Invalidation Mode is enabled, driver must do a TLB * invalidation prior to MI_SET_CONTEXT. On GEN6 we don't set the value @@ -364,7 +364,16 @@ mi_set_context(struct intel_ring_buffer *ring, return ret; } - ret = intel_ring_begin(ring, 6); + len = 4; + switch (INTEL_INFO(ring->dev)->gen) { + case 7: + case 5: len += 2; + break; + } + if (!new_context->is_initialized) + len += 2; + + ret = intel_ring_begin(ring, len); if (ret) return ret; @@ -376,9 +385,22 @@ mi_set_context(struct intel_ring_buffer *ring, case 5: intel_ring_emit(ring, MI_SUSPEND_FLUSH | MI_SUSPEND_FLUSH_EN); break; - default: - intel_ring_emit(ring, MI_NOOP); - 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); @@ -398,9 +420,6 @@ mi_set_context(struct intel_ring_buffer *ring, case 5: intel_ring_emit(ring, MI_SUSPEND_FLUSH); break; - default: - intel_ring_emit(ring, MI_NOOP); - break; } intel_ring_advance(ring); -- 1.8.4.rc1 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
