[PATCH 2/2] drm/i915/execlists: Clear STOP_RING bit before restoring the context

[Chris Wilson]

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c     | 15 +++++++++++++++
 drivers/gpu/drm/i915/intel_lrc_reg.h |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 3f90c74038ef..eb824eb18626 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1338,6 +1338,21 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 	GEM_BUG_ON(!intel_ring_offset_valid(ce->ring, ce->ring->head));
 	ce->lrc_reg_state[CTX_RING_HEAD+1] = ce->ring->head;
 
+	/*
+	 * After a reset the context may have preserved the STOP bit
+	 * of RING_MI_MODE we use to freeze an active engine before the
+	 * reset. If that bit is restored the ring stops instead of
+	 * executing.
+	 */
+	if (ce->lrc_reg_state[CTX_MI_MODE] == engine->mmio_base + 0x9c) {
+		pr_err("Found MI_MODE(%s): %08x [%s %s]\n", engine->name,
+		       ce->lrc_reg_state[CTX_MI_MODE + 1],
+		       (ce->lrc_reg_state[CTX_MI_MODE + 1] & MODE_IDLE) ? "idle" : "",
+		       (ce->lrc_reg_state[CTX_MI_MODE + 1] & STOP_RING) ? "stopped" : "");
+		ce->lrc_reg_state[CTX_MI_MODE + 1] |= STOP_RING << 16;
+		ce->lrc_reg_state[CTX_MI_MODE + 1] &= ~STOP_RING;
+	}
+
 	ce->state->obj->pin_global++;
 	i915_gem_context_get(ctx);
 	return ce;
diff --git a/drivers/gpu/drm/i915/intel_lrc_reg.h b/drivers/gpu/drm/i915/intel_lrc_reg.h
index 5ef932d810a7..3b155ecbfa92 100644
--- a/drivers/gpu/drm/i915/intel_lrc_reg.h
+++ b/drivers/gpu/drm/i915/intel_lrc_reg.h
@@ -39,6 +39,8 @@
 #define CTX_R_PWR_CLK_STATE		0x42
 #define CTX_END				0x44
 
+#define CTX_MI_MODE			0x54
+
 #define CTX_REG(reg_state, pos, reg, val) do { \
 	u32 *reg_state__ = (reg_state); \
 	const u32 pos__ = (pos); \
-- 
2.18.0