[Intel-gfx] [PATCH v4 4/6] drm/i915/guc: (re)initialise doorbell h/w when enabling GuC submission

[Dave Gordon]

During a hibernate/resume cycle, the whole system is reset, including
the GuC and the doorbell hardware. Then the system is booted up, drivers
are loaded, etc -- the GuC firmware may be loaded and set running at this
point. But then, the booted kernel is replaced by the hibernated image,
and this resumed kernel will also try to reload the GuC firmware (which
will fail). To recover, we reset the GuC and try again (which should
work). But this GuC reset doesn't also reset the doorbell hardware, so
it can be left in a state inconsistent with that assumed by the driver
and the GuC.

It would be better if the GuC reset also cleared all doorbell state,
but that's not how the hardware currently works; also, the driver cannot
directly reprogram the doorbell hardware (only the GuC can do that).

So this patch cycles through all doorbells, assigning and releasing each
in turn, so that all the doorbell hardware is left in a consistent state,
no matter how it was programmed by the previously-running kernel and/or
GuC firmware.

This patch can be removed if/when the GuC firmware is updated so that it
(re)initialises the doorbell hardware after every firmware (re)load.

Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
---
 drivers/gpu/drm/i915/i915_guc_submission.c | 46 +++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 2fc69f1..f466eab 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -707,6 +707,50 @@ static void guc_client_free(struct drm_device *dev,
 	kfree(client);
 }
 
+/*
+ * Borrow the first client to set up & tear down every doorbell
+ * in turn, to ensure that all doorbell h/w is (re)initialised.
+ */
+static void guc_init_doorbell_hw(struct intel_guc *guc)
+{
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+	struct i915_guc_client *client = guc->execbuf_client;
+	struct guc_doorbell_info *doorbell;
+	uint16_t db_id, i;
+	void *base;
+	int ret;
+
+	base = kmap_atomic(i915_gem_object_get_page(client->client_obj, 0));
+	doorbell = base + client->doorbell_offset;
+	db_id = client->doorbell_id;
+
+	for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
+		i915_reg_t drbreg = GEN8_DRBREGL(i);
+		u32 value = I915_READ(drbreg);
+
+		ret = guc_update_doorbell_id(client, doorbell, i);
+
+		if (((value & GUC_DOORBELL_ENABLED) && (i != db_id)) || ret)
+			DRM_DEBUG_DRIVER("Doorbell reg 0x%x was 0x%x, ret %d\n",
+				drbreg.reg, value, ret);
+	}
+
+	/* Restore to original value */
+	guc_update_doorbell_id(client, doorbell, db_id);
+
+	for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
+		i915_reg_t drbreg = GEN8_DRBREGL(i);
+		u32 value = I915_READ(drbreg);
+
+		if ((value & GUC_DOORBELL_ENABLED) && (i != db_id))
+			DRM_DEBUG_DRIVER("Doorbell reg 0x%x finally 0x%x\n",
+						drbreg.reg, value);
+
+	}
+
+	kunmap_atomic(base);
+}
+
 /**
  * guc_client_alloc() - Allocate an i915_guc_client
  * @dev:	drm device
@@ -971,8 +1015,8 @@ int i915_guc_submission_enable(struct drm_device *dev)
 	}
 
 	guc->execbuf_client = client;
-
 	host2guc_sample_forcewake(guc, client);
+	guc_init_doorbell_hw(guc);
 
 	return 0;
 }
-- 
1.9.1