[Intel-gfx] [PATCH v2 21/21] drm/i915: Unify GPU resets upon shutdown

[Chris Wilson]

As we initialise engines, then contexts, ideally we want to unwind in
the opposite order: contexts then engines. Until now, the engines and
contexts were tightly coupled (the engine owned the default context)
preventing the "natural ordering" during shutdown. Now that execlists
merely holds a reference, as does the device for the kernel context, we
can relax the ordering constraint upon unload.

In doing so, we can reveal the true goal of this patch: always reset the GPU
back to its default starting condition before shutdown. It is known that
to disable the current legacy context we have to reset the GPU. The same
is true when the GPU has been enabled for execlists. However, we do each
reset separately, but functionally they are the same: Before shutting
down, we need to reset the GPU so that the next hardware user finds the
GPU in its expected default settings.

This unifies the resets added in a647828afc (drm/i915: Also perform gpu
reset under execlist mode) and 8e96d9c4d9 (drm/i915: reset the GPU on
context fini).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
CC: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: "Niu, Bing" <bing.niu at intel.com>
---
 drivers/gpu/drm/i915/i915_dma.c         | 37 ++++++++++++++++++++++++++-------
 drivers/gpu/drm/i915/i915_gem.c         |  8 -------
 drivers/gpu/drm/i915/i915_gem_context.c |  8 +------
 3 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 5c7615041b31..9aa4346b111a 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -425,6 +425,33 @@ static const struct vga_switcheroo_client_ops i915_switcheroo_ops = {
 	.can_switch = i915_switcheroo_can_switch,
 };
 
+static void i915_gem_fini(struct drm_device *dev)
+{
+	/*
+	 * Neither the BIOS, ourselves or any other kernel
+	 * expects the system to be in execlists mode on startup,
+	 * so we need to reset the GPU back to legacy mode. And the only
+	 * known way to disable logical contexts is through a GPU reset.
+	 *
+	 * So in order to leave the system in a known default configuration,
+	 * always reset the GPU upon unload. In the future, this will also
+	 * cleans up the GEM state tracking, flushing off the requests and
+	 * leaving the system in a known idle state.
+	 *
+	 * Note that is of the upmost importance that the GPU is idle and
+	 * all stray writes are flushed *before* we dismantle the backing
+	 * storage for the pinned objects.
+	 */
+	intel_gpu_reset(dev, ALL_ENGINES);
+
+	mutex_lock(&dev->struct_mutex);
+	i915_gem_context_fini(dev);
+	i915_gem_cleanup_engines(dev);
+	mutex_unlock(&dev->struct_mutex);
+
+	WARN_ON(!list_empty(&to_i915(dev)->context_list));
+}
+
 static int i915_load_modeset_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -506,10 +533,7 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	return 0;
 
 cleanup_gem:
-	mutex_lock(&dev->struct_mutex);
-	i915_gem_cleanup_engines(dev);
-	i915_gem_context_fini(dev);
-	mutex_unlock(&dev->struct_mutex);
+	i915_gem_fini(dev);
 cleanup_irq:
 	intel_guc_ucode_fini(dev);
 	drm_irq_uninstall(dev);
@@ -1456,10 +1480,7 @@ int i915_driver_unload(struct drm_device *dev)
 	flush_workqueue(dev_priv->wq);
 
 	intel_guc_ucode_fini(dev);
-	mutex_lock(&dev->struct_mutex);
-	i915_gem_cleanup_engines(dev);
-	i915_gem_context_fini(dev);
-	mutex_unlock(&dev->struct_mutex);
+	i915_gem_fini(dev);
 	intel_fbc_cleanup_cfb(dev_priv);
 
 	intel_power_domains_fini(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a88aa7f11a9c..82e41eeb36bb 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4970,14 +4970,6 @@ i915_gem_cleanup_engines(struct drm_device *dev)
 
 	for_each_engine(engine, dev_priv)
 		dev_priv->gt.cleanup_engine(engine);
-
-	if (i915.enable_execlists)
-		/*
-		 * Neither the BIOS, ourselves or any other kernel
-		 * expects the system to be in execlists mode on startup,
-		 * so we need to reset the GPU back to legacy mode.
-		 */
-		intel_gpu_reset(dev, ALL_ENGINES);
 }
 
 static void
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index fef33a3ce3b7..26122de365b2 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -452,14 +452,8 @@ void i915_gem_context_fini(struct drm_device *dev)
 
 	i915_gem_context_lost(dev_priv);
 
-	if (dctx->legacy_hw_ctx.rcs_state) {
-		/* The only known way to stop the gpu from accessing the hw context is
-		 * to reset it. Do this as the very last operation to avoid confusing
-		 * other code, leading to spurious errors. */
-		intel_gpu_reset(dev, ALL_ENGINES);
-
+	if (dctx->legacy_hw_ctx.rcs_state)
 		i915_gem_object_ggtt_unpin(dctx->legacy_hw_ctx.rcs_state);
-	}
 
 	i915_gem_context_unreference(dctx);
 	dev_priv->kernel_context = NULL;
-- 
2.8.1