drm/i915: preliminary context support

Very basic code for context setup/destruction in the driver.

Adds the file i915_gem_context.c This file implements HW context
support. On gen5+ a HW context consists of an opaque GPU object which is
referenced at times of context saves and restores.  With RC6 enabled,
the context is also referenced as the GPU enters and exists from RC6
(GPU has it's own internal power context, except on gen5).  Though
something like a context does exist for the media ring, the code only
supports contexts for the render ring.

In software, there is a distinction between contexts created by the
user, and the default HW context. The default HW context is used by GPU
clients that do not request setup of their own hardware context. The
default context's state is never restored to help prevent programming
errors. This would happen if a client ran and piggy-backed off another
clients GPU state.  The default context only exists to give the GPU some
offset to load as the current to invoke a save of the context we
actually care about. In fact, the code could likely be constructed,
albeit in a more complicated fashion, to never use the default context,
though that limits the driver's ability to swap out, and/or destroy
other contexts.

All other contexts are created as a request by the GPU client. These
contexts store GPU state, and thus allow GPU clients to not re-emit
state (and potentially query certain state) at any time. The kernel
driver makes certain that the appropriate commands are inserted.

There are 4 entry points into the contexts, init, fini, open, close.
The names are self-explanatory except that init can be called during
reset, and also during pm thaw/resume. As we expect our context to be
preserved across these events, we do not reinitialize in this case.

As Adam Jackson pointed out, The cutoff of 1MB where a HW context is
considered too big is arbitrary. The reason for this is even though
context sizes are increasing with every generation, they have yet to
eclipse even 32k. If we somehow read back way more than that, it
probably means BIOS has done something strange, or we're running on a
platform that wasn't designed for this.

v2: rename load/unload to init/fini (daniel)
remove ILK support for get_size() (indirectly daniel)
add HAS_HW_CONTEXTS macro to clarify supported platforms (daniel)
added comments (Ben)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>

drivers/gpu/drm/i915/Makefile

@@ -7,6 +7,7 @@ i915-y := i915_drv.o i915_dma.o i915_irq.o \
 	  i915_debugfs.o \
           i915_suspend.o \
 	  i915_gem.o \
+	  i915_gem_context.o \
 	  i915_gem_debug.o \
 	  i915_gem_evict.o \
 	  i915_gem_execbuffer.o \

drivers/gpu/drm/i915/i915_dma.c

@@ -1669,6 +1669,7 @@ int i915_driver_unload(struct drm_device *dev)
 	if (ret)
 		DRM_ERROR("failed to idle hardware: %d\n", ret);
 	i915_gem_retire_requests(dev);
+	i915_gem_context_fini(dev);
 	mutex_unlock(&dev->struct_mutex);
 
 	/* Cancel the retire work handler, which should be idle now. */
@@ -1758,6 +1759,8 @@ int i915_driver_open(struct drm_device *dev, struct drm_file *file)
 	spin_lock_init(&file_priv->mm.lock);
 	INIT_LIST_HEAD(&file_priv->mm.request_list);
 
+	i915_gem_context_open(dev, file);
+
 	return 0;
 }
 
@@ -1790,6 +1793,7 @@ void i915_driver_lastclose(struct drm_device * dev)
 
 void i915_driver_preclose(struct drm_device * dev, struct drm_file *file_priv)
 {
+	i915_gem_context_close(dev, file_priv);
 	i915_gem_release(dev, file_priv);
 }
 

drivers/gpu/drm/i915/i915_drv.c

@@ -903,6 +903,7 @@ int i915_reset(struct drm_device *dev)
 		for_each_ring(ring, dev_priv, i)
 			ring->init(ring);
 
+		i915_gem_context_init(dev);
 		i915_gem_init_ppgtt(dev);
 
 		mutex_unlock(&dev->struct_mutex);

drivers/gpu/drm/i915/i915_drv.h

@@ -821,6 +821,8 @@ typedef struct drm_i915_private {
 	struct drm_property *force_audio_property;
 
 	struct work_struct parity_error_work;
+	bool hw_contexts_disabled;
+	uint32_t hw_context_size;
 } drm_i915_private_t;
 
 /* Iterate over initialised rings */
@@ -1075,6 +1077,7 @@ struct drm_i915_file_private {
 #define HAS_LLC(dev)            (INTEL_INFO(dev)->has_llc)
 #define I915_NEED_GFX_HWS(dev)	(INTEL_INFO(dev)->need_gfx_hws)
 
+#define HAS_HW_CONTEXTS(dev)	(INTEL_INFO(dev)->gen >= 6)
 #define HAS_ALIASING_PPGTT(dev)	(INTEL_INFO(dev)->gen >=6)
 
 #define HAS_OVERLAY(dev)		(INTEL_INFO(dev)->has_overlay)
@@ -1363,6 +1366,11 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
 struct dma_buf *i915_gem_prime_export(struct drm_device *dev,
 				struct drm_gem_object *gem_obj, int flags);
 
+/* i915_gem_context.c */
+void i915_gem_context_init(struct drm_device *dev);
+void i915_gem_context_fini(struct drm_device *dev);
+void i915_gem_context_open(struct drm_device *dev, struct drm_file *file);
+void i915_gem_context_close(struct drm_device *dev, struct drm_file *file);
 
 /* i915_gem_gtt.c */
 int __must_check i915_gem_init_aliasing_ppgtt(struct drm_device *dev);

drivers/gpu/drm/i915/i915_gem.c

@@ -3714,6 +3714,11 @@ i915_gem_init_hw(struct drm_device *dev)
 
 	dev_priv->next_seqno = 1;
 
+	/*
+	 * XXX: There was some w/a described somewhere suggesting loading
+	 * contexts before PPGTT.
+	 */
+	i915_gem_context_init(dev);
 	i915_gem_init_ppgtt(dev);
 
 	return 0;

drivers/gpu/drm/i915/i915_gem_context.c

+/*
+ * Copyright © 2011-2012 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ *    Ben Widawsky <ben@bwidawsk.net>
+ *
+ */
+
+/*
+ * This file implements HW context support. On gen5+ a HW context consists of an
+ * opaque GPU object which is referenced at times of context saves and restores.
+ * With RC6 enabled, the context is also referenced as the GPU enters and exists
+ * from RC6 (GPU has it's own internal power context, except on gen5). Though
+ * something like a context does exist for the media ring, the code only
+ * supports contexts for the render ring.
+ *
+ * In software, there is a distinction between contexts created by the user,
+ * and the default HW context. The default HW context is used by GPU clients
+ * that do not request setup of their own hardware context. The default
+ * context's state is never restored to help prevent programming errors. This
+ * would happen if a client ran and piggy-backed off another clients GPU state.
+ * The default context only exists to give the GPU some offset to load as the
+ * current to invoke a save of the context we actually care about. In fact, the
+ * code could likely be constructed, albeit in a more complicated fashion, to
+ * never use the default context, though that limits the driver's ability to
+ * swap out, and/or destroy other contexts.
+ *
+ * All other contexts are created as a request by the GPU client. These contexts
+ * store GPU state, and thus allow GPU clients to not re-emit state (and
+ * potentially query certain state) at any time. The kernel driver makes
+ * certain that the appropriate commands are inserted.
+ *
+ * The context life cycle is semi-complicated in that context BOs may live
+ * longer than the context itself because of the way the hardware, and object
+ * tracking works. Below is a very crude representation of the state machine
+ * describing the context life.
+ *                                         refcount     pincount     active
+ * S0: initial state                          0            0           0
+ * S1: context created                        1            0           0
+ * S2: context is currently running           2            1           X
+ * S3: GPU referenced, but not current        2            0           1
+ * S4: context is current, but destroyed      1            1           0
+ * S5: like S3, but destroyed                 1            0           1
+ *
+ * The most common (but not all) transitions:
+ * S0->S1: client creates a context
+ * S1->S2: client submits execbuf with context
+ * S2->S3: other clients submits execbuf with context
+ * S3->S1: context object was retired
+ * S3->S2: clients submits another execbuf
+ * S2->S4: context destroy called with current context
+ * S3->S5->S0: destroy path
+ * S4->S5->S0: destroy path on current context
+ *
+ * There are two confusing terms used above:
+ *  The "current context" means the context which is currently running on the
+ *  GPU. The GPU has loaded it's state already and has stored away the gtt
+ *  offset of the BO. The GPU is not actively referencing the data at this
+ *  offset, but it will on the next context switch. The only way to avoid this
+ *  is to do a GPU reset.
+ *
+ *  An "active context' is one which was previously the "current context" and is
+ *  on the active list waiting for the next context switch to occur. Until this
+ *  happens, the object must remain at the same gtt offset. It is therefore
+ *  possible to destroy a context, but it is still active.
+ *
+ */
+
+#include "drmP.h"
+#include "i915_drm.h"
+#include "i915_drv.h"
+
+static int get_context_size(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	int ret;
+	u32 reg;
+
+	switch (INTEL_INFO(dev)->gen) {
+	case 6:
+		reg = I915_READ(CXT_SIZE);
+		ret = GEN6_CXT_TOTAL_SIZE(reg) * 64;
+		break;
+	case 7:
+		reg = I915_READ(GEN7_CTX_SIZE);
+		ret = GEN7_CTX_TOTAL_SIZE(reg) * 64;
+		break;
+	default:
+		BUG();
+	}
+
+	return ret;
+}
+
+/**
+ * The default context needs to exist per ring that uses contexts. It stores the
+ * context state of the GPU for applications that don't utilize HW contexts, as
+ * well as an idle case.
+ */
+static int create_default_context(struct drm_i915_private *dev_priv)
+{
+	return 0;
+}
+
+void i915_gem_context_init(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t ctx_size;
+
+	if (!HAS_HW_CONTEXTS(dev))
+		return;
+
+	/* If called from reset, or thaw... we've been here already */
+	if (dev_priv->hw_contexts_disabled)
+		return;
+
+	ctx_size = get_context_size(dev);
+	dev_priv->hw_context_size = get_context_size(dev);
+	dev_priv->hw_context_size = round_up(dev_priv->hw_context_size, 4096);
+
+	if (ctx_size <= 0 || ctx_size > (1<<20)) {
+		dev_priv->hw_contexts_disabled = true;
+		return;
+	}
+
+	if (create_default_context(dev_priv)) {
+		dev_priv->hw_contexts_disabled = true;
+		return;
+	}
+
+	DRM_DEBUG_DRIVER("HW context support initialized\n");
+}
+
+void i915_gem_context_fini(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (dev_priv->hw_contexts_disabled)
+		return;
+}
+
+void i915_gem_context_open(struct drm_device *dev, struct drm_file *file)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (dev_priv->hw_contexts_disabled)
+		return;
+}
+
+void i915_gem_context_close(struct drm_device *dev, struct drm_file *file)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (dev_priv->hw_contexts_disabled)
+		return;
+}