drm/i915: Implement a framework for batch buffer pools

This adds a small module for managing a pool of batch buffers.
The only current use case is for the command parser, as described
in the kerneldoc in the patch. The code is simple, but separating
it out makes it easier to change the underlying algorithms and to
extend to future use cases should they arise.

The interface is simple: init to create an empty pool, fini to
clean it up, get to obtain a new buffer. Note that all buffers are
expected to be inactive before cleaning up the pool.

Locking is currently based on the caller holding the struct_mutex.
We already do that in the places where we will use the batch pool
for the command parser.

v2:
- s/BUG_ON/WARN_ON/ for locking assertions
- Remove the cap on pool size
- Switch from alloc/free to init/fini

v3:
- Idiomatic looping structure in _fini
- Correct handling of purged objects
- Don't return a buffer that's too much larger than needed

v4:
- Rebased to latest -nightly

v5:
- Remove _put() function and clean up comments to match

v6:
- Move purged check inside the loop (danvet, from v4 1/7 feedback)

v7:
- Use single list instead of two. (Chris W)
- s/active_list/cache_list
- Squashed in debug patches (Chris W)
  drm/i915: Add a batch pool debugfs file

  It provides some useful information about the buffers in
  the global command parser batch pool.

  v2: rebase on global pool instead of per-ring pools
  v3: rebase

  drm/i915: Add batch pool details to i915_gem_objects debugfs

  To better account for the potentially large memory consumption
  of the batch pool.

v8:
- Keep cache in LRU order (danvet, from v6 1/5 feedback)

Issue: VIZ-4719
Signed-off-by: Brad Volkin <bradley.d.volkin@intel.com>
Reviewed-By: Jon Bloomfield <jon.bloomfield@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 135 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_batch_pool.c b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
new file mode 100644
index 000000000000..6016125a4d1e
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
@@ -0,0 +1,135 @@
+/*
+ * Copyright © 2014 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.
+ *
+ */
+
+#include "i915_drv.h"
+
+/**
+ * DOC: batch pool
+ *
+ * In order to submit batch buffers as 'secure', the software command parser
+ * must ensure that a batch buffer cannot be modified after parsing. It does
+ * this by copying the user provided batch buffer contents to a kernel owned
+ * buffer from which the hardware will actually execute, and by carefully
+ * managing the address space bindings for such buffers.
+ *
+ * The batch pool framework provides a mechanism for the driver to manage a
+ * set of scratch buffers to use for this purpose. The framework can be
+ * extended to support other uses cases should they arise.
+ */
+
+/**
+ * i915_gem_batch_pool_init() - initialize a batch buffer pool
+ * @dev: the drm device
+ * @pool: the batch buffer pool
+ */
+void i915_gem_batch_pool_init(struct drm_device *dev,
+			      struct i915_gem_batch_pool *pool)
+{
+	pool->dev = dev;
+	INIT_LIST_HEAD(&pool->cache_list);
+}
+
+/**
+ * i915_gem_batch_pool_fini() - clean up a batch buffer pool
+ * @pool: the pool to clean up
+ *
+ * Note: Callers must hold the struct_mutex.
+ */
+void i915_gem_batch_pool_fini(struct i915_gem_batch_pool *pool)
+{
+	WARN_ON(!mutex_is_locked(&pool->dev->struct_mutex));
+
+	while (!list_empty(&pool->cache_list)) {
+		struct drm_i915_gem_object *obj =
+			list_first_entry(&pool->cache_list,
+					 struct drm_i915_gem_object,
+					 batch_pool_list);
+
+		WARN_ON(obj->active);
+
+		list_del_init(&obj->batch_pool_list);
+		drm_gem_object_unreference(&obj->base);
+	}
+}
+
+/**
+ * i915_gem_batch_pool_get() - select a buffer from the pool
+ * @pool: the batch buffer pool
+ * @size: the minimum desired size of the returned buffer
+ *
+ * Finds or allocates a batch buffer in the pool with at least the requested
+ * size. The caller is responsible for any domain, active/inactive, or
+ * purgeability management for the returned buffer.
+ *
+ * Note: Callers must hold the struct_mutex
+ *
+ * Return: the selected batch buffer object
+ */
+struct drm_i915_gem_object *
+i915_gem_batch_pool_get(struct i915_gem_batch_pool *pool,
+			size_t size)
+{
+	struct drm_i915_gem_object *obj = NULL;
+	struct drm_i915_gem_object *tmp, *next;
+
+	WARN_ON(!mutex_is_locked(&pool->dev->struct_mutex));
+
+	list_for_each_entry_safe(tmp, next,
+			&pool->cache_list, batch_pool_list) {
+
+		if (tmp->active)
+			continue;
+
+		/* While we're looping, do some clean up */
+		if (tmp->madv == __I915_MADV_PURGED) {
+			list_del(&tmp->batch_pool_list);
+			drm_gem_object_unreference(&tmp->base);
+			continue;
+		}
+
+		/*
+		 * Select a buffer that is at least as big as needed
+		 * but not 'too much' bigger. A better way to do this
+		 * might be to bucket the pool objects based on size.
+		 */
+		if (tmp->base.size >= size &&
+		    tmp->base.size <= (2 * size)) {
+			obj = tmp;
+			break;
+		}
+	}
+
+	if (!obj) {
+		obj = i915_gem_alloc_object(pool->dev, size);
+		if (!obj)
+			return ERR_PTR(-ENOMEM);
+
+		list_add_tail(&obj->batch_pool_list, &pool->cache_list);
+	}
+	else
+		/* Keep list in LRU order */
+		list_move_tail(&obj->batch_pool_list, &pool->cache_list);
+
+	return obj;
+}