[Intel-gfx] [PATCH v7 05/15] drm/i915/ttm: Embed a ttm buffer object in the i915 gem object

Thomas Hellström
2021-05-31T12:20:21Z

Embed a struct ttm_buffer_object into the i915 gem object, making sure
we alias the gem object part. It's a bit unfortunate that the
struct ttm_buffer_ojbect embeds a gem object since we otherwise could
make the TTM part private to the TTM backend, and use the usual
i915 gem object for the other backends.
To make this a bit more storage efficient for the other backends,
we'd have to use a pointer for the gem object which would require
a lot of changes in the driver. We postpone that for later.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
drivers/gpu/drm/i915/gem/i915_gem_object.c | 7 +++++++
drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 12 +++++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 2be6109d0093..5706d471692d 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -62,6 +62,13 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
const struct drm_i915_gem_object_ops *ops,
struct lock_class_key *key, unsigned flags)
{
+ /*
+ * A gem object is embedded both in a struct ttm_buffer_object :/ and
+ * in a drm_i915_gem_object. Make sure they are aliased.
+ */
+ BUILD_BUG_ON(offsetof(typeof(*obj), base) !=
+ offsetof(typeof(*obj), __do_not_access.base));
+
spin_lock_init(&obj->vma.lock);
INIT_LIST_HEAD(&obj->vma.list);

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
index f5b46d11e6e6..d047ea126029 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -10,6 +10,7 @@
#include <linux/mmu_notifier.h>

#include <drm/drm_gem.h>
+#include <drm/ttm/ttm_bo_api.h>
#include <uapi/drm/i915_drm.h>

#include "i915_active.h"
@@ -99,7 +100,16 @@ struct i915_gem_object_page_iter {
};

struct drm_i915_gem_object {
- struct drm_gem_object base;
+ /*
+ * We might have reason to revisit the below since it wastes
+ * a lot of space for non-ttm gem objects.
+ * In any case, always use the accessors for the ttm_buffer_object
+ * when accessing it.
+ */
+ union {
+ struct drm_gem_object base;
+ struct ttm_buffer_object __do_not_access;
+ };

const struct drm_i915_gem_object_ops *ops;