On 11/04/2018 11:27, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-04-11 10:46:31)
+/**
+ * struct drm_i915_engine_info
+ *
+ * Describes one engine known to the driver, whether or not is physical engine
+ * only, or it can also be targetted from userspace, and what are its
+ * capabilities where applicable.
+ */
+struct drm_i915_engine_info {
+ /** Engine flags. */
+ __u64 flags;
+#define I915_ENGINE_FLAG_PHYSICAL (1 << 0)
+#define I915_ENGINE_FLAG_ABI (1 << 1)
+
+ /** Engine class as in enum drm_i915_gem_engine_class. */
+ __u16 class;
+
+ /** Engine instance number. */
+ __u16 instance;
+
+ __u32 rsvd0;
+
+ /** Capabilities of this engine. */
+ __u64 capabilities;
+#define I915_VCS_CLASS_CAPABILITY_HEVC (1 << 0)
+
+ __u64 rsvd1[2];
+};
+
+/**
+ * struct drm_i915_query_engine_info
+ *
+ * Engine info query enumerates all the engines known to the driver returning
+ * the array of struct drm_i915_engine_info structures.
+ */
+struct drm_i915_query_engine_info {
+ /** Number of struct drm_i915_engine_info structs following. */
+ __u32 num_engines;
+
+ /** MBZ */
+ __u32 rsvd[3];
Ok, I can understand having some reserved fields before the [], but
within struct drm_i915_engine_info isn't the size and layout determined
by flags? (Thinking about the tight protocol packing of the 80s and
slightly less tight packing for the 90s ;) Trade-off between ease of
decoder and running out of space?
How did that old saying go, was it "When in doubt, pad it out."? :)
But I think it is good to have some reserved fields rather than rely on
flags to extend the size of the structure. In any case I don't see a
significant downside to reserved fields.
Regards,
Tvrtko
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