[Intel-xe] [PATCH] drm/xe/hw_engine: Document difference between instance and logical instance

[Francois Dugast]

Add explanation provided by Matt next to the definition, so that
it can easily found later.

Signed-off-by: Francois Dugast <francois.dugast at intel.com>
---
 drivers/gpu/drm/xe/xe_hw_engine_types.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_hw_engine_types.h b/drivers/gpu/drm/xe/xe_hw_engine_types.h
index 5d4ee2904240..aa8b5a2165c5 100644
--- a/drivers/gpu/drm/xe/xe_hw_engine_types.h
+++ b/drivers/gpu/drm/xe/xe_hw_engine_types.h
@@ -114,7 +114,13 @@ struct xe_hw_engine {
 	enum xe_engine_class class;
 	/** @instance: physical instance of this hw engine */
 	u16 instance;
-	/** @logical_instance: logical instance of this hw engine */
+	/**
+	 * @logical_instance: logical instance of this hw engine. This is
+	 * different from @instance because there can be gaps in physical
+	 * engines. For example on TGL VCS0 and CVS2 map to logical
+	 * instances 0 and 1. Only logical instances should be exposed to
+	 * user space.
+	 */
 	u16 logical_instance;
 	/** @mmio_base: MMIO base address of this hw engine*/
 	u32 mmio_base;
-- 
2.34.1