[Intel-xe] [RFC PATCH] drm/xe/uAPi: Clarify the meaning of min_page_size and MIN_ALIGNMENT

[Thomas Hellström]

In particular, don't *enforce* alignment of buffer object sizes to
MIN_ALIGNMENT, as enforcing that for imported dma-bufs would not
really make sense.

Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: Francois Dugast <francois.dugast at intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 include/uapi/drm/xe_drm.h | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
index d48d8e3c898c..5895c95879d1 100644
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -167,11 +167,10 @@ struct drm_xe_query_mem_region {
 	 *
 	 * When the kernel allocates memory for this region, the
 	 * underlying pages will be at least @min_page_size in size.
-	 *
-	 * Important note: When userspace allocates a GTT address which
-	 * can point to memory allocated from this region, it must also
-	 * respect this minimum alignment. This is enforced by the
-	 * kernel.
+	 * Buffer objects with an allowable placement in this region may
+	 * be created with a smaller size, but for increased performance,
+	 * user-space drivers should align sizes of such buffer objects
+	 * to this value whenever possible.
 	 */
 	__u32 min_page_size;
 	/**
@@ -252,6 +251,14 @@ struct drm_xe_query_config {
 #define XE_QUERY_CONFIG_REV_AND_DEVICE_ID	0
 #define XE_QUERY_CONFIG_FLAGS			1
 	#define XE_QUERY_CONFIG_FLAGS_HAS_VRAM		(0x1 << 0)
+/*
+ * XE_QUERY_CONFIG_MIN_ALIGNMENT - GPU VM bind address - and size alignment.
+ * GPU virtual address mappings of buffer objects must have their VM addr and
+ * range aligned to this value, with the exception of buffer objects with
+ * allowable placement in system memory only. If this alignment results in
+ * a mapping beyond the end of the buffer object, accesses beyond the
+ * end of the buffer object have undefined reslut.
+ */
 #define XE_QUERY_CONFIG_MIN_ALIGNMENT		2
 #define XE_QUERY_CONFIG_VA_BITS			3
 #define XE_QUERY_CONFIG_GT_COUNT		4
-- 
2.41.0