iris: Use a larger alignment for buffer allocations

This is likely required for OpenGL buffer texture allocations.  It'll
also make buffer copies faster if things are generally nicely aligned.
It's definitely required for OpenCL.

Fixes: 32c5d6d1dc ("iris: Add an alignment parameter to iris_bo_alloc()")
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15811>
(cherry picked from commit 2984134395)

.pick_status.json

@@ -2083,7 +2083,7 @@
         "description": "iris: Use a larger alignment for buffer allocations",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "32c5d6d1dca2094351911fa7ca6c5c3eb532581d"
     },

src/gallium/drivers/iris/iris_resource.c

@@ -1076,6 +1076,22 @@ iris_resource_finish_aux_import(struct pipe_screen *pscreen,
    }
 }
 
+static uint32_t
+iris_buffer_alignment(uint64_t size)
+{
+   /* Some buffer operations want some amount of alignment.  The largest
+    * buffer texture pixel size is 4 * 4 = 16B.  OpenCL data is also supposed
+    * to be aligned and largest OpenCL data type is a double16 which is
+    * 8 * 16 = 128B.  Align to the largest power of 2 which fits in the size,
+    * up to 128B.
+    */
+   uint32_t align = MAX2(4 * 4, 8 * 16);
+   while (align > size)
+      align >>= 1;
+
+   return align;
+}
+
 static struct pipe_resource *
 iris_resource_create_for_buffer(struct pipe_screen *pscreen,
                                 const struct pipe_resource *templ)
@@ -1110,8 +1126,9 @@ iris_resource_create_for_buffer(struct pipe_screen *pscreen,
 
    unsigned flags = iris_resource_alloc_flags(screen, templ, res->aux.usage);
 
-   res->bo =
-      iris_bo_alloc(screen->bufmgr, name, templ->width0, 1, memzone, flags);
+   res->bo = iris_bo_alloc(screen->bufmgr, name, templ->width0,
+                           iris_buffer_alignment(templ->width0),
+                           memzone, flags);
 
    if (!res->bo) {
       iris_resource_destroy(pscreen, &res->base.b);
@@ -1913,7 +1930,8 @@ iris_invalidate_resource(struct pipe_context *ctx,
 
    struct iris_bo *old_bo = res->bo;
    struct iris_bo *new_bo =
-      iris_bo_alloc(screen->bufmgr, res->bo->name, resource->width0, 1,
+      iris_bo_alloc(screen->bufmgr, res->bo->name, resource->width0,
+                    iris_buffer_alignment(resource->width0),
                     iris_memzone_for_address(old_bo->address), 0);
    if (!new_bo)
       return;