gallium/util: Add pixel->blocks box helper

There is a lot of unit confusion in Gallium due to pixels versus blocks
matching only with uncompressed textures. Add a helper to do a common
pixels->blocks unit conversion required in multiple drivers.

v2: Rename dst->blocks, src->pixels to avoid confusion about the units
to casual readers (Mike).

Note to mesa-stable maintainers: this is marked as Cc: mesa-stable so
the next patch (a set of bug fixes for Lima and Panfrost) can be
backported. It's not a bug fix in its own right, of course.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net> [v1]
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14370>
(cherry picked from commit 26c533f167)

.pick_status.json

@@ -805,7 +805,7 @@
         "description": "gallium/util: Add pixel->blocks box helper",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/gallium/auxiliary/util/u_box.h

@@ -3,6 +3,7 @@
 
 #include "pipe/p_state.h"
 #include "util/u_math.h"
+#include "util/format/u_format.h"
 
 static inline void
 u_box_1d(unsigned x, unsigned w, struct pipe_box *box)
@@ -239,4 +240,22 @@ u_box_minify_3d(struct pipe_box *dst,
    dst->depth = MAX2(src->depth >> l, 1);
 }
 
+/* Converts a box specified in pixels to an equivalent box specified
+ * in blocks, where the boxes represent a region-of-interest of an image with
+ * the given format. This is trivial (a copy) for uncompressed formats.
+ */
+static inline void
+u_box_pixels_to_blocks(struct pipe_box *blocks,
+                       const struct pipe_box *pixels, enum pipe_format format)
+{
+   u_box_3d(
+         pixels->x / util_format_get_blockwidth(format),
+         pixels->y / util_format_get_blockheight(format),
+         pixels->z,
+         DIV_ROUND_UP(pixels->width, util_format_get_blockwidth(format)),
+         DIV_ROUND_UP(pixels->height, util_format_get_blockheight(format)),
+         pixels->depth,
+         blocks);
+}
+
 #endif