docs/asahi: clarify twiddled vs GPU-tiled

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33743>

docs/drivers/asahi.rst

@@ -233,10 +233,10 @@ With these limitations, addressing into a strided linear image is as simple as
 
 In practice, this suffices for window system integration and little else.
 
-Twiddled
-````````
+GPU-tiled
+`````````
 
-The most common uncompressed layout is **twiddled**. The image is divided into
+The most common uncompressed layout is **GPU-tiled**. The image is divided into
 power-of-two sized tiles. The tiles themselves are stored in raster-order.
 Within each tile, elements (pixels/blocks) are stored in Morton (Z) order.
 
@@ -311,6 +311,23 @@ first layer, simplifying layout calculations for both software and hardware.
 Although the padding is logically unnecessary, it wastes little space compared
 to the sizes of large mipmapped 3D textures.
 
+Twiddled
+````````
+
+In addition to GPU-tiled images, AGX also has a fully **twiddled** layout. The
+image is rounded up to power-of-two dimensions, then all elements are stored in
+Morton (Z) order.
+
+A twiddled image is equivalent to a GPU-tiled image with a single square
+power-of-two tile spanning the entire image. That means GPU-tiled and twiddled
+images may share address calculation code, as long as everything is parametrized
+in terms of the tile size.
+
+In general, twiddled images require more memory than GPU-tiled images due to the
+extra padding required. Because GPU tiles are page-sized, twiddling beyond that
+does not offer any cache locality benefit either. The twiddled layout is
+mostly vestigial at this point, but the PBE requires it for sparse mapping.
+
 Sparse page tables
 ``````````````````