ail: Add get_wsi_stride_B helper

Centralize the logic around WSI strides, which are a software convention made
into UAPI rather than something set in silicon.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19606>

src/asahi/layout/layout.h

@@ -116,6 +116,25 @@ ail_get_linear_stride_B(struct ail_layout *layout, ASSERTED uint8_t level)
    return layout->linear_stride_B;
 }
 
+/*
+ * For WSI purposes, we need to associate a stride with all layouts. In the
+ * hardware, only strided linear images have an associated stride, there is no
+ * natural stride associated with twiddled images. However, various clients
+ * assert that the stride is valid for the image if it were linear (even if it
+ * is in fact not linear). In those cases, by convention we use the minimum
+ * valid such stride.
+ */
+static inline uint32_t
+ail_get_wsi_stride_B(struct ail_layout *layout, unsigned level)
+{
+   assert(level == 0 && "Mipmaps cannot be shared as WSI");
+
+   if (layout->tiling == AIL_TILING_LINEAR)
+      return ail_get_linear_stride_B(layout, level);
+   else
+      return util_format_get_stride(layout->format, layout->width_px);
+}
+
 static inline uint32_t
 ail_get_layer_offset_B(struct ail_layout *layout, unsigned z_px)
 {