[Mesa-dev] [PATCH 2/6] i965: Fix comments about blit constraints

[Ben Widawsky]

The spec does say that the blitter is capable of transferring 64k scanlines in a
single blit operation. Perhaps this was true, or is still true on some
operations, but for all commands that we use, we are restricted to 16b signed:

For example, from the XY_SRC_COPY_CHROMA_BLT definition:
> Destination Y2 Coordinate (Bottom)
> 16 bit signed number.

v2: Rebase; conflicts resolved with wiggle

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
Reviewed-by: Neil Roberts <neil at linux.intel.com>
---
 src/mesa/drivers/dri/i965/intel_blit.c       | 8 ++++++--
 src/mesa/drivers/dri/i965/intel_copy_image.c | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/intel_blit.c b/src/mesa/drivers/dri/i965/intel_blit.c
index 6d92580..4a76ba9 100644
--- a/src/mesa/drivers/dri/i965/intel_blit.c
+++ b/src/mesa/drivers/dri/i965/intel_blit.c
@@ -298,11 +298,15 @@ intel_miptree_blit(struct brw_context *brw,
     *    The BLT engine is capable of transferring very large quantities of
     *    graphics data. Any graphics data read from and written to the
     *    destination is permitted to represent a number of pixels that
-    *    occupies up to 65,536 scan lines and up to 32,768 bytes per scan line
-    *    at the destination. The maximum number of pixels that may be
+    *    occupies up to 65,536 [sic] scan lines and up to 32,768 bytes per scan
+    *    line at the destination. The maximum number of pixels that may be
     *    represented per scan line’s worth of graphics data depends on the
     *    color depth.
     *
+    * XXX: The spec is likely incorrect. The number of scanlines is represented
+    * in the blit command as a 16b signed number, thus 32,767 as the max number
+    * of scanlines.
+    *
     * Furthermore, intelEmitCopyBlit (which is called below) uses a signed
     * 16-bit integer to represent buffer pitch, so it can only handle buffer
     * pitches < 32k. However, the pitch is measured in bytes for linear buffers
diff --git a/src/mesa/drivers/dri/i965/intel_copy_image.c b/src/mesa/drivers/dri/i965/intel_copy_image.c
index 3706704..c12decc 100644
--- a/src/mesa/drivers/dri/i965/intel_copy_image.c
+++ b/src/mesa/drivers/dri/i965/intel_copy_image.c
@@ -53,11 +53,15 @@ copy_image_with_blitter(struct brw_context *brw,
     *    The BLT engine is capable of transferring very large quantities of
     *    graphics data. Any graphics data read from and written to the
     *    destination is permitted to represent a number of pixels that
-    *    occupies up to 65,536 scan lines and up to 32,768 bytes per scan line
-    *    at the destination. The maximum number of pixels that may be
+    *    occupies up to 65,536 [sic] scan lines and up to 32,768 bytes per scan
+    *    line at the destination. The maximum number of pixels that may be
     *    represented per scan line’s worth of graphics data depends on the
     *    color depth.
     *
+    * XXX: The spec is likely incorrect. The number of scanlines is represented
+    * in the blit command as a 16b signed number, thus 32,767 as the max number
+    * of scanlines.
+    *
     * Furthermore, intelEmitCopyBlit (which is called below) uses a signed
     * 16-bit integer to represent buffer pitch, so it can only handle buffer
     * pitches < 32k.
-- 
2.5.0