Mesa (master): intel: Fix ReadPixels on buffers whose width >= 32kbytes

[Paul Berry]

Module: Mesa
Branch: master
Commit: b50c0feb2ccf3a4e1be8133405347ee3b49b05cf
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=b50c0feb2ccf3a4e1be8133405347ee3b49b05cf

Author: Paul Berry <stereotype441 at gmail.com>
Date:   Thu Jan 24 10:43:38 2013 -0800

intel: Fix ReadPixels on buffers whose width >= 32kbytes

When possible, glReadPixels calls are performed using the hardware
blitter.  However, according to the Ivy Bridge PRM, Vol1 Part4,
section 1.2.1.2 (Graphics Data Size Limitations):

    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
    represented per scan line’s worth of graphics data depends on the
    color depth.

With an RGBA32F color buffer (which has 16 bytes per pixel) this
imposes a maximum width of 2048 pixels.

To make matters worse, if the pitch of the buffer is 32k or greater,
intel_miptree_map_blit's call to intelEmitCopyBlit will overflow
intelEmitCopyBlit's src_pitch and dst_pitch parameters (which are
16-bit signed integers).

We can conveniently avoid both problems by avoiding the readpixels
blit path when the miptree's pitch is >= 32k.

Fixes gles3conform "half_float" tests when the buffer width is greater
than 2048.

Reviewed-by: Eric Anholt <eric at anholt.net>
Tested-by: Ian Romanick <ian.d.romanick at intel.com>

---

 src/mesa/drivers/dri/intel/intel_mipmap_tree.c |   28 ++++++++++++++++++++---
 1 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/intel/intel_mipmap_tree.c b/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
index ce03afa..a063f87 100644
--- a/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
+++ b/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
@@ -1565,10 +1565,30 @@ intel_miptree_map_singlesample(struct intel_context *intel,
       intel_miptree_map_etc(intel, mt, map, level, slice);
    } else if (mt->stencil_mt) {
       intel_miptree_map_depthstencil(intel, mt, map, level, slice);
-   } else if (intel->has_llc &&
-	      !(mode & GL_MAP_WRITE_BIT) &&
-	      !mt->compressed &&
-	      mt->region->tiling == I915_TILING_X) {
+   }
+   /* According to the Ivy Bridge PRM, Vol1 Part4, section 1.2.1.2 (Graphics
+    * Data Size Limitations):
+    *
+    *    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
+    *    represented per scan line’s worth of graphics data depends on the
+    *    color depth.
+    *
+    * Furthermore, intelEmitCopyBlit (which is called by
+    * intel_miptree_map_blit) uses a signed 16-bit integer to represent buffer
+    * pitch, so it can only handle buffer pitches < 32k.
+    *
+    * As a result of these two limitations, we can only use
+    * intel_miptree_map_blit() when the region's pitsh is less than 32k.
+    */
+   else if (intel->has_llc &&
+            !(mode & GL_MAP_WRITE_BIT) &&
+            !mt->compressed &&
+            mt->region->tiling == I915_TILING_X &&
+            mt->region->pitch < 32768) {
       intel_miptree_map_blit(intel, mt, map, level, slice);
    } else {
       intel_miptree_map_gtt(intel, mt, map, level, slice);