isl: Drop misplaced comment about padding

isl has a giant comment that explains the hardware's padding
requirements. (Hint: Cache lines and page faults). But the comment is in
the wrong place, in isl_calc_linear_row_pitch(), which is unrelated to
padding.

The important parts of that comment were copied to
isl_apply_surface_padding() long ago. So drop the misplaced comment.

Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/intel/isl/isl.c b/src/intel/isl/isl.c
index b4bdf2059ac53b1e074ccbc9084baaf596d0bb13..515d2c3fa31e1818e66658051039d44a4c921141 100644 (file)
--- a/src/intel/isl/isl.c
+++ b/src/intel/isl/isl.c
@@ -1004,53 +1004,7 @@ isl_calc_linear_row_pitch(const struct isl_device *dev,
                           const struct isl_extent2d *phys_slice0_sa)
 {
    const struct isl_format_layout *fmtl = isl_format_get_layout(info->format);
-
    uint32_t row_pitch = info->min_pitch;
-
-   /* First, align the surface to a cache line boundary, as the PRM explains
-    * below.
-    *
-    * From the Broadwell PRM >> Volume 5: Memory Views >> Common Surface
-    * Formats >> Surface Padding Requirements >> Render Target and Media
-    * Surfaces:
-    *
-    *    The data port accesses data (pixels) outside of the surface if they
-    *    are contained in the same cache request as pixels that are within the
-    *    surface. These pixels will not be returned by the requesting message,
-    *    however if these pixels lie outside of defined pages in the GTT,
-    *    a GTT error will result when the cache request is processed. In order
-    *    to avoid these GTT errors, “padding” at the bottom of the surface is
-    *    sometimes necessary.
-    *
-    * From the Broadwell PRM >> Volume 5: Memory Views >> Common Surface
-    * Formats >> Surface Padding Requirements >> Sampling Engine Surfaces:
-    *
-    *    The sampling engine accesses texels outside of the surface if they
-    *    are contained in the same cache line as texels that are within the
-    *    surface.  These texels will not participate in any calculation
-    *    performed by the sampling engine and will not affect the result of
-    *    any sampling engine operation, however if these texels lie outside of
-    *    defined pages in the GTT, a GTT error will result when the cache line
-    *    is accessed. In order to avoid these GTT errors, “padding” at the
-    *    bottom and right side of a sampling engine surface is sometimes
-    *    necessary.
-    *
-    *    It is possible that a cache line will straddle a page boundary if the
-    *    base address or pitch is not aligned. All pages included in the cache
-    *    lines that are part of the surface must map to valid GTT entries to
-    *    avoid errors. To determine the necessary padding on the bottom and
-    *    right side of the surface, refer to the table in  Alignment Unit Size
-    *    section for the i and j parameters for the surface format in use. The
-    *    surface must then be extended to the next multiple of the alignment
-    *    unit size in each dimension, and all texels contained in this
-    *    extended surface must have valid GTT entries.
-    *
-    *    For example, suppose the surface size is 15 texels by 10 texels and
-    *    the alignment parameters are i=4 and j=2. In this case, the extended
-    *    surface would be 16 by 10. Note that these calculations are done in
-    *    texels, and must be converted to bytes based on the surface format
-    *    being used to determine whether additional pages need to be defined.
-    */
    assert(phys_slice0_sa->w % fmtl->bw == 0);
    const uint32_t bs = fmtl->bpb / 8;
    row_pitch = MAX(row_pitch, bs * (phys_slice0_sa->w / fmtl->bw));