panfrost: Rewrite u-interleaving code

Rather than using a magic lookup table with no explanations, let's add
liberal comments to the code to explain what this tiling scheme is and
how to encode/decode it efficiently.

It's not so mysterious after all -- just reordering bits with some XORs
thrown in.

v2: Correct copyright identifier. Fix spelling error. Switch space_4 to
a LUT. Fix comment typo. Use LUT instead of space_x tricks. Fallback on
generic rather than split up unaligned writes.

v3: Correct stride order (fixes crash loading). Correct coordinate
system mishap.

Signed-off-by: Alyssa Rosenzweig <[email protected]>
Reviewed-by: Vasily Khoruzhick <[email protected]>
Tested-by: Andreas Baierl <[email protected]>

1 files changed, 189 insertions, 101 deletions

diff --git a/src/panfrost/shared/pan_tiling.c b/src/panfrost/shared/pan_tiling.c
index 413cd89420b..08c9561b2ef 100644
--- a/src/panfrost/shared/pan_tiling.c
+++ b/src/panfrost/shared/pan_tiling.c
@@ -2,6 +2,7 @@
  * Copyright (c) 2011-2013 Luc Verhaegen <[email protected]>
  * Copyright (c) 2018 Alyssa Rosenzweig <[email protected]>
  * Copyright (c) 2018 Vasily Khoruzhick <[email protected]>
+ * Copyright (c) 2019 Collabora, Ltd.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -24,129 +25,212 @@
  *
  */
 
+#include <stdbool.h>
 #include "pan_tiling.h"
 
-uint32_t space_filler[16][16] = {
-   { 0,   1,   4,   5,   16,  17,  20,  21,  64,  65,  68,  69,  80,  81,  84,  85, },
-   { 3,   2,   7,   6,   19,  18,  23,  22,  67,  66,  71,  70,  83,  82,  87,  86, },
-   { 12,  13,  8,   9,   28,  29,  24,  25,  76,  77,  72,  73,  92,  93,  88,  89, },
-   { 15,  14,  11,  10,  31,  30,  27,  26,  79,  78,  75,  74,  95,  94,  91,  90, },
-   { 48,  49,  52,  53,  32,  33,  36,  37,  112, 113, 116, 117, 96,  97,  100, 101, },
-   { 51,  50,  55,  54,  35,  34,  39,  38,  115, 114, 119, 118, 99,  98,  103, 102, },
-   { 60,  61,  56,  57,  44,  45,  40,  41,  124, 125, 120, 121, 108, 109, 104, 105, },
-   { 63,  62,  59,  58,  47,  46,  43,  42,  127, 126, 123, 122, 111, 110, 107, 106, },
-   { 192, 193, 196, 197, 208, 209, 212, 213, 128, 129, 132, 133, 144, 145, 148, 149, },
-   { 195, 194, 199, 198, 211, 210, 215, 214, 131, 130, 135, 134, 147, 146, 151, 150, },
-   { 204, 205, 200, 201, 220, 221, 216, 217, 140, 141, 136, 137, 156, 157, 152, 153, },
-   { 207, 206, 203, 202, 223, 222, 219, 218, 143, 142, 139, 138, 159, 158, 155, 154, },
-   { 240, 241, 244, 245, 224, 225, 228, 229, 176, 177, 180, 181, 160, 161, 164, 165, },
-   { 243, 242, 247, 246, 227, 226, 231, 230, 179, 178, 183, 182, 163, 162, 167, 166, },
-   { 252, 253, 248, 249, 236, 237, 232, 233, 188, 189, 184, 185, 172, 173, 168, 169, },
-   { 255, 254, 251, 250, 239, 238, 235, 234, 191, 190, 187, 186, 175, 174, 171, 170, },
+/* This file implements software encode/decode of the tiling format used for
+ * textures and framebuffers primarily on Utgard GPUs. Names for this format
+ * include "Utgard-style tiling", "(Mali) swizzled textures", and
+ * "U-interleaved" (the former two names being used in the community
+ * Lima/Panfrost drivers; the latter name used internally at Arm).
+ * Conceptually, like any tiling scheme, the pixel reordering attempts to 2D
+ * spatial locality, to improve cache locality in both horizontal and vertical
+ * directions.
+ *
+ * This format is tiled: first, the image dimensions must be aligned to 16
+ * pixels in each axis. Once aligned, the image is divided into 16x16 tiles.
+ * This size harmonizes with other properties of the GPU; on Midgard,
+ * framebuffer tiles are logically 16x16 (this is the tile size used in
+ * Transaction Elimination and the minimum tile size used in Hierarchical
+ * Tiling). Conversely, for a standard 4 bytes-per-pixel format (like
+ * RGBA8888), 16 pixels * 4 bytes/pixel = 64 bytes, equal to the cache line
+ * size.
+ *
+ * Within each 16x16 block, the bits are reordered according to this pattern:
+ *
+ * | y3 | (x3 ^ y3) | y2 | (y2 ^ x2) | y1 | (y1 ^ x1) | y0 | (y0 ^ x0) |
+ *
+ * Basically, interleaving the X and Y bits, with XORs thrown in for every
+ * adjacent bit pair.
+ *
+ * This is cheap to implement both encode/decode in both hardware and software.
+ * In hardware, lines are simply rerouted to reorder and some XOR gates are
+ * thrown in. Software has to be a bit more clever.
+ *
+ * In software, the trick is to divide the pattern into two lines:
+ *
+ *    | y3 | y3 | y2 | y2 | y1 | y1 | y0 | y0 |
+ *  ^ |  0 | x3 |  0 | x2 |  0 | x1 |  0 | x0 |
+ *
+ * That is, duplicate the bits of the Y and space out the bits of the X. The
+ * top line is a function only of Y, so it can be calculated once per row and
+ * stored in a register. The bottom line is simply X with the bits spaced out.
+ * Spacing out the X is easy enough with a LUT, or by subtracting+ANDing the
+ * mask pattern (abusing carry bits).
+ *
+ * This format is also supported on Midgard GPUs, where it *can* be used for
+ * textures and framebuffers. That said, in practice it is usually as a
+ * fallback layout; Midgard introduces Arm FrameBuffer Compression, which is
+ * significantly more efficient than Utgard-style tiling and preferred for both
+ * textures and framebuffers, where possible. For unsupported texture types,
+ * for instance sRGB textures and framebuffers, this tiling scheme is used at a
+ * performance penalty, as AFBC is not compatible.
+ */
+
+/* Given the lower 4-bits of the Y coordinate, we would like to
+ * duplicate every bit over. So instead of 0b1010, we would like
+ * 0b11001100. The idea is that for the bits in the solely Y place, we
+ * get a Y place, and the bits in the XOR place *also* get a Y. */
+
+uint32_t bit_duplication[16] = {
+   0b00000000,
+   0b00000011,
+   0b00001100,
+   0b00001111,
+   0b00110000,
+   0b00110011,
+   0b00111100,
+   0b00111111,
+   0b11000000,
+   0b11000011,
+   0b11001100,
+   0b11001111,
+   0b11110000,
+   0b11110011,
+   0b11111100,
+   0b11111111,
+};
+
+/* Space the bits out of a 4-bit nibble */
+
+unsigned space_4[16] = {
+   0b0000000,
+   0b0000001,
+   0b0000100,
+   0b0000101,
+   0b0010000,
+   0b0010001,
+   0b0010100,
+   0b0010101,
+   0b1000000,
+   0b1000001,
+   0b1000100,
+   0b1000101,
+   0b1010000,
+   0b1010001,
+   0b1010100,
+   0b1010101
 };
 
+/* The scheme uses 16x16 tiles */
+
+#define TILE_WIDTH 16
+#define TILE_HEIGHT 16
+#define PIXELS_PER_TILE (TILE_WIDTH * TILE_HEIGHT)
+
+/* An optimized routine to tile an aligned (width & 0xF == 0) bpp4 texture */
+
 static void
 panfrost_store_tiled_image_bpp4(void *dst, const void *src,
                                const struct pipe_box *box,
                                uint32_t dst_stride,
                                uint32_t src_stride)
 {
+   /* Precompute the offset to the beginning of the first horizontal tile we're
+    * writing to, knowing that box->x is 16-aligned. Tiles themselves are
+    * stored linearly, so we get the X tile number by shifting and then
+    * multiply by the bytes per tile */
+
+   uint8_t *dest_start = dst + ((box->x >> 4) * PIXELS_PER_TILE * 4);
+
+   /* Iterate across the pixels we're trying to store in source-order */
+
    for (int y = box->y, src_y = 0; src_y < box->height; ++y, ++src_y) {
+      /* For each pixel in the destination image, figure out the part
+       * corresponding to the 16x16 block index */
+
       int block_y = y & ~0x0f;
-      int rem_y = y & 0x0F;
-      int block_start_s = block_y * dst_stride;
-      int source_start = src_y * src_stride;
 
-      for (int x = box->x, src_x = 0; src_x < box->width; ++x, ++src_x) {
-         int block_x_s = (x >> 4) * 256;
-         int rem_x = x & 0x0F;
+      /* In pixel coordinates (where the origin is the top-left), (block_y, 0)
+       * is the top-left corner of the leftmost tile in this row. While pixels
+       * are reordered within a block, the blocks themselves are stored
+       * linearly, so multiplying block_y by the pixel stride of the
+       * destination image equals the byte offset of that top-left corner of
+       * the block this row is in */
+
+      uint32_t *dest = (uint32_t *) (dest_start + (block_y * dst_stride));
+
+      /* The source is actually linear, so compute the byte offset to the start
+       * and end of this row in the source */
+
+      const uint32_t *source = src + (src_y * src_stride);
+      const uint32_t *source_end = source + box->width;
+
+      /* We want to duplicate the bits of the bottom nibble of Y */
+      unsigned expanded_y = bit_duplication[y & 0xF];
 
-         int index = space_filler[rem_y][rem_x];
-         const uint32_t *source = src + source_start + 4 * src_x;
-         uint32_t *dest = dst + block_start_s + 4 * (block_x_s + index);
+      /* Iterate the row in source order. In the outer loop, we iterate 16
+       * bytes tiles. After each tile, we increment dest to include the size of
+       * that tile in pixels. */
 
-         *dest = *source;
+      for (; source < source_end; dest += PIXELS_PER_TILE) {
+         /* Within each tile, we iterate each of the 16 pixels in the row of
+          * the tile. This loop should be unrolled. */
+
+         for (int i = 0; i < 16; ++i) {
+            /* We have the X component spaced out in space_x and we have the Y
+             * component duplicated. So we just XOR them together. The X bits
+             * get the XOR like the pattern needs. The Y bits are XORing with
+             * zero so this is a no-op */
+
+            unsigned index = expanded_y ^ space_4[i];
+
+            /* Copy over the pixel */
+            dest[index] = *(source++);
+         }
       }
    }
 }
 
 static void
-panfrost_store_tiled_image_generic(void *dst, const void *src,
+panfrost_access_tiled_image_generic(void *dst, void *src,
                                const struct pipe_box *box,
                                uint32_t dst_stride,
                                uint32_t src_stride,
-                               uint32_t bpp)
+                               uint32_t bpp,
+                               bool is_store)
 {
    for (int y = box->y, src_y = 0; src_y < box->height; ++y, ++src_y) {
       int block_y = y & ~0x0f;
-      int rem_y = y & 0x0F;
       int block_start_s = block_y * dst_stride;
       int source_start = src_y * src_stride;
 
-      for (int x = box->x, src_x = 0; src_x < box->width; ++x, ++src_x) {
-         int block_x_s = (x >> 4) * 256;
-         int rem_x = x & 0x0F;
-
-         int index = space_filler[rem_y][rem_x];
-         const uint8_t *src8 = src;
-         const uint8_t *source = &src8[source_start + bpp * src_x];
-         uint8_t *dest = dst + block_start_s + bpp * (block_x_s + index);
-
-         for (int b = 0; b < bpp; ++b)
-            dest[b] = source[b];
-      }
-   }
-}
-
-static void
-panfrost_load_tiled_image_bpp4(void *dst, const void *src,
-                              const struct pipe_box *box,
-                              uint32_t dst_stride,
-                              uint32_t src_stride)
-{
-   for (int y = box->y, dest_y = 0; dest_y < box->height; ++y, ++dest_y) {
-      int block_y = y & ~0x0f;
-      int rem_y = y & 0x0F;
-      int block_start_s = block_y * src_stride;
-      int dest_start = dest_y * dst_stride;
+      unsigned expanded_y = bit_duplication[y & 0xF];
 
-      for (int x = box->x, dest_x = 0; dest_x < box->width; ++x, ++dest_x) {
+      for (int x = box->x, src_x = 0; src_x < box->width; ++x, ++src_x) {
          int block_x_s = (x >> 4) * 256;
-         int rem_x = x & 0x0F;
-
-         int index = space_filler[rem_y][rem_x];
-         uint32_t *dest = dst + dest_start + 4 * dest_x;
-         const uint32_t *source = src + block_start_s + 4 * (block_x_s + index);
 
-         *dest = *source;
-      }
-   }
-}
+         unsigned index = expanded_y ^ space_4[x & 0xF];
 
-static void
-panfrost_load_tiled_image_generic(void *dst, const void *src,
-                              const struct pipe_box *box,
-                              uint32_t dst_stride,
-                              uint32_t src_stride,
-                              uint32_t bpp)
-{
-   for (int y = box->y, dest_y = 0; dest_y < box->height; ++y, ++dest_y) {
-      int block_y = y & ~0x0f;
-      int rem_y = y & 0x0F;
-      int block_start_s = block_y * src_stride;
-      int dest_start = dest_y * dst_stride;
+         uint8_t *src8 = src;
+         uint8_t *source = &src8[source_start + bpp * src_x];
+         uint8_t *dest = dst + block_start_s + bpp * (block_x_s + index);
 
-      for (int x = box->x, dest_x = 0; dest_x < box->width; ++x, ++dest_x) {
-         int block_x_s = (x >> 4) * 256;
-         int rem_x = x & 0x0F;
+         uint8_t *out = is_store ? dest : source;
+         uint8_t *in = is_store ? source : dest;
 
-         int index = space_filler[rem_y][rem_x];
-         uint8_t *dst8 = dst;
-         uint8_t *dest = &dst8[dest_start + bpp * dest_x];
-         const uint8_t *source = src + block_start_s + bpp * (block_x_s + index);
+         /* Write out 1-4 bytes. Written like this rather than a loop so the
+          * compiler doesn't need to do branching (just some predication) */
 
-         for (int b = 0; b < bpp; ++b)
-            dest[b] = source[b];
+         out[0] = in[0];
+         if (bpp > 1) {
+            out[1] = in[1];
+            if (bpp > 2) {
+               out[2] = in[2];
+               if (bpp > 3)
+                  out[3] = in[3];
+            }
+         }
       }
    }
 }
@@ -158,13 +242,23 @@ panfrost_store_tiled_image(void *dst, const void *src,
                            uint32_t src_stride,
                            uint32_t bpp)
 {
-	switch (bpp) {
-	case 4:
-		panfrost_store_tiled_image_bpp4(dst, src, box, dst_stride, src_stride);
-		break;
-	default:
-		panfrost_store_tiled_image_generic(dst, src, box, dst_stride, src_stride, bpp);
-	}
+   /* The optimized path is for aligned writes specifically */
+
+   if (box->x & 0xF || box->width & 0xF) {
+      panfrost_access_tiled_image_generic(dst, (void *) src, box, dst_stride, src_stride, bpp, TRUE);
+      return;
+   }
+
+   /* Attempt to use an optimized path if we have one */
+
+   switch (bpp) {
+      case 4:
+         panfrost_store_tiled_image_bpp4(dst, (void *) src, box, dst_stride, src_stride);
+         break;
+      default:
+         panfrost_access_tiled_image_generic(dst, (void *) src, box, dst_stride, src_stride, bpp, TRUE);
+         break;
+   }
 }
 
 void
@@ -174,11 +268,5 @@ panfrost_load_tiled_image(void *dst, const void *src,
                            uint32_t src_stride,
                            uint32_t bpp)
 {
-	switch (bpp) {
-	case 4:
-		panfrost_load_tiled_image_bpp4(dst, src, box, dst_stride, src_stride);
-		break;
-	default:
-		panfrost_load_tiled_image_generic(dst, src, box, dst_stride, src_stride, bpp);
-	}
+   panfrost_access_tiled_image_generic((void *) src, dst, box, src_stride, dst_stride, bpp, FALSE);
 }