[Mesa-dev] [PATCH v3] panfrost: Rewrite u-interleaving code
Alyssa Rosenzweig
alyssa.rosenzweig at collabora.com
Fri Jun 28 22:06:32 UTC 2019
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 <alyssa.rosenzweig at collabora.com>
Reviewed-by: Vasily Khoruzhick <anarsoul at gmail.com>
Cc: Andreas Baierl <ichgeh at imkreisrum.de>
Cc: Erico Nunes <nunes.erico at gmail.com>
---
src/panfrost/shared/pan_tiling.c | 290 ++++++++++++++++++++-----------
1 file 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 <libv at skynet.be>
* Copyright (c) 2018 Alyssa Rosenzweig <alyssa at rosenzweig.io>
* Copyright (c) 2018 Vasily Khoruzhick <anarsoul at gmail.com>
+ * 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);
}
--
2.20.1
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