[Intel-gfx] [PATCH i-g-t v5 3/6] lib: Add function to hash a framebuffer

Liviu Dudau
2019-01-15T17:47:44Z

From: Brian Starkey <brian.starkey@arm.com>

To use writeback buffers as a CRC source, we need to be able to hash
them. Implement a simple FVA-1a hashing routine for this purpose.

Doing a bytewise hash on the framebuffer directly can be very slow if
the memory is noncached. By making a copy of each line in the FB first
(which can take advantage of word-access speedup), we can do the hash
on a cached copy, which is much faster (10x speedup on my platform).

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
[rebased and updated to the most recent API]
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
---
lib/igt_fb.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++
lib/igt_fb.h | 3 +++
2 files changed, 69 insertions(+)

diff --git a/lib/igt_fb.c b/lib/igt_fb.c
index 5cd1829a3..11e200b53 100644
--- a/lib/igt_fb.c
+++ b/lib/igt_fb.c
@@ -2379,6 +2379,72 @@ bool igt_fb_supported_format(uint32_t drm_format)
return false;
}

+/*
+ * This implements the FNV-1a hashing algorithm instead of CRC, for
+ * simplicity
+ * http://www.isthe.com/chongo/tech/comp/fnv/index.html
+ *
+ * hash = offset_basis
+ * for each octet_of_data to be hashed
+ * hash = hash xor octet_of_data
+ * hash = hash * FNV_prime
+ * return hash
+ *
+ * 32 bit offset_basis = 2166136261
+ * 32 bit FNV_prime = 224 + 28 + 0x93 = 16777619
+ */
+int igt_fb_get_crc(struct igt_fb *fb, igt_crc_t *crc)
+{
+#define FNV1a_OFFSET_BIAS 2166136261
+#define FNV1a_PRIME 16777619
+ uint32_t hash;
+ void *map;
+ char *ptr, *line = NULL;
+ int x, y, cpp = igt_drm_format_to_bpp(fb->drm_format) / 8;
+ uint32_t stride = calc_plane_stride(fb, 0);
+
+ if (fb->is_dumb)
+ map = kmstest_dumb_map_buffer(fb->fd, fb->gem_handle, fb->size,
+ PROT_READ);
+ else
+ map = gem_mmap__gtt(fb->fd, fb->gem_handle, fb->size,
+ PROT_READ);
+ ptr = map;
+
+ /*
+ * Framebuffers are often uncached, which can make byte-wise accesses
+ * very slow. We copy each line of the FB into a local buffer to speed
+ * up the hashing.
+ */
+ line = malloc(stride);
+ if (!line) {
+ munmap(map, fb->size);
+ return -ENOMEM;
+ }
+
+ hash = FNV1a_OFFSET_BIAS;
+
+ for (y = 0; y < fb->height; y++, ptr += stride) {
+
+ memcpy(line, ptr, stride);
+
+ for (x = 0; x < fb->width * cpp; x++) {
+ hash ^= line[x];
+ hash *= FNV1a_PRIME;
+ }
+ }
+
+ crc->n_words = 1;
+ crc->crc[0] = hash;
+
+ free(line);
+ munmap(map, fb->size);
+
+ return 0;
+#undef FNV1a_OFFSET_BIAS
+#undef FNV1a_PRIME
+}
+
/**
* igt_format_is_yuv:
* @drm_format: drm fourcc
diff --git a/lib/igt_fb.h b/lib/igt_fb.h
index 9f027deba..948c5380c 100644
--- a/lib/igt_fb.h
+++ b/lib/igt_fb.h
@@ -37,6 +37,7 @@
#include <i915_drm.h>

#include "igt_color_encoding.h"
+#include "igt_debugfs.h"

/**
* igt_fb_t:
@@ -173,5 +174,7 @@ const char *igt_format_str(uint32_t drm_format);
bool igt_fb_supported_format(uint32_t drm_format);
bool igt_format_is_yuv(uint32_t drm_format);

+int igt_fb_get_crc(struct igt_fb *fb, igt_crc_t *crc);
+
#endif /* __IGT_FB_H__ */

--
2.20.1

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