From: Brian Starkey <brian.star...@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.star...@arm.com>
---
lib/igt_fb.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
lib/igt_fb.h | 5 +++++
2 files changed, 70 insertions(+)
diff --git a/lib/igt_fb.c b/lib/igt_fb.c
index d2b7e9e3..f613bb2e 100644
--- a/lib/igt_fb.c
+++ b/lib/igt_fb.c
@@ -1302,3 +1302,68 @@ void igt_get_all_cairo_formats(const uint32_t **formats,
int *format_count)
*formats = drm_formats;
*format_count = n_formats;
}
+
+/*
+ * 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;
+
+ 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(fb->stride);
+ if (!line) {
+ munmap(map, fb->size);
+ return -ENOMEM;
+ }
+
+ hash = FNV1a_OFFSET_BIAS;
+
+ for (y = 0; y < fb->height; y++, ptr += fb->stride) {
+
+ memcpy(line, ptr, fb->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
+}
diff --git a/lib/igt_fb.h b/lib/igt_fb.h
index 4a680cef..04430e9d 100644
--- a/lib/igt_fb.h
+++ b/lib/igt_fb.h
@@ -43,6 +43,8 @@ typedef struct _cairo cairo_t;
#include <i915_drm.h>
+#include "igt_crc.h"
+
/**
* igt_fb_t:
* @fb_id: KMS ID of the framebuffer
@@ -156,5 +158,8 @@ uint32_t igt_drm_format_to_bpp(uint32_t drm_format);
const char *igt_format_str(uint32_t drm_format);
void igt_get_all_cairo_formats(const uint32_t **formats, int *format_count);
+/* Get a hash for a framebuffer */
+int igt_fb_get_crc(struct igt_fb *fb, igt_crc_t *crc);
+
#endif /* __IGT_FB_H__ */
--
2.13.2
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