Quoting Liviu Dudau (2019-01-15 17:47:44)
> +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);
igt_memcpy_from_wc() for the reasons cited above.
-Chris
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