[igt-dev] [PATCH] tests/kms_writeback.c: fix the `fill_fb` function

[Igor Matheus Andrade Torrente]

Currently, the `fill_fb` function, instead of filling the framebuffer
with the whole pixel, is only filling it with the rightmost byte.

This is happening because, even though the memset accepts an int as
a parameter, it's casting the value to unsigned char and will fill
the memory with this 8 bits value.

If we setup the pixel to 0xff0000|f0|, the buffer will filled with:

| addr     | = 0f
| addr + 1 | = 0f
| addr + 2 | = 0f
| addr + 3 | = 0f
    ...
| addr + N | = 0f

This patch address this issue by manually copying the entire integer
in the little-endian format.

Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente at gmail.com>
---
 tests/kms_writeback.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tests/kms_writeback.c b/tests/kms_writeback.c
index 60dbda2a..60d9b74e 100644
--- a/tests/kms_writeback.c
+++ b/tests/kms_writeback.c
@@ -227,14 +227,26 @@ static void writeback_fb_id(igt_output_t *output, igt_fb_t *valid_fb, igt_fb_t *
 
 static void fill_fb(igt_fb_t *fb, uint32_t pixel)
 {
-	void *ptr;
+	uint8_t *ptr, x, r, g, b, step = sizeof(uint32_t);
+	int64_t pixel_count, i;
 
 	igt_assert(fb->drm_format == DRM_FORMAT_XRGB8888);
 
 	ptr = igt_fb_map_buffer(fb->fd, fb);
 	igt_assert(ptr);
 
-	memset(ptr, pixel, fb->strides[0] * fb->height);
+	pixel_count = fb->strides[0] * fb->height;
+	x = (pixel & (0xff << 24)) >> 24;
+	r = (pixel & (0xff << 16)) >> 16;
+	g = (pixel & (0xff << 8)) >> 8;
+	b = pixel & 0xff;
+
+	for (i = 0; i <= pixel_count - step; i += step) {
+		ptr[i + 3] = x;
+		ptr[i + 2] = r;
+		ptr[i + 1] = g;
+		ptr[i + 0] = b;
+	}
 
 	igt_fb_unmap_buffer(fb, ptr);
 }
-- 
2.30.2