Re: [PATCH v4 1/6] drm/format-helper: Add drm_fb_xrgb8888_to_gray8_line()

Hello Andy,

On 2/11/22 11:28, Andy Shevchenko wrote:

On Fri, Feb 11, 2022 at 10:19:22AM +0100, Javier Martinez Canillas wrote:

quoted

Pull the per-line conversion logic into a separate helper function.

This will allow to do line-by-line conversion in other helpers that
convert to a gray8 format.

...

quoted

+static void drm_fb_xrgb8888_to_gray8_line(u8 *dst, const u32 *src, unsigned int pixels)
+{
+	unsigned int x;
+
+	for (x = 0; x < pixels; x++) {
+		u8 r = (*src & 0x00ff0000) >> 16;
+		u8 g = (*src & 0x0000ff00) >> 8;
+		u8 b =  *src & 0x000000ff;
+
+		/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
+		*dst++ = (3 * r + 6 * g + b) / 10;
+		src++;
+	}

Can be done as

	while (pixels--) {
		...
	}

or

	do {
		...
	} while (--pixels);

I don't see why a while loop would be an improvement here TBH.

In any case, I just pulled the line conversion logic as a separate
function with minimal code changes since doing that should be in a
separate patch.

Feel free to post a patch if you want to change that while loop.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat