linux-kernel - Re: [PATCH v4 1/6] drm/format-helper: Add drm_fb_xrgb8888_to_gray8

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Date:   Fri, 11 Feb 2022 13:12:57 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH v4 1/6] drm/format-helper: Add
 drm_fb_xrgb8888_to_gray8_line()

On Fri, Feb 11, 2022 at 11:40:13AM +0100, Javier Martinez Canillas wrote:
> On 2/11/22 11:28, Andy Shevchenko wrote:
> > On Fri, Feb 11, 2022 at 10:19:22AM +0100, Javier Martinez Canillas wrote:

...

> >> +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.

Less letters to parse when reading the code.

> 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.

Perhaps some day :-)

-- 
With Best Regards,
Andy Shevchenko