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

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Message-ID: <7560cd10-0a7c-3fda-da83-9008833e3901@suse.de>
Date:   Fri, 11 Feb 2022 12:54:26 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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, 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()

Hi

Am 11.02.22 um 12:12 schrieb Andy Shevchenko:
> 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.

It's a simple refactoring of code that has worked well so far. Let's 
leave it as-is for now.

Best regards
Thomas

> 
>> 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 :-)
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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