Re: [PATCH v7 1/9] drm/format-helper: Add drm_fb_blit_from_r1 and drm_fb_fill

From: Thomas Zimmermann <tzimmermann@suse.de>
To: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Jocelyn Falempe <jfalempe@redhat.com>,
	bluescreen_avenger@verizon.net, javierm@redhat.com,
	mripard@kernel.org, gpiccoli@igalia.com, noralf@tronnes.org,
	dri-devel@lists.freedesktop.org, daniel@ffwll.ch,
	airlied@redhat.com
Subject: Re: [PATCH v7 1/9] drm/format-helper: Add drm_fb_blit_from_r1 and drm_fb_fill
Date: Fri, 19 Jan 2024 14:31:34 +0100	[thread overview]
Message-ID: <026a00b2-6677-4bfb-8ee8-1678080b43a6@suse.de> (raw)
In-Reply-To: <20240119142536.5023860b@eldfell>

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Hi

Am 19.01.24 um 13:25 schrieb Pekka Paalanen:
> On Fri, 19 Jan 2024 11:58:38 +0100
> Thomas Zimmermann <tzimmermann@suse.de> wrote:
> 
>> Hi
>>
>> Am 17.01.24 um 17:40 schrieb Jocelyn Falempe:
> 
> ...
> 
>>> The last thing, is if I plan to add YUV support, with this
>>> implementation, I only need to write one function that convert one
>>> pixel. Otherwise I would need to add the drm_fb_r1_to_yuvxxx_line() and
>>> drm_fb_r1_to_yuvxxxx() boilerplate.
>>
>> 8) YUVs are multi-plane formats IIRC. So it's likely a bit more
>> complicated.And I'm not aware of any current use case for YUV. If the
>> framebuffer console doesn't support it, the panic helper probably won't
>> either.
> 
> Kernel panic during a fullscreen video playback, maybe?
> 
> That use case is likely to have an YUV FB as the only visible KMS plane
> FB, either primary or overlay plane depending on which is capable of
> displaying it. Sub-titles might not exist, or might be in a fairly
> small RGB overlay.
> 
> I don't know if such case is important enough to handle.

That's at least a possible use case AFAICT.

Each conversion is implemented in a helper drm_fb_<src format>_to_<dst 
format>(). drm_fb_blit() is just a big switch statement to call the 
correct helper. Something like drm_r1_to_yuv422() would be no different 
and would integrate with the existing drm_fb_blit() nicely.

So it appears to me as if it's better to either extend the current code 
for multi-plane formats, or write custom helpers 
drm_fb_r1_to_yuv<whatever>().

Best regards
Thomas

> 
> 
> Thanks,
> pq

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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