Re: [PATCH 2/7] drm/logicvc: Fix preferred fbdev cpp

From: Thomas Zimmermann <tzimmermann@suse.de>
To: Javier Martinez Canillas <javierm@redhat.com>,
	daniel@ffwll.ch, airlied@gmail.com, mripard@kernel.org,
	maarten.lankhorst@linux.intel.com, xinliang.liu@linaro.org,
	tiantao6@hisilicon.com, jstultz@google.com,
	kong.kongxinwei@hisilicon.com, puck.chen@hisilicon.com,
	paul.kocialkowski@bootlin.com, airlied@redhat.com,
	kraxel@redhat.com
Cc: dri-devel@lists.freedesktop.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 2/7] drm/logicvc: Fix preferred fbdev cpp
Date: Fri, 18 Nov 2022 14:48:17 +0100	[thread overview]
Message-ID: <2d2bf68d-6a6a-d00c-a277-4ebc492e8fae@suse.de> (raw)
In-Reply-To: <5893d46d-ca8a-81e4-2884-aa682ef69872@redhat.com>

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Hi

Am 18.11.22 um 14:41 schrieb Javier Martinez Canillas:
> On 11/18/22 14:22, Thomas Zimmermann wrote:
> 
> [...]
> 
>>>
>>> I'm also not sure if this is needed. Since IIUC in logicvc_mode_init() the
>>> driver does:
>>>
>>> 	preferred_depth = layer_primary->formats->depth;
>>>
>>> 	/* DRM counts alpha in depth, our driver doesn't. */
>>> 	if (layer_primary->formats->alpha)
>>> 		preferred_depth += 8;
>>>
>>> 	...
>>> 	mode_config->preferred_depth = preferred_depth;
>>>
>>> So it seems this patch is not needed? Unless I'm misunderstanding the code.
>>
>> The driver uses XRGB8888, so the 24-bit color depth has a 32-bit bpp
>> value. Hence the switch.
>>
> 
> Ah, I see. So is to set 32-bit bpp for both XRGB8888 and ARGB8888. But then
> I think that you also need to fix logicvc_mode_init() to remove that += 8?
> 
> Because right now the preferred_depth += 8 would set a preferred_depth of 32
> when should be just 24 even if alpha is enabled?
> 
> Or am I confusing again the meaning of the color depth?

For DRM, it's defined in drm_fourcc.c. ARGB8888 has a depth of 32 and 
XRGB8888 has a depth of 24. Both have a bpp of 32.

BUT in logicvc's internal data structure, both formats have a color 
depth of 24 and a bpp of 32.

Best regards
Thomas

> 

-- 
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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