Re: [PATCH 3/6] drm/vc4: txp: Force alpha to be 0xff if it's disabled

From: Thomas Zimmermann <tzimmermann@suse.de>
To: Maxime Ripard <maxime@cerno.tech>, dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>, Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 3/6] drm/vc4: txp: Force alpha to be 0xff if it's disabled
Date: Wed, 6 Apr 2022 11:02:43 +0200	[thread overview]
Message-ID: <8cba63bd-9572-caf5-de85-8d60be7bab26@suse.de> (raw)
In-Reply-To: <20220328153659.2382206-4-maxime@cerno.tech>

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Hi Maxime

Am 28.03.22 um 17:36 schrieb Maxime Ripard:
> If we use a format that has padding instead of the alpha component (such
> as XRGB8888), it appears that the Transposer will fill the padding to 0,
> disregarding what was stored in the input buffer padding.
> 
> This leads to issues with IGT, since it will set the padding to 0xff,
> but will then compare the CRC of the two frames which will thus fail.
> Another nice side effect is that it is now possible to just use the
> buffer as ARGB.
> 
> Fixes: 008095e065a8 ("drm/vc4: Add support for the transposer block")
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>   drivers/gpu/drm/vc4/vc4_txp.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_txp.c b/drivers/gpu/drm/vc4/vc4_txp.c
> index ace2d03649ba..5b4dd644214f 100644
> --- a/drivers/gpu/drm/vc4/vc4_txp.c
> +++ b/drivers/gpu/drm/vc4/vc4_txp.c
> @@ -304,6 +304,8 @@ static void vc4_txp_connector_atomic_commit(struct drm_connector *conn,
>   
>   	if (fb->format->has_alpha)
>   		ctrl |= TXP_ALPHA_ENABLE;
> +	else
> +		ctrl |= TXP_ALPHA_INVERT;

'Invert' is somewhat misleading here, but your commit message nicely 
explains what this code does. Maybe add a short comment with the 
explanation.

Best regards
Thomas

>   
>   	gem = drm_fb_cma_get_gem_obj(fb, 0);
>   	TXP_WRITE(TXP_DST_PTR, gem->paddr + fb->offsets[0]);

-- 
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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