Re: [PATCH 4/6] drm/format-helper: Support the AB24 format

From: Thomas Zimmermann <tzimmermann@suse.de>
To: Thierry Reding <thierry.reding@gmail.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc: linux-tegra@vger.kernel.org, devicetree@vger.kernel.org,
	dri-devel@lists.freedesktop.org,
	Jon Hunter <jonathanh@nvidia.com>
Subject: Re: [PATCH 4/6] drm/format-helper: Support the AB24 format
Date: Wed, 7 Sep 2022 09:23:01 +0200	[thread overview]
Message-ID: <d4e76fbc-bb75-4b1a-c345-5dc7670d6a14@suse.de> (raw)
In-Reply-To: <20220905163300.391692-5-thierry.reding@gmail.com>

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Hi

Am 05.09.22 um 18:32 schrieb Thierry Reding:
> From: Thierry Reding <treding@nvidia.com>
> 
> Add a conversion helper for the AB24 format to use in drm_fb_blit().
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>   drivers/gpu/drm/drm_format_helper.c | 35 +++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index 56642816fdff..d564412a816b 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -503,6 +503,36 @@ static void drm_fb_rgb888_to_xrgb8888(struct iosys_map *dst, const unsigned int
>   		    drm_fb_rgb888_to_xrgb8888_line);
>   }
>   
> +static void drm_fb_xrgb8888_to_abgr8888_line(void *dbuf, const void *sbuf, unsigned int pixels)
> +{
> +	__le32 *dbuf32 = dbuf;
> +	const __le32 *sbuf32 = sbuf;
> +	unsigned int x;
> +	u32 pix;
> +
> +	for (x = 0; x < pixels; x++) {
> +		pix = le32_to_cpu(sbuf32[x]);
> +		pix = ((pix & 0xff000000) >> 24) << 24 |
> +		      ((pix & 0x00ff0000) >> 16) <<  0 |
> +		      ((pix & 0x0000ff00) >>  8) <<  8 |
> +		      ((pix & 0x000000ff) >>  0) << 16;
> +		*dbuf32++ = cpu_to_le32(pix);
> +	}
> +}

What does the Jetson device do with these alpha bits?

AFAIK the X channel's content is undefined. Shifting the bits into the A 
channel might result in wrong results in the general case. Better just 
set the alpha to 0xff unconditionally.

> +
> +static void drm_fb_xrgb8888_to_abgr8888(struct iosys_map *dst, const unsigned int *dst_pitch,
> +					const struct iosys_map *src,
> +					const struct drm_framebuffer *fb,
> +					const struct drm_rect *clip)
> +{
> +	static const u8 dst_pixsize[DRM_FORMAT_MAX_PLANES] = {
> +		4,
> +	};
> +
> +	drm_fb_xfrm(dst, dst_pitch, dst_pixsize, src, fb, clip, false,
> +		    drm_fb_xrgb8888_to_abgr8888_line);
> +}
> +
>   static void drm_fb_xrgb8888_to_xrgb2101010_line(void *dbuf, const void *sbuf, unsigned int pixels)
>   {
>   	__le32 *dbuf32 = dbuf;
> @@ -672,6 +702,11 @@ int drm_fb_blit(struct iosys_map *dst, const unsigned int *dst_pitch, uint32_t d
>   			drm_fb_rgb565_to_xrgb8888(dst, dst_pitch, src, fb, clip);
>   			return 0;
>   		}
> +	} else if (dst_format == DRM_FORMAT_ABGR8888) {
> +		if (fb_format == DRM_FORMAT_XRGB8888) {
> +			drm_fb_xrgb8888_to_abgr8888(dst, dst_pitch, src, fb, clip);
> +			return 0;
> +		}

For the other alpha-containing formats, we treat them like non-alpha 
formats (see the top of this function). Maybe just do the same here and 
then implement the conversion as drm_fb_xrgb8888_to_xbgr8888() helpers?

Best regards
Thomas

>   	} else if (dst_format == DRM_FORMAT_XRGB2101010) {
>   		if (fb_format == DRM_FORMAT_XRGB8888) {
>   			drm_fb_xrgb8888_to_xrgb2101010(dst, dst_pitch, src, fb, clip);

-- 
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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