linux-kernel - Re: [PATCH] media: bcm2835-unicam: Remove RGB24 support

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Message-ID: <20250609003751.GD14545@pendragon.ideasonboard.com>
Date: Mon, 9 Jun 2025 03:37:51 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>,
	Dave Stevenson <dave.stevenson@...pberrypi.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Hans Verkuil <hverkuil@...all.nl>,
	Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>,
	Naushir Patuck <naush@...pberrypi.com>, linux-media@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: bcm2835-unicam: Remove RGB24 support

Hi Maxime,

Thank you for the patch.

On Fri, Jun 06, 2025 at 04:53:03PM +0200, Maxime Ripard wrote:
> The RGB24 V4L2 format is defined as a pixel format with 8 bits per
> components, with the components being in the red, green, and blue order
> from left to right.
> 
> The RGB MIPI-CSI2 is defined in the specification (Section 11.3.1,
> RGB888) with blue coming first, then green, then red. So the opposite of
> what V4L2 means by RGB.
> 
> Since the hardware cannot reorder the components, this means that when
> selecting the RGB24 format, you get inverted red and blue components
> compared to what you'd expect.
> 
> The driver already supports BGR24, so we can simply remove the RGB24
> format from the driver.

The only reason I could think of to explain why the driver exposes
V4L2_PIX_FMT_RGB24 is to support CSI-2 sources that transfer RGB888 data
with a non-standard order. I don't know what hardware would do that.
Dave, Naush, do you recall why this pixel format is supported by the
unicam driver ?

> Fixes: 392cd78d495f ("media: bcm2835-unicam: Add support for CCP2/CSI2 camera interface")
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---
>  drivers/media/platform/broadcom/bcm2835-unicam.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
> index f10064107d543caf867249d0566a0f42d6d8c4c6..1f549019efd53c9aae83193e74f1a3601ebf274d 100644
> --- a/drivers/media/platform/broadcom/bcm2835-unicam.c
> +++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
> @@ -338,15 +338,10 @@ static const struct unicam_format_info unicam_image_formats[] = {
>  	/* RGB Formats */
>  		.fourcc		= V4L2_PIX_FMT_RGB565, /* gggbbbbb rrrrrggg */
>  		.code		= MEDIA_BUS_FMT_RGB565_1X16,
>  		.depth		= 16,
>  		.csi_dt		= MIPI_CSI2_DT_RGB565,
> -	}, {
> -		.fourcc		= V4L2_PIX_FMT_RGB24, /* rgb */
> -		.code		= MEDIA_BUS_FMT_RGB888_1X24,
> -		.depth		= 24,
> -		.csi_dt		= MIPI_CSI2_DT_RGB888,
>  	}, {
>  		.fourcc		= V4L2_PIX_FMT_BGR24, /* bgr */
>  		.code		= MEDIA_BUS_FMT_BGR888_1X24,
>  		.depth		= 24,
>  		.csi_dt		= MIPI_CSI2_DT_RGB888,
> 
> ---
> base-commit: 0ff41df1cb268fc69e703a08a57ee14ae967d0ca
> change-id: 20250606-rpi-unicam-rgb-bgr-fix-d1b6f46a75ad

-- 
Regards,

Laurent Pinchart