linux-kernel - Re: [PATCH 7/7] drm/vc4: dpi: Fix format mapping for RGB565

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Date:   Sat, 15 Oct 2022 20:19:03 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Maxime Ripard <mripard@...nel.org>, Eric Anholt <eric@...olt.net>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Rob Herring <robh@...nel.org>,
        Emma Anholt <emma@...olt.net>, dri-devel@...ts.freedesktop.org,
        Joerg Quinten <aBUGSworstnightmare@...il.com>,
        Chris Morgan <macromorgan@...mail.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] drm/vc4: dpi: Fix format mapping for RGB565

Hi Maxime and Dave,

Thank you for the patch.

On Thu, Oct 13, 2022 at 11:56:51AM +0200, Maxime Ripard wrote:
> From: Dave Stevenson <dave.stevenson@...pberrypi.com>
> 
> The mapping is incorrect for RGB565_1X16 as it should be
> DPI_FORMAT_18BIT_666_RGB_1 instead of DPI_FORMAT_18BIT_666_RGB_3.

The driver includes the following macro definitions and comments:

/* Outputs 00000000rrrrrggggggbbbbb */
# define DPI_FORMAT_16BIT_565_RGB_1     1
/* Outputs 000rrrrr00gggggg000bbbbb */
# define DPI_FORMAT_16BIT_565_RGB_2     2
/* Outputs 00rrrrr000gggggg00bbbbb0 */
# define DPI_FORMAT_16BIT_565_RGB_3     3

MEDIA_BUS_FMT_RGB565_1X16 is defined as described in
https://linuxtv.org/downloads/v4l-dvb-apis/userspace-api/v4l/subdev-formats.html#id3:

Bit  | 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
Data | r4 r3 r2 r1 r0 g5 g4 g3 g2 g1 g0 b4 b3 b2 b1 b0 

This seems to match DPI_FORMAT_16BIT_565_RGB_1 indeed.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> Fixes: 08302c35b59d ("drm/vc4: Add DPI driver")
> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_dpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> index fdae02760b6d..a7bebfa5d5b0 100644
> --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> @@ -185,7 +185,7 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
>  						       DPI_FORMAT);
>  				break;
>  			case MEDIA_BUS_FMT_RGB565_1X16:
> -				dpi_c |= VC4_SET_FIELD(DPI_FORMAT_16BIT_565_RGB_3,
> +				dpi_c |= VC4_SET_FIELD(DPI_FORMAT_16BIT_565_RGB_1,
>  						       DPI_FORMAT);
>  				break;
>  			case MEDIA_BUS_FMT_RGB565_1X24_CPADHI:
> 

-- 
Regards,

Laurent Pinchart