linux-kernel - Re: [PATCH 6/7] drm/vc4: dpi: Change the default DPI format to being 18bpp, not 24.

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Date:   Sat, 15 Oct 2022 20:13:38 +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 6/7] drm/vc4: dpi: Change the default DPI format to being
 18bpp, not 24.

Hi Maxime (and Dave),

Thank you for the patch.

On Thu, Oct 13, 2022 at 11:56:50AM +0200, Maxime Ripard wrote:
> From: Dave Stevenson <dave.stevenson@...pberrypi.com>
> 
> DPI hasn't really been used up until now, so the default has
> been meaningless.
> In theory we should be able to pass the desired format for the
> adjacent bridge chip through, but framework seems to be missing
> for that.

Doesn't the bridge infrastructure allow that ? Or maybe this commit
message was written a while ago, before it was possible ?

In any case, it would be nice to use the bus format exposed by the next
bridge in the chain, but that can be done in a subsequent step. The new
default seems reasonable.

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

> As the main device to use DPI is the VGA666 or Adafruit Kippah,
> both of which use RGB666, change the default to being RGB666 instead
> of RGB888.
> 
> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_dpi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> index ecbe4cd87036..fdae02760b6d 100644
> --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> @@ -150,8 +150,8 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
>  	}
>  	drm_connector_list_iter_end(&conn_iter);
>  
> -	/* Default to 24bit if no connector or format found. */
> -	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
> +	/* Default to 18bit if no connector or format found. */
> +	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_18BIT_666_RGB_1, DPI_FORMAT);
>  
>  	if (connector) {
>  		if (connector->display_info.num_bus_formats) {
> 

-- 
Regards,

Laurent Pinchart