linux-kernel - Re: [PATCH v2 5/5] drm: mxsfb: Set proper default bus format when using a bridge

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Message-ID: <3b557e62ad8f313d8fdfb352730cb9a0c5c2eb57.camel@pengutronix.de>
Date:   Mon, 04 Oct 2021 09:58:37 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Guido Günther <agx@...xcpu.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Marek Vasut <marex@...x.de>,
        Stefan Agner <stefan@...er.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Ondrej Jirman <megous@...ous.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 5/5] drm: mxsfb: Set proper default bus format when
 using a bridge

Am Montag, dem 04.10.2021 um 09:27 +0200 schrieb Guido Günther:
> If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
> returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
> that case.
> 
> This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
> 
> Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
> 
I don't think this qualifies for stable, so I would drop this tag, as
the stable maintainers are quite trigger happy to pull in patches with
a fixes tag. Also the subject isn't quite correct, this isn't setting a
"proper" bus format, but rather adds a fallback. Other than that:

Reviewed-by: Lucas Stach <l.stach@...gutronix.de>

Regards,
Lucas

> Reported-by: Martin Kepplinger <martink@...teo.de>
> Signed-off-by: Guido Günther <agx@...xcpu.org>

> ---
>  drivers/gpu/drm/mxsfb/mxsfb_kms.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index d6abd2077114..e3fbb8b58d5d 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -369,6 +369,12 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
>  			drm_atomic_get_new_bridge_state(state,
>  							mxsfb->bridge);
>  		bus_format = bridge_state->input_bus_cfg.format;
> +		if (bus_format == MEDIA_BUS_FMT_FIXED) {
> +			dev_warn_once(drm->dev,
> +				      "Bridge does not provide bus format, assuming MEDIA_BUS_FMT_RGB888_1X24.\n"
> +				      "Please fix bridge driver by handling atomic_get_input_bus_fmts.\n");
> +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +		}
>  	}
>  
>  	/* If there is no bridge, use bus format from connector */