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

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Date:   Tue, 28 Sep 2021 11:08:58 +0200
From:   Marek Vasut <marex@...x.de>
To:     Guido Günther <agx@...xcpu.org>
Cc:     Stefan Agner <stefan@...er.ch>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.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>,
        Sam Ravnborg <sam@...nborg.org>,
        Lucas Stach <l.stach@...gutronix.de>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH] drm: mxsfb: Set proper default bus format when using a
 bridge

On 9/28/21 10:55 AM, Guido Günther wrote:
> 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")
> 
> Signed-off-by: Guido Günther <agx@...xcpu.org>
> ---
> 
> I'll look at what needs to be done in nwl separately but this also
> unbreaks other bridge seupts that don't to format negotiation yet.
> 
>   drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index af6c620adf6e..4ef94cf686b0 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -369,6 +369,8 @@ 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)
> +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;

Shouldn't the NWL bridge return the correct format ?