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Date: Tue, 28 Sep 2021 11:27:49 +0200 From: Lucas Stach <l.stach@...gutronix.de> To: Guido Günther <agx@...xcpu.org>, Marek Vasut <marex@...x.de> 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>, 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 Am Dienstag, dem 28.09.2021 um 11:19 +0200 schrieb Guido Günther: > Hi, > On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote: > > 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 ? > > Yes it should and I'll send a separate patch for that but we currently > don't do anything meaningful at all if the bridge doesn't do format > negotiation and then fail setup in mxsfb_set_formats(). > > I think we should at least preserve the status quo (as we do with the > non bridge case in b776b0f00f24 too). > > We could have a warning to spot drivers that don't do that yet and hence > the generic code returns MEDIA_BUS_FMT_FIXED. > That sounds sensible. Using a default format if we don't know what to do is going to be a unpleasant surprise for those with a display pipeline that doesn't work with the default format. So please add a dev_warn when we are doing this fallback. Also I would argue that the NWL fix is the patch that should go in the stable tree. This one should only be a additional safety net, so I would drop the Fixes tag. Regards, Lucas
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