linux-kernel - Re: [PATCH/RFC 07/12] drm: rcar-du: lvds: Add support for dual link panels

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Date:   Mon, 5 Aug 2019 12:48:32 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Fabrizio Castro <fabrizio.castro@...renesas.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Simon Horman <horms@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>
Subject: Re: [PATCH/RFC 07/12] drm: rcar-du: lvds: Add support for dual link
 panels

Hi Fabrizio,

On Mon, Aug 05, 2019 at 09:12:34AM +0000, Fabrizio Castro wrote:
> > From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Sent: 02 August 2019 09:20
> > Subject: Re: [PATCH/RFC 07/12] drm: rcar-du: lvds: Add support for dual link panels
> > 
> > Hi Fabrizio,
> > 
> > Thank you for the patch.
> > 
> > On Fri, Aug 02, 2019 at 08:34:04AM +0100, Fabrizio Castro wrote:
> > > If the display comes with two ports, assume it supports dual
> > > link.
> > >
> > > Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> > > ---
> > >  drivers/gpu/drm/rcar-du/rcar_lvds.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> > > index 2d54ae5..97c51c2 100644
> > > --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
> > > +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> > > @@ -751,6 +751,9 @@ static int rcar_lvds_parse_dt(struct rcar_lvds *lvds)
> > >  			ret = -EPROBE_DEFER;
> > >  			goto done;
> > >  		}
> > > +		if (lvds->info->quirks & RCAR_LVDS_QUIRK_DUAL_LINK)
> > > +			lvds->dual_link = of_graph_get_endpoint_count(remote)
> > > +					== 2;
> > 
> > This is a bit of a hack, as I think the information should be queried
> > from the panel, like we do for bridges. I'd say we can live with this
> > for now, but as the data swap flag should come from the panel as well,
> > we will need infrastructure for that, and we can as well through the
> > dual link flag there at the same time.
> 
> I totally agree, this is a nasty hack, my series is missing the infrastructure
> for describing this information
> 
> > I think we should use the drm_bridge_timings structure for this purpose,
> > as it would make life more difficult for users of drm_bridge and
> > drm_panel to have two different structures (especially when wrapping a
> > drm_panel with drm_panel_bridge_add()). The structure could be renamed
> > if desired.
> 
> I am not too sure using drm_bridge_timings for panels would make everybody
> happy? Is there any alternative? Perhaps this calls for a new struct we could
> embed in both drm_bridge_timings and some drm_panel_<whatever> data
> structure?

I think we could simply rename the structure, all its fields apply to
panels too.

> > >  	}
> > >
> > >  	if (lvds->dual_link) {

-- 
Regards,

Laurent Pinchart