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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
        Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
        Kieran Bingham <kbingham@kernel.org>,
        Simon Horman <horms@verge.net.au>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: vsps and channel indices (was: Re: [PATCH v3 1/2] arm64: dts: renesas: r8a77980: add FCPVD/VSPD/DU/LVDS support)
Date: Wed, 29 Aug 2018 12:12:19 +0300
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Hi Geert,

On Tuesday, 28 August 2018 15:10:52 EEST Geert Uytterhoeven wrote:
> Hi Sergei, Laurent, Kieran,
> 
> On Wed, Jun 13, 2018 at 10:11 PM Sergei Shtylyov wrote:
> > Describe the interconnected FCPVD0, VSPD0, DU, and LVDS0 devices in the
> > R8A77980 device tree...
> > 
> > Based on the original (and large) patch by Vladimir Barinov.
> > 
> > Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
> > Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > 
> > --- renesas.orig/arch/arm64/boot/dts/renesas/r8a77980.dtsi
> > +++ renesas/arch/arm64/boot/dts/renesas/r8a77980.dtsi
> > 
> > +               du: display@feb00000 {
> > +                       compatible = "renesas,du-r8a77980",
> > +                                    "renesas,du-r8a77970";
> > +                       reg = <0 0xfeb00000 0 0x80000>;
> > +                       interrupts = <GIC_SPI 256 IRQ_TYPE_LEVEL_HIGH>;
> > +                       clocks = <&cpg CPG_MOD 724>;
> > +                       clock-names = "du.0";
> > +                       power-domains = <&sysc R8A77980_PD_ALWAYS_ON>;
> > +                       resets = <&cpg 724>;
> > +                       vsps = <&vspd0>;
> 
> According to the bindings, the vsps property should also contain a
> channel index.
> 
> Laurent added the indices to r8a7795.dtsi, but r8a7795-es.dtsi overrides
> that with a version without the indices.
> Kieran included the indices when adding DU support for r8a77965 and
> r8a77995.
> 
> r8a7796.dtsi, r8a77970.dtsi, and r8a77980.dtsi lack the indices.
> 
> Commit fd57d77f9c649cf9 ("dt-bindings: display: rcar-du: Add a VSP channel
> index to the vsps DT property") says a backwards-compatibility mode can be
> implemented, but I fail to see how this can work, as rcar_du_vsps_init()
> will just return an error, which is propagated.
> 
> What am I missing?

We're missing a DT validator :-/

The vsps property shoould indeed contain indices. However, rcar_du_vsps_init() 
implements a backward-compatibility mode by checking the length of the 
property:

	cells = of_property_count_u32_elems(np, "vsps") / rcdu->num_crtcs - 1;

and using that as an argument to of_parse_phandle_with_fixed_args().

-- 
Regards,

Laurent Pinchart