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Subject: Re: [PATCH 5/8] arm64: dts: renesas: r8a77995: Add LVDS support
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, linux-arm-kernel@lists.infradead.org,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Simon Horman <horms@verge.net.au>,
        Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        Magnus Damm <magnus.damm@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        open list <linux-kernel@vger.kernel.org>
References: <1518683903-10681-1-git-send-email-kbingham@kernel.org>
 <1518683903-10681-6-git-send-email-kbingham@kernel.org>
 <CAMuHMdVKczZpoXgSDOSEJZb59LAZtbWsopRaa8PtHDoZcFEMTQ@mail.gmail.com>
From:   Kieran Bingham <kieran.bingham@ideasonboard.com>
Organization: Ideas on Board
Message-ID: <b8cc84ad-0a64-38f0-d8ac-ad9ae88c5912@ideasonboard.com>
Date:   Thu, 15 Feb 2018 12:41:05 +0000
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Hi Geert,

On 15/02/18 09:07, Geert Uytterhoeven wrote:
> Hi Kieran,
> 
> On Thu, Feb 15, 2018 at 9:38 AM, Kieran Bingham <kbingham@kernel.org> wrote:
>> From: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>>
>> The r8a77995 D3 platform has 2 LVDS channels connected to the DU.
>>
>> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> 
> I love your patch!
> Yet something to improve...
> 
>> --- a/arch/arm64/boot/dts/renesas/r8a77995.dtsi
>> +++ b/arch/arm64/boot/dts/renesas/r8a77995.dtsi
>> @@ -773,18 +773,70 @@
>>                                 port@1 {
>>                                         reg = <1>;
>>                                         du_out_lvds0: endpoint {
>> +                                               remote-endpoint = <&du_out_lvds0>;
>>                                         };
>>                                 };
>>
>>                                 port@2 {
>>                                         reg = <2>;
>>                                         du_out_lvds1: endpoint {
>> +                                               remote-endpoint = <&du_out_lvds1>;
>>                                         };
>>                                 };
>>                         };
>>                 };
>>         };
>>
>> +       lvds0: lvds@feb90000 {
>> +               compatible = "renesas,lvds-r8a77995";
>> +               reg = <0 0xfeb90000 0 0x20>;
>> +               clocks = <&cpg CPG_MOD 727>;
>> +               status = "disabled";
> 
> Missing resets, power-domains

Both lvds0, and lvds1 are actually the same 'module' (just different mappings
within the same IP block).

That means they will share clock, reset etc.

Will specifying the resets cause one to affect the other unduly?

like if one becomes un-used, will it power down? or is it refcounted, and will
gracefully handle both device nodes from the same device?

I'm already fairly sure clocks is fine for this - but it's just the reset's that
worry me. If the reset module tries to reset lvds0 for some reason - would lvds1
get reset as a side effect ...

Or perhaps that won't ever happen with an :

		power-domains = <&sysc R8A77995_PD_ALWAYS_ON>;
		resets = <&cpg 727>;

Regards
--
Kieran


> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>