linux-kernel - RE: [PATCH 10/22] dt-bindings: display: renesas,rzg2l-du: Add support for RZ/G3E SoC

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Message-ID:
 <TY3PR01MB11346DF85F8F7EA9ADDED16EB868CA@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Thu, 15 Jan 2026 07:48:31 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: geert <geert@...ux-m68k.org>, Tommaso Merciai
	<tommaso.merciai.xr@...renesas.com>
CC: Krzysztof Kozlowski <krzk@...nel.org>, Tommaso Merciai
	<tomm.merciai@...il.com>, "linux-renesas-soc@...r.kernel.org"
	<linux-renesas-soc@...r.kernel.org>, Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
	laurent.pinchart <laurent.pinchart@...asonboard.com>, Jonas Karlman
	<jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, David Airlie
	<airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>, Michael Turquette
	<mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, magnus.damm
	<magnus.damm@...il.com>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-clk@...r.kernel.org"
	<linux-clk@...r.kernel.org>
Subject: RE: [PATCH 10/22] dt-bindings: display: renesas,rzg2l-du: Add support
 for RZ/G3E SoC

Hi Geert,

Thanks for the feedback.

> -----Original Message-----
> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: 14 January 2026 12:38
> Subject: Re: [PATCH 10/22] dt-bindings: display: renesas,rzg2l-du: Add support for RZ/G3E SoC
> 
> Hi Tommaso,
> 
> On Wed, 3 Dec 2025 at 14:42, Tommaso Merciai <tommaso.merciai.xr@...renesas.com> wrote:
> > On Wed, Dec 03, 2025 at 09:23:53AM +0100, Krzysztof Kozlowski wrote:
> > > On Wed, Nov 26, 2025 at 03:07:22PM +0100, Tommaso Merciai wrote:
> > > > The RZ/G3E Soc has 2 LCD controller (LCDC), contain a Frame
> > > > Compression Processor (FCPVD), a Video Signal Processor (VSPD),
> > > > Video Signal Processor (VSPD), and Display Unit (DU).
> > > >
> > > >  - LCDC0 supports DSI and LVDS (single or dual-channel) outputs.
> > > >  - LCDC1 supports DSI, LVDS (single-channel), and RGB outputs.
> > > >
> > > > Add then two new SoC-specific compatible strings 'renesas,r9a09g047-du0'
> > > > and 'renesas,r9a09g047-du1'.
> > >
> > > LCDC0/1 but compatibles du0/du1...
> > >
> > > What are the differences between DU0 and DU1? Just different
> > > outputs? Is the programming model the same?
> >
> > The hardware configurations are different: these are two distinct hardware blocks.
> >
> > Based on the block diagrams shown in Figures 9.4-2 (LCDC1) and 9.4-1
> > (LCDC0), the only difference concerns the output, but this variation
> > is internal to the hardware blocks themselves.
> > Therefore, LCDC0 and LCDC1 are not identical blocks, and their
> > programming models differ as a result.
> >
> > In summary, although most of the internal functions are the same, the
> > two blocks have output signals connected to different components within the SoC.
> > This requires different hardware configurations and inevitably leads
> > to different programming models for LCDC0 and LCDC1.
> 
> Isn't that merely an SoC integration issue?
> Are there any differences in programming LCDC0 or LCDC1 for the common output types supported by both
> (single channel LVDS and 4-lane MIPI-DSI)?

Dual LVDS case, dot clock from LCDC0 is used in both LCDC's.
Standalone LVDS and DSI the programming flow is same.

> 
> Of there are no such differences, both instances should use the same compatible value.

Then we need to use a property called display-id, to describe the supported
output types in bindings, right??

Display-id=0 {LVDS, DSI)
Display-id=1 {LVDS, DSI, DPI)

Cheers,
Biju