linux-kernel - Re: [PATCH 1/2] dt-bindings: display: bridge: Add NXP i.MX93 parallel display format configuration

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Message-ID: <20230130213904.GA3569183-robh@kernel.org>
Date:   Mon, 30 Jan 2023 15:39:04 -0600
From:   Rob Herring <robh@...nel.org>
To:     Liu Ying <victor.liu@....com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        andrzej.hajda@...el.com, neil.armstrong@...aro.org,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com,
        daniel@...ll.ch, krzysztof.kozlowski+dt@...aro.org,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com
Subject: Re: [PATCH 1/2] dt-bindings: display: bridge: Add NXP i.MX93
 parallel display format configuration

On Mon, Jan 30, 2023 at 04:39:05PM +0800, Liu Ying wrote:
> On Sun, 2023-01-29 at 12:46 +0100, Krzysztof Kozlowski wrote:
> > On 28/01/2023 04:47, Liu Ying wrote:
> > > NXP i.MX93 mediamix blk-ctrl contains one DISPLAY_MUX register
> > > which
> > > configures parallel display format by using the
> > > "PARALLEL_DISP_FORMAT"
> > > field. Add device tree bindings for the display format
> > > configuration.
> > > 
> > > Signed-off-by: Liu Ying <victor.liu@....com>
> > > ---
> > >  .../display/bridge/nxp,imx93-pdfc.yaml        | 78
> > > +++++++++++++++++++
> > >  1 file changed, 78 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/display/bridge/nxp,imx93-
> > > pdfc.yaml
> > > 
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/bridge/nxp,imx93-
> > > pdfc.yaml
> > > b/Documentation/devicetree/bindings/display/bridge/nxp,imx93-
> > > pdfc.yaml
> > > new file mode 100644
> > > index 000000000000..a84bfb46b01d
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/bridge/nxp,imx93-
> > > pdfc.yaml
> > > @@ -0,0 +1,78 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: 
> > > https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fschemas%2Fdisplay%2Fbridge%2Fnxp%2Cimx93-pdfc.yaml%23&data=05%7C01%7Cvictor.liu%40nxp.com%7C7fb1b69849974435787008db01ee832c%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638105896131701918%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kkX5B45NTsmDKKzxjOiE6MaE4zkMVbMe4ILammVSwMc%3D&reserved=0
> > > +$schema: 
> > > https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fmeta-schemas%2Fcore.yaml%23&data=05%7C01%7Cvictor.liu%40nxp.com%7C7fb1b69849974435787008db01ee832c%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638105896131701918%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=vIVpdEjIo6H3V8T7iTbDwz4Bmn0d%2BQB4BCJNJ0OzKJw%3D&reserved=0
> > > +
> > > +title: NXP i.MX93 Parallel Display Format Configuration
> > > +
> > > +maintainers:
> > > +  - Liu Ying <victor.liu@....com>
> > > +
> > > +description: |
> > > +  The i.MX93 mediamix blk-ctrl contains one DISPLAY_MUX register
> > > which
> > > +  configures parallel display format by using the
> > > "PARALLEL_DISP_FORMAT"
> > > +  field.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: nxp,imx93-pdfc
> > 
> > 
> > Based on description, I have doubts this is a separate bridge device.
> > Why this is not part of display driver/bindings?
> 
> The relevant display controller in i.MX93 SoC is LCDIF. From hardware
> design PoV, the parallel display format configuration logic is not a
> part of LCDIF. Instead, it's a part of i.MX93 mediamix blk-ctrl. The
> blk-ctrl includes controls for miscellaneous devices with small logics,
> like this parallel display format configuration, LVDS Display
> Bridge(LDB, see fsl,ldb.yaml) and so on. The below pipeline describes
> data flow of a parallel display LCD panel:
> 
> DRAM -> LCDIF -> parallel display format configuration -> LCD panel
> 
> So, the parallel display format configuration appears to be a separate
> bridge.
> 
> > 
> > We do not create usually devices for single registers, because they
> > are
> > not a devices. Devices are a bit more complex - have some pin
> > inputs/outputs, not a register only. Of course there are exception,
> > but
> > this one does not look like one.
> 
> IMHO, this one is a standalone device although it is controlled by one
> single register. It's input pins connect to LCDIF and output pins
> connect to i.MX93 SoC's pins/pads.

Fair enough. It needs to be defined as part of the mediamix blkctrl 
schema though.

Rob