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

[Liu Ying <victor.liu@nxp.com>]

On Mon, 2023-01-30 at 15:39 -0600, Rob Herring wrote:
> 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@nxp.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
> > > > +---
> > > > +$id: 
> > > > 
https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fschemas%2Fdisplay%2Fbridge%2Fnxp%2Cimx93-pdfc.yaml%23&data=05%7C01%7Cvictor.liu%40nxp.com%7C3e8db7ce3170451bc0e208db030a6ad0%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638107115502467822%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=c%2BQ%2Bhpov6L9b905ozKPrkWiTzaRD3ZFsEh0urw5evsQ%3D&reserved=0
> > > > +$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%7C3e8db7ce3170451bc0e208db030a6ad0%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638107115502467822%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=SkPZLJIR9uoqk4mRqSsfu963S%2Baa7xXmyCqzR36LJ30%3D&reserved=0
> > > > +
> > > > +title: NXP i.MX93 Parallel Display Format Configuration
> > > > +
> > > > +maintainers:
> > > > +  - Liu Ying <victor.liu@nxp.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.

Do you mean that we can keep this schema and need to allow child
devices in fsl,imx93-media-blk-ctrl.yaml?

Cc'ing Peng.

Peng, it appears that you are listed in the maintainers of fsl,imx93-
media-blk-ctrl.yaml. I think it needs to be extended to allow child
devices. Do you consider to do that?

Regards,
Liu Ying

> 
> Rob