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

[Liu Ying]

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@xxxxxxx>
> > ---
> >  .../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@xxxxxxx>
> > +
> > +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.

> 
> > +
> > +  reg:
> > +    maxItems: 1
> 
> Your driver tells different story:
> 
> syscon_node_to_regmap(dev->of_node->parent);
> 
> (which also points to fact this is not a separate device)

This function call gets the parent device's(mediamix blk-ctrl's)
regmap, like fsl-ldb.c does. Same to LDB, the parallel display format
configuration device is a child device of the mediamix blk-ctrl device.

Regards,
Liu Ying

> 
> Best regards,
> Krzysztof
>