Re: [PATCH v2 3/4] media: dt-bindings: add bindings for Toshiba TC358746

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Sep 19, 2022 at 10:23:55AM +0000, Sakari Ailus wrote:
> On Mon, Sep 19, 2022 at 12:08:44PM +0200, Marco Felsch wrote:
> > On 22-09-18, Laurent Pinchart wrote:
> > > On Fri, Sep 16, 2022 at 03:45:34PM +0200, Marco Felsch wrote:
> > > > Add the bindings for the Toshiba TC358746 Parallel <-> MIPI-CSI bridge
> > > > driver.
> > > > 
> > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > > ---
> > > > Changelog:
> > > > 
> > > > v2:
> > > > - addded Robs r-b
> > > > - s/than/then/
> > > > - added hsync/vsync/bus-type, make hsync/vsync required
> > > > - fix example indent
> > > > 
> > > >  .../bindings/media/i2c/toshiba,tc358746.yaml  | 179 ++++++++++++++++++
> > > >  1 file changed, 179 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > > > new file mode 100644
> > > > index 000000000000..1fa574400bc2
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > > > @@ -0,0 +1,179 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/media/i2c/toshiba,tc358746.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Toshiba TC358746 Parallel to MIPI CSI2 Bridge
> > > > +
> > > > +maintainers:
> > > > +  - Marco Felsch <kernel@pengutronix.de>
> > > > +
> > > > +description: |-
> > > > +  The Toshiba TC358746 converts a parallel video stream into a MIPI CSI-2
> > > > +  stream. The direction can be either parallel-in -> csi-out or csi-in ->
> > > > +  parallel-out The chip is programmable trough I2C and SPI but the SPI
> > > > +  interface is only supported in parallel-in -> csi-out mode.
> > > > +
> > > > +  Note that the current device tree bindings only support the
> > > > +  parallel-in -> csi-out path.
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    const: toshiba,tc358746
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  clocks:
> > > > +    description:
> > > > +      The phandle to the reference clock source. This corresponds to the
> > > > +      hardware pin REFCLK.
> > > > +    maxItems: 1
> > > > +
> > > > +  clock-names:
> > > > +    const: refclk
> > > > +
> > > > +# The bridge can act as clock provider for the sensor. To enable this support
> > > > +# #clock-cells must be specified. Attention if this feature is used then the
> > > > +# mclk rate must be at least: (2 * link-frequency) / 8
> > > > +#                             `------------------´   ^
> > > > +#                             internal PLL rate   smallest possible mclk-div
> > > > +  "#clock-cells":
> > > > +    const: 0
> > > > +
> > > > +  clock-output-names:
> > > > +    description:
> > > > +      The clock name of the MCLK output, the default name is tc358746-mclk.
> > > > +    maxItems: 1
> > > > +
> > > > +  vddc-supply:
> > > > +    description: Digital core voltage supply, 1.2 volts
> > > > +
> > > > +  vddio-supply:
> > > > +    description: Digital I/O voltage supply, 1.8 volts
> > > > +
> > > > +  vddmipi-supply:
> > > > +    description: MIPI CSI phy voltage supply, 1.2 volts
> > > > +
> > > > +  reset-gpios:
> > > > +    description:
> > > > +      The phandle and specifier for the GPIO that controls the chip reset.
> > > > +      This corresponds to the hardware pin RESX which is physically active low.
> > > > +    maxItems: 1
> > > > +
> > > > +  ports:
> > > > +    $ref: /schemas/graph.yaml#/properties/ports
> > > > +    properties:
> > > > +      port@0:
> > > > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > > > +        description: Input port
> > > > +
> > > > +        properties:
> > > > +          endpoint:
> > > > +            $ref: /schemas/media/video-interfaces.yaml#
> > > > +            unevaluatedProperties: false
> > > > +
> > > > +            properties:
> > > > +              hsync-active:
> > > > +                enum:
> > > > +                  - 0 # Hvalid active high
> > > > +              vsync-active:
> > > > +                enum:
> > > > +                  - 0 # Vvalid active high
> > > > +              bus-type:
> > > > +                enum:
> > > > +                  - 5 # Parallel
> > > > +
> > > > +            required:
> > > > +              - hsync-active
> > > > +              - vsync-active
> > > 
> > > Let's make bus-type required too, to prepare for BT.656 support.
> > 
> > I would have done it when the BT.656 support is added. Since the BT.656
> > don't require the sync signals I would have made a descision:
> >  - either: hsync/vsync present -> parallel with external syncs, or
> >  - bus-type present -> parallel bus with embedded syncs.
> > 
> > So we don't bother the system-integrator with specifying unnecessary
> > properties. Also having v/hsync required in place with the bus-type (set
> > to bt.656) can cause confusion about the final used mode.
> 
> The V4L2 fwnode framework can guess the type of the bus but it's not
> recommended to use the feature.

Explicit bus types in DT indeed makes it easier for drivers, so if a
device can support multiple bus types (even if not implemented yet in
the corresponding drivers), the property should be there.

> Why do you have hsync-active and vsync-active if both are always zero? Can
> the hardware not support other configuration?

-- 
Regards,

Laurent Pinchart