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Date:   Tue, 20 Sep 2022 20:32:34 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Marco Felsch <m.felsch@pengutronix.de>
Cc:     Sakari Ailus <sakari.ailus@linux.intel.com>, mchehab@kernel.org,
        robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
        kishon@ti.com, vkoul@kernel.org, hverkuil@xs4all.nl,
        jacopo@jmondi.org, kieran.bingham+renesas@ideasonboard.com,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org,
        kernel@pengutronix.de
Subject: Re: [PATCH v2 3/4] media: dt-bindings: add bindings for Toshiba
 TC358746
Message-ID: <Yyn5MqqKYH7VpFhw@pendragon.ideasonboard.com>
References: <20220916134535.128131-1-m.felsch@pengutronix.de>
 <20220916134535.128131-4-m.felsch@pengutronix.de>
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 <20220919100844.bb7tzbql2vpk76xz@pengutronix.de>
 <YyhDO4ohv47uIij2@paasikivi.fi.intel.com>
 <YyhKoDxFoobY9vBd@pendragon.ideasonboard.com>
 <20220920152632.mjpgpmelvx4ya4k7@pengutronix.de>
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Hi Marco,

On Tue, Sep 20, 2022 at 05:26:32PM +0200, Marco Felsch wrote:
> On 22-09-19, Laurent Pinchart wrote:
> > 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.
> 
> Okay, I will make it required.
> 
> > > Why do you have hsync-active and vsync-active if both are always zero? Can
> > > the hardware not support other configuration?
> 
> Sure the device supports toggling the logic but it is not implemented.
> So the bindings needs to enforce it to 0 right now. As soon as it is
> implemented & tested, we can say that both is supported :)

Bindings are not supposed to be limited by the existing driver
implementation, so you can already allow both polarities, and just
reject the unsupported options in the driver at probe time. Future
updates to the driver won't require a binding change.

-- 
Regards,

Laurent Pinchart