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Date:   Thu, 31 Oct 2019 16:11:41 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc:     mchehab@kernel.org, robh+dt@kernel.org, sakari.ailus@iki.fi,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        c.barrett@framos.com, a.brela@framos.com, peter.griffin@linaro.org
Subject: Re: [PATCH v4 1/2] dt-bindings: media: i2c: Add IMX296 CMOS sensor
 binding
Message-ID: <20191031141141.GD5018@pendragon.ideasonboard.com>
References: <20191030094902.32582-1-manivannan.sadhasivam@linaro.org>
 <20191030094902.32582-2-manivannan.sadhasivam@linaro.org>
 <20191031131538.GA9170@pendragon.ideasonboard.com>
 <20191031134512.GB24273@mani>
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In-Reply-To: <20191031134512.GB24273@mani>
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Hi Mani,

On Thu, Oct 31, 2019 at 07:15:12PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Oct 31, 2019 at 03:15:38PM +0200, Laurent Pinchart wrote:
> > On Wed, Oct 30, 2019 at 03:19:01PM +0530, Manivannan Sadhasivam wrote:
> >> Add YAML devicetree binding for IMX296 CMOS image sensor. Let's also
> >> add MAINTAINERS entry for the binding and driver.
> >> 
> >> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> >> ---
> >>  .../devicetree/bindings/media/i2c/imx296.yaml | 94 +++++++++++++++++++
> >>  MAINTAINERS                                   |  8 ++
> >>  2 files changed, 102 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/media/i2c/imx296.yaml
> >> 
> >> diff --git a/Documentation/devicetree/bindings/media/i2c/imx296.yaml b/Documentation/devicetree/bindings/media/i2c/imx296.yaml
> >> new file mode 100644
> >> index 000000000000..c04ec2203268
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/media/i2c/imx296.yaml
> >> @@ -0,0 +1,94 @@
> >> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> >> +%YAML 1.2
> >> +---
> >> +$id: http://devicetree.org/schemas/media/i2c/imx296.yaml#
> >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >> +
> >> +title: Sony IMX296 1/2.8-Inch CMOS Image Sensor
> >> +
> >> +maintainers:
> >> +  - Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> >> +
> >> +description: |-
> >> +  The Sony IMX296 is a 1/2.9-Inch active pixel type CMOS Solid-state image
> >> +  sensor with square pixel array and 1.58 M effective pixels. This chip
> >> +  features a global shutter with variable charge-integration time. It is
> >> +  programmable through I2C and 4-wire interfaces. The sensor output is
> >> +  available via CSI-2 serial data output (1 Lane).
> >> +
> >> +properties:
> >> +  compatible:
> >> +    const: sony,imx296
> >> +
> >> +  reg:
> >> +    maxItems: 1
> >> +
> >> +  clocks:
> >> +    maxItems: 1
> >> +
> >> +  clock-names:
> >> +    description:
> >> +      Input clock for the sensor.
> >> +    items:
> >> +      - const: mclk
> > 
> > The pin is named INCK, let's name the clock accordingly.
> 
> Okay, I thought generic names are preferred here!
>  
> >> +  clock-frequency:
> >> +    description:
> >> +      Frequency of the mclk clock in Hertz.
> > 
> > This shouldn't be needed, you can retrieve the clock frequency at
> > runtime from the clock source.
> 
> Unless the clock source is a fixed one! What if the clock source comes from
> SoC? We need to set the rate, right?

In that case, if you want to hardcode the clock in DT, the preferred way
is to use the assigned-clock-rates property. Otherwise, if the driver
requires a specific clock frequency, it's better to hardcode it in the
driver itself. In this specific case, I think assigned-clock-rates is
best as the device can support three different clock frequencies.

> >> +  vddo-supply:
> >> +    description:
> >> +      Definition of the regulator used as interface power supply.
> >> +
> >> +  vdda-supply:
> >> +    description:
> >> +      Definition of the regulator used as analog power supply.
> >> +
> >> +  vddd-supply:
> >> +    description:
> >> +      Definition of the regulator used as digital power supply.
> > 
> > Do we really need three regulators ? I agree that the sensor has three
> > power rails, but aren't they usually powered by regulators that are
> > tied together, without individual control ? The IMX926 specifications
> > require the three power supplies to raise within 200ms, which we should
> > be able to ensure in software. What does your board use, does it have
> > multiple GPIOs to control each power supply ? If not I wonder if we
> > could just define vddd-supply now, and add vdda-supply and vddo-supply
> > later if we need to support systems that can control the supplies
> > individually.
> 
> The whole power supply model is a bit rotten. In my case, there are 3 different
> regulators used with no software control. So, I can't control the rise time
> (I assume that they are handled by the external power regulator itself).
> 
> So to be sane, I just documented with the assumption of fixed-regulators.

Should we then go for one supply, and add the other two when (and if)
needed ?

> >> +  reset-gpios:
> >> +    description:
> >> +      The phandle and specifier for the GPIO that controls sensor reset.
> >> +    maxItems: 1
> >> +
> >> +  port: true
> >> +
> >> +required:
> >> +  - compatible
> >> +  - reg
> >> +  - clocks
> >> +  - clock-names
> >> +  - clock-frequency
> >> +  - vddo-supply
> >> +  - vdda-supply
> >> +  - vddd-supply
> >> +
> >> +additionalProperties: false
> >> +
> >> +examples:
> >> +  - |
> >> +    #include <dt-bindings/gpio/gpio.h>
> >> +
> >> +    imx296: camera-sensor@1a {
> >> +        compatible = "sony,imx296";
> >> +        reg = <0x1a>;
> >> +        reset-gpios = <&msmgpio 35 GPIO_ACTIVE_LOW>;
> >> +        pinctrl-names = "default";
> >> +        pinctrl-0 = <&camera_rear_default>;
> >> +        clocks = <&gcc 90>;
> >> +        clock-names = "mclk";
> >> +        clock-frequency = <37125000>;
> >> +        vddo-supply = <&camera_vddo_1v8>;
> >> +        vdda-supply = <&camera_vdda_3v3>;
> >> +        vddd-supply = <&camera_vddd_1v2>;
> >> +
> >> +        port {
> >> +            imx296_ep: endpoint {
> >> +                remote-endpoint = <&csiphy0_ep>;
> >> +            };
> >> +        };
> >> +    };
> >> +
> >> +...
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index 55199ef7fa74..51194bb2c392 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -15140,6 +15140,14 @@ S:	Maintained
> >>  F:	drivers/media/i2c/imx274.c
> >>  F:	Documentation/devicetree/bindings/media/i2c/imx274.txt
> >>  
> >> +SONY IMX296 SENSOR DRIVER
> >> +M:	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> >> +L:	linux-media@vger.kernel.org
> >> +T:	git git://linuxtv.org/media_tree.git
> >> +S:	Maintained
> >> +F:	drivers/media/i2c/imx296.c
> >> +F:	Documentation/devicetree/bindings/media/i2c/imx296.yaml
> >> +
> >>  SONY IMX319 SENSOR DRIVER
> >>  M:	Bingbu Cao <bingbu.cao@intel.com>
> >>  L:	linux-media@vger.kernel.org

-- 
Regards,

Laurent Pinchart