linux-kernel - Re: [PATCH v4 1/2] dt-bindings: media: i2c: Add IMX296 CMOS sensor binding

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Message-ID: <20191031165444.GE5018@pendragon.ideasonboard.com>
Date:   Thu, 31 Oct 2019 18:54:44 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mchehab@...nel.org, robh+dt@...nel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        c.barrett@...mos.com, a.brela@...mos.com, peter.griffin@...aro.org
Subject: Re: [PATCH v4 1/2] dt-bindings: media: i2c: Add IMX296 CMOS sensor
 binding

Hi Sakari,

On Thu, Oct 31, 2019 at 04:28:17PM +0200, Sakari Ailus wrote:
> On Thu, Oct 31, 2019 at 04:11:41PM +0200, Laurent Pinchart wrote:
> > 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@...aro.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@...aro.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.
> 
> Just note that if ACPI support is added to the sensor driver, you'll need
> the clock-frequency property again, for that's the only way how the driver
> will get the clock frequency.

Why is so ? Why can't we implement of assigned-clock-rates for ACPI ?

> This is certainly not something that has to be taken into account in DT
> bindings, but in any case it'll add some lines of code in the driver which
> are not very useful.

-- 
Regards,

Laurent Pinchart