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

Laurent Pinchart
2019-10-31T16:54:55Z

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@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.
>
> 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