Re: [V7, 1/2] media: dt-bindings: media: i2c: Document OV02A10 bindings

[Tomasz Figa <tfiga@chromium.org>]

On Thu, May 7, 2020 at 4:12 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> Hi Tomasz, Dongchun,
>
> On Thu, May 07, 2020 at 03:50:40PM +0200, Tomasz Figa wrote:
> > Hi Sakari and Dongchun,
> >
> > On Thu, May 7, 2020 at 3:00 PM Dongchun Zhu <dongchun.zhu@mediatek.com> wrote:
> > >
> > > Hi Sakari,
> > >
> > > Thanks for the review.
> > >
> > > On Wed, 2020-05-06 at 14:21 +0300, Sakari Ailus wrote:
> > > > Hi Dongchun,
> > > >
> > > > On Tue, May 05, 2020 at 10:17:18PM +0800, Dongchun Zhu wrote:
> > > > > Hi Sakari,
> > > > >
> > > > > Thanks for the review.
> > > > >
> > > > > On Tue, 2020-05-05 at 10:04 +0300, Sakari Ailus wrote:
> > > > > > Hi Dongchun,
> > > > > >
> > > > > > On Thu, Apr 30, 2020 at 04:09:23PM +0800, Dongchun Zhu wrote:
> > > > > > > Add DT bindings documentation for Omnivision OV02A10 image sensor.
> > > > > > >
> > > > > > > Signed-off-by: Dongchun Zhu <dongchun.zhu@mediatek.com>
> > > > > > > ---
> > > > > > >  .../bindings/media/i2c/ovti,ov02a10.yaml           | 148 +++++++++++++++++++++
> > > > > > >  MAINTAINERS                                        |   7 +
> > > > > > >  2 files changed, 155 insertions(+)
> > > > > > >  create mode 100644 Documentation/devicetree/bindings/media/i2c/ovti,ov02a10.yaml
> > > > > > >
> > > > > > > diff --git a/Documentation/devicetree/bindings/media/i2c/ovti,ov02a10.yaml b/Documentation/devicetree/bindings/media/i2c/ovti,ov02a10.yaml
> > > > > > > new file mode 100644
> > > > > > > index 0000000..2be4bd2
> > > > > > > --- /dev/null
> > > > > > > +++ b/Documentation/devicetree/bindings/media/i2c/ovti,ov02a10.yaml
> > > > > > > @@ -0,0 +1,148 @@
> > > > > > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > > > > > +# Copyright (c) 2020 MediaTek Inc.
> > > > > > > +%YAML 1.2
> > > > > > > +---
> > > > > > > +$id: http://devicetree.org/schemas/media/i2c/ovti,ov02a10.yaml#
> > > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > > +
> > > > > > > +title: Omnivision OV02A10 CMOS Sensor Device Tree Bindings
> > > > > > > +
> > > > > > > +maintainers:
> > > > > > > +  - Dongchun Zhu <dongchun.zhu@mediatek.com>
> > > > > > > +
> > > > > > > +description: |-
> > > > > > > +  The Omnivision OV02A10 is a low-cost, high performance, 1/5-inch, 2 megapixel
> > > > > > > +  image sensor, which is the latest production derived from Omnivision's CMOS
> > > > > > > +  image sensor technology. Ihis chip supports high frame rate speeds up to 30fps
> > > > > > > +  @ 1600x1200 (UXGA) resolution transferred over a 1-lane MIPI interface. The
> > > > > > > +  sensor output is available via CSI-2 serial data output.
> > > > > > > +
> > > > > > > +properties:
> > > > > > > +  compatible:
> > > > > > > +    const: ovti,ov02a10
> > > > > > > +
> > > > > > > +  reg:
> > > > > > > +    maxItems: 1
> > > > > > > +
> > > > > > > +  clocks:
> > > > > > > +    items:
> > > > > > > +      - description: top mux camtg clock
> > > > > > > +      - description: devider clock
> > > > > > > +
> > > > > > > +  clock-names:
> > > > > > > +    items:
> > > > > > > +      - const: eclk
> > > > > > > +      - const: freq_mux
> > > > > > > +
> > > > > > > +  clock-frequency:
> > > > > > > +    description:
> > > > > > > +      Frequency of the eclk clock in Hertz.
> > > > > > > +
> > > > > > > +  dovdd-supply:
> > > > > > > +    description:
> > > > > > > +      Definition of the regulator used as interface power supply.
> > > > > > > +
> > > > > > > +  avdd-supply:
> > > > > > > +    description:
> > > > > > > +      Definition of the regulator used as analog power supply.
> > > > > > > +
> > > > > > > +  dvdd-supply:
> > > > > > > +    description:
> > > > > > > +      Definition of the regulator used as digital power supply.
> > > > > > > +
> > > > > > > +  powerdown-gpios:
> > > > > > > +    description:
> > > > > > > +      The phandle and specifier for the GPIO that controls sensor powerdown.
> > > > > > > +
> > > > > > > +  reset-gpios:
> > > > > > > +    description:
> > > > > > > +      The phandle and specifier for the GPIO that controls sensor reset.
> > > > > > > +
> > > > > > > +  rotation:
> > > > > > > +    description:
> > > > > > > +      Definition of the sensor's placement, valid values are 0 and 180.
> > > > > > > +    allOf:
> > > > > > > +      - $ref: "/schemas/types.yaml#/definitions/uint32"
> > > > > > > +      - enum:
> > > > > > > +          - 0    # Sensor Mounted Upright
> > > > > > > +          - 180  # Sensor Mounted Upside Down
> > > > > > > +
> > > > > > > +  ovti,mipi-tx-speed:
> > > > > > > +    description:
> > > > > > > +      Indication of MIPI transmission speed select.
> > > > > >
> > > > > > What exactly does this signify? And how do you come up with the number?
> > > > > >
> > > > >
> > > > > Apologies for not addressing this number clear.
> > > > >
> > > > > From the datasheet, P1:0xA1 register represents TX_SPEED_AREA_SEL with
> > > > > the default val: 0x03.
> > > > > The description of this RW register is as below:
> > > > > Bit[2:0]: MIPI transmission speed select.
> > > > >
> > > > > Thus the enum should be definited as [ 0, 1, 2, 3, 4, 5, 6, 7 ].
> > > > > This would be fixed in next release.
> > > > >
> > > > > In the meantime, as the default val of P1:0xA1 is 0x03, we hope to keep
> > > > > that value if there is no setting for this private property in DT.
> > > > > The caller in driver would be updated like this in next release.
> > > > > if (ov02a10->mipi_clock_tx_speed)
> > > > >     ret = i2c_smbus_write_byte_data(...,...);
> > > >
> > > > How did you pick the value in the example? And why do you believe it is
> > > > specific to a platform, and not e.g. a sensor mode?
> > > >
> > >
> > > We look into P1:0XA1, one register that defines MIPI transmission speed
> > > select.
> > > From the datasheet, we can get the possible values that could be set to
> > > P1:0xA1.
> > >
> > > Actually this register is an independent of sensor mode, it is just
> > > included in sensor mode's register setting table.
> > >
> > > In addition, this private DT Property is created to fix the MIPI test
> > > failure. The register values are adjusted and verified from vendor to
> > > make sensor signal meet MIPI specification.
> > >
> >
> > In theory the value could depend on the mode, because different link
> > rate could impose different requirements for the physical interface.
> > In practice, we haven't seen any hardware that would require different
> > values for different modes.
>
> The mode (possibly in conjunction with other information available to the
> driver via V4L2 fwnode interface) precisely defines the parameters of the
> CSI-2 bus --- apart from the possible exception of the bus timing related
> parameters but this is not supported by the name of the parameter.
>
> Therefore I don't see how this parameter, which supposedly is used to
> determine the CSI-2 transmissions speed, could be board specific and thus
> belong to DT.

According to the very imprecise information I have access to, it is
not about the CSI-2 bus itself, but rather some internal parameter of
the sensor's CSI interface. Unfortunately there isn't much information
on what this value exactly controls...

Best regards,
Tomasz