Re: [PATCH v13 1/2] media: dt-bindings: media: i2c: Document OV02A10 bindings

Sakari Ailus
2020-09-01T16:18:02Z

On Tue, Sep 01, 2020 at 10:35:37PM +0800, Dongchun Zhu wrote:
> Hi Tomasz, Sakari,
>
> Thanks for digging into the imperfections.
>
> On Mon, 2020-08-31 at 19:06 +0300, Sakari Ailus wrote:
> > Hi Tomasz,
> >
> > Thanks for dressing this into words.
> >
> > On Mon, Aug 31, 2020 at 01:44:27PM +0200, Tomasz Figa wrote:
> > > Hi Dongchun,
> > >
> > > On Fri, Jul 10, 2020 at 12:19 PM Dongchun Zhu <dongchun.zhu@mediatek.com> wrote:
> > > >
> > > > Add YAML device tree binding for OV02A10 CMOS image sensor,
> > > > and the relevant MAINTAINERS entries.
> > > >
> > > > Reviewed-by: Tomasz Figa <tfiga@chromium.org>
> > > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > > Signed-off-by: Dongchun Zhu <dongchun.zhu@mediatek.com>
> > > > ---
> > > > .../bindings/media/i2c/ovti,ov02a10.yaml | 172 +++++++++++++++++++++
> > > > MAINTAINERS | 7 +
> > > > 2 files changed, 179 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..3a916cc
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/media/i2c/ovti,ov02a10.yaml
> > > > @@ -0,0 +1,172 @@
> > > > +# 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: divider clock
> > > > +
> > > > + clock-names:
> > > > + items:
> > > > + - const: eclk
> > > > + - const: freq_mux
> > >
> > > Why do we have two clocks here? Looking at the example suggests that
> > > they may be the clocks of the SoC that the integration was done with.
> > > However, the binding must only define the aspects of the particular
> > > device, i.e. this sensor.
> > >
> > > I suppose we should only have "eclk" here and it should be described
> > > as "external clock for the sensor".
> > >
>
> I cannot agree with you more, it would be fixed in next release.
>
> > > > +
> > > > + clock-frequency:
> > > > + description:
> > > > + Frequency of the eclk clock in Hertz.
> > >
> > > nit: maybe Hz?
> > >
>
> Both shall be okay, let's use Hz instead, which seems to be more simple.
>
> > > > +
> > > > + dovdd-supply:
> > > > + description:
> > > > + Definition of the regulator used as Digital I/O voltage supply.
> > > > +
> > > > + avdd-supply:
> > > > + description:
> > > > + Definition of the regulator used as Analog voltage supply.
> > > > +
> > > > + dvdd-supply:
> > > > + description:
> > > > + Definition of the regulator used as Digital core voltage supply.
> > > > +
> > > > + powerdown-gpios:
> > > > + description:
> > > > + Must be the device tree identifier of the GPIO connected to the
> > > > + PD_PAD pin. This pin is used to place the OV02A10 into standby mode
> > > > + or shutdown mode. As the line needs to be high for the powerdown mode
> > > > + to be active, it should be marked GPIO_ACTIVE_HIGH.
> > > > + maxItems: 1
> > > > +
> > > > + reset-gpios:
> > > > + description:
> > > > + Must be the device tree identifier of the GPIO connected to the
> > > > + RST_PD pin. If specified, it will be asserted during driver probe.
> > > > + As the line needs to be low for the reset to be active, it should be
> > > > + marked GPIO_ACTIVE_LOW.
> > > > + maxItems: 1
> > > > +
> > > > + rotation:
> > > > + description:
> > > > + Definition of the sensor's placement.
> > > > + allOf:
> > > > + - $ref: "/schemas/types.yaml#/definitions/uint32"
> > > > + - enum:
> > > > + - 0 # Sensor Mounted Upright
> > > > + - 180 # Sensor Mounted Upside Down
> > > > + default: 0
> > > > +
> > > > + ovti,mipi-tx-speed:
> > > > + description:
> > > > + Indication of MIPI transmission speed select, which is to control D-PHY
> > > > + timing setting by adjusting MIPI clock voltage to improve the clock
> > > > + driver capability.
> > >
> > > The description says that the value adjusts "MIPI clock voltage".
> > > Should the property be renamed to "ovti,mipi-clock-voltage"?
> > >
>
> Sure, mipi-clock-voltage seems more clear, perfect naming :-)
>
> > > > + allOf:
> > > > + - $ref: "/schemas/types.yaml#/definitions/uint32"
> > > > + - enum:
> > > > + - 0 # 20MHz - 30MHz
> > > > + - 1 # 30MHz - 50MHz
> > > > + - 2 # 50MHz - 75MHz
> > > > + - 3 # 75MHz - 100MHz
> > > > + - 4 # 100MHz - 130MHz
> > > > + default: 3
> > > > +
> > >
> > > I've discussed this on IRC with Sakari. It sounds like this works as
> > > is for us because the driver currently only supports 1 mode, always
> > > running the link at 390 MHz. This won't scale if one intends to add
> > > more modes, because DT can't be expected to be updated when the driver
> > > changes. The two are expected to be separate and backwards compatible.
> > >
> > > I think we could model this in DT as an array of <link speed, clock
> > > voltage> pairs. Similarly to the OPP bindings [1]. An example to have
> > > all link speeds up to 390 MHz use the value 4:
> > >
> > > ovti,mipi-clock-voltages = <
> > > /* KHz clock voltage unit */
> > > 390000 4
> > > >;
> > >
> > > if one wants to select different voltage for different link, they
> > > could do so as well. With the example below, the driver should
> > > configure "3" for link frequencies <= 150 MHz and "4" for > 150 MHz <=
> > > 390 MHz. Link frequencies > 390 MHz should be disallowed.
> > >
> > > ovti,mipi-clock-voltages = <
> > > /* KHz clock voltage unit */
> > > 150000 3
> > > 390000 4
> > > >;
> > >
> > > What do you think?
> >
>
> So now we define the MIPI clock voltage (unit) as one function of link
> frequency?
>
> For current sensor mode (1600x1200, 390MHz link frequency), we then
> shall always use the value 4 to configure the MIPI transmission speed
> selection (P1:0xA1). Am I correct in thinking that?
>
> > One more note on my proposal: use the index of the link frequency to access
> > the ovti,mipi-clock-voltages array. That should be more simple for the
> > driver, as the driver is expected to use only link frequencies listed in DT
> > bindings anyway.
> >
>
> Good idea! That's exactly what I mean.
> Just submitted one draft change to handle the new property in DT.
> @Sakari @Tomasz please help to review it.
> https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2387980/1/drivers/media/i2c/ov02a10.c#883

Please send it to the list.

--
Sakari Ailus