Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module

From	Sylwester Nawrocki <snawrocki@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module
Date	2017-06-28 01:00 +0200
Message-ID	<tX7CG-71T-23@gated-at.bofh.it> (permalink)
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On 06/27/2017 07:48 AM, H. Nikolaus Schaller wrote:
>> Am 26.06.2017 um 22:04 schrieb Sylwester Nawrocki <snawrocki@kernel.org>:
>>
>> On 06/26/2017 12:35 PM, Hugues FRUCHET wrote:
>>>> What I am missing to support the GTA04 camera is the control of the optional "vana-supply".
>>>> So the driver does not power up the camera module when needed and therefore probing fails.
>>>>
>>>>     - vana-supply: a regulator to power up the camera module.
>>>>
>>>> Driver code is not complex to add:
>>
>>> Yes, I saw it in your code, but as I don't have any programmable power
>>> supply on my setup, I have not pushed this commit.
>>
>> Since you are about to add voltage supplies to the DT binding I'd suggest
>> to include all three voltage supplies of the sensor chip. Looking at the OV9650
>> and the OV9655 datasheet there are following names used for the voltage supply
>> pins:
>>
>> AVDD - Analog power supply,
>> DVDD - Power supply for digital core logic,
>> DOVDD - Digital power supply for I/O.
> 
> The latter two are usually not independently switchable from the SoC power
> the module is connected to.
> 
> And sometimes DVDD and DOVDD are connected together.
> 
> So the driver can't make much use of knowing or requesting them because the
> 1.8V supply is always active, even during suspend.
> 
>>
>> I doubt the sensor can work without any of these voltage supplies, thus
>> regulator_get_optional() should not be used. I would just use the regulator
>> bulk API to handle all three power supplies.
> 
> The digital part works with AVDD turned off. So the LDO supplying AVDD should
> be switchable to save power (&vaux3 on the GTA04 device).>
> But not all designs can switch it off. Hence the idea to define it as an
> /optional/ regulator. If it is not defined by DT, the driver simply assumes
> it is always powered on.

I didn't say we can't define regulator supply properties as optional in the DT 
binding.  If we define them as such and any of these *-supply properties is 
missing in DT with regulator_get() the regulator core will use dummy regulator 
for that particular voltage supply.  While with regulator_get_optional() 
-ENODEV is returned when the regulator cannot be found. 

> So in summary we only need AVDD switched for the GTA04 - but it does not
> matter if the others are optional properties. We would not use them.
> 
> It does matter if they are mandatory because it adds DT complexity (size
> and processing) without added function.
 
We should not be defining DT binding only with selected use cases/board
designs in mind.  IMO all three voltage supplies should be listed in the
binding, presumably all can be made optional, with an assumption that when
the property is missing selected pin is hooked up to a fixed regulator.

--
Thanks,
Sylwester

Thread

[PATCH v1 0/6] Add support of OV9655 camera Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
  [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
    Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 12:30 +0200
      Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Andreas Färber <afaerber@suse.de> - 2017-06-23 12:50 +0200
        Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 13:10 +0200
          Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-06-23 14:00 +0200
            Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 17:00 +0200
              Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Andreas Färber <afaerber@suse.de> - 2017-06-23 17:00 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 17:30 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Suman Anna <s-anna@ti.com> - 2017-06-23 20:10 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 21:10 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Suman Anna <s-anna@ti.com> - 2017-06-24 00:30 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 08:10 +0200
      Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-26 12:40 +0200
        Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Sylwester Nawrocki <snawrocki@kernel.org> - 2017-06-26 22:10 +0200
          Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-27 07:50 +0200
            Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Sylwester Nawrocki <snawrocki@kernel.org> - 2017-06-28 01:00 +0200
              Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-28 11:20 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera  module Sylwester Nawrocki <s.nawrocki@samsung.com> - 2017-06-28 13:00 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-28 13:30 +0200
                Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-28 14:30 +0200
      Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Rob Herring <robh@kernel.org> - 2017-06-26 21:00 +0200
    Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module Rob Herring <robh@kernel.org> - 2017-06-26 21:00 +0200
  [PATCH v1 2/6] [media] ov9650: add device tree support Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
    Re: [PATCH v1 2/6] [media] ov9650: add device tree support Sakari Ailus <sakari.ailus@iki.fi> - 2017-06-26 18:40 +0200
      Re: [PATCH v1 2/6] [media] ov9650: add device tree support "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 19:50 +0200
        Re: [PATCH v1 2/6] [media] ov9650: add device tree support Sakari Ailus <sakari.ailus@iki.fi> - 2017-06-27 07:40 +0200
          Re: [PATCH v1 2/6] [media] ov9650: add device tree support Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-27 12:20 +0200
  [PATCH v1 4/6] [media] ov9650: use write_array() for resolution sequences Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
    Re: [PATCH v1 4/6] [media] ov9650: use write_array() for resolution  sequences Sakari Ailus <sakari.ailus@iki.fi> - 2017-06-26 18:40 +0200
      Re: [PATCH v1 4/6] [media] ov9650: use write_array() for resolution  sequences Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-29 16:10 +0200
  [PATCH v1 3/6] [media] ov9650: select the nearest higher resolution Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
  [PATCH v1 6/6] [media] ov9650: add support of OV9655 variant Hugues Fruchet <hugues.fruchet@st.com> - 2017-06-22 17:10 +0200
    Re: [PATCH v1 6/6] [media] ov9650: add support of OV9655 variant kbuild test robot <lkp@intel.com> - 2017-06-25 18:10 +0200
    [PATCH] ov9650: fix semicolon.cocci warnings kbuild test robot <lkp@intel.com> - 2017-06-25 18:10 +0200
    Re: [PATCH v1 6/6] [media] ov9650: add support of OV9655 variant "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 08:10 +0200
  Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-22 17:50 +0200
    Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-23 12:30 +0200
      omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655 camera Pavel Machek <pavel@ucw.cz> - 2017-06-25 11:20 +0200
        Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 08:10 +0200
          Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655  camera Pavel Machek <pavel@ucw.cz> - 2017-06-26 10:40 +0200
            Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 12:00 +0200
              Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655  camera Pavel Machek <pavel@ucw.cz> - 2017-06-26 13:20 +0200
                Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-27 08:00 +0200
            Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655  camera Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-26 15:30 +0200
              Re: omap3isp camera was Re: [PATCH v1 0/6] Add support of OV9655  camera Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-27 10:00 +0200
                Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-07-01 23:10 +0200
                Re: [PATCH v1 0/6] Add support of OV9655 camera Hugues FRUCHET <hugues.fruchet@st.com> - 2017-07-03 10:20 +0200
                Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-07-03 11:20 +0200
                Re: [PATCH v1 0/6] Add support of OV9655 camera Hugues FRUCHET <hugues.fruchet@st.com> - 2017-07-03 14:10 +0200
                Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-07-03 14:30 +0200
      Re: [PATCH v1 0/6] Add support of OV9655 camera "H. Nikolaus Schaller" <hns@goldelico.com> - 2017-06-26 08:10 +0200
    Re: [PATCH v1 0/6] Add support of OV9655 camera Hugues FRUCHET <hugues.fruchet@st.com> - 2017-06-26 12:10 +0200

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