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    SubjectRe: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module
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    > Am 28.06.2017 um 00:57 schrieb Sylwester Nawrocki <snawrocki@kernel.org>:
    >
    > 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.

    Ah, ok. I see.

    I had thought that it is the right thing to do like devm_gpiod_get_optional().

    That one it is described as:

    "* This is equivalent to gpiod_get(), except that when no GPIO was assigned to
    * the requested function it will return NULL. This is convenient for drivers
    * that need to handle optional GPIOs."

    Seems to be inconsistent definition of what "optional" means.

    So we indeed should use devm_regulator_get() in this case. Thanks for pointing out!

    >
    >> 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.

    Ok, then it should just be defined in the bindings but not used by the driver?

    BR and thanks,
    Nikolaus


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