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

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Message-ID: <2d916065-fd81-6f52-5d32-a46331e0c5ed@st.com>
Date:   Wed, 28 Jun 2017 12:28:31 +0000
From:   Hugues FRUCHET <hugues.fruchet@...com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>
CC:     Guennadi Liakhovetski <g.liakhovetski@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module



On 06/28/2017 01:24 PM, H. Nikolaus Schaller wrote:
> 
>> Am 28.06.2017 um 12:50 schrieb Sylwester Nawrocki <s.nawrocki@...sung.com>:
>>
>> On 06/28/2017 11:12 AM, H. Nikolaus Schaller wrote:
>>>> Am 28.06.2017 um 00:57 schrieb Sylwester Nawrocki <snawrocki@...nel.org>:
>>>> On 06/27/2017 07:48 AM, H. Nikolaus Schaller wrote:
>>>>>> Am 26.06.2017 um 22:04 schrieb Sylwester Nawrocki <snawrocki@...nel.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.
>>
>> Indeed, this commit explains it further:
>>
>> commit de1dd9fd2156874b45803299b3b27e65d5defdd9
>> regulator: core: Provide hints to the core about optional supplies
>>
>>> 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?
>>
>> Yes, I think so. So we have a possibly complete binding right from the
>> beginning. I someone needs handling other supplies than AVDD they could
>> update the driver in future.
> 
> Fine! I have sent some patches to Hughues so that he can integrate it in
> his next version of the patch series.
> 
> BR and thanks,
> Nikolaus
> 

OK got it, I'll push in v2.