On 06/28/2017 11:12 AM, H. Nikolaus Schaller wrote: >> Am 28.06.2017 um 00:57 schrieb Sylwester Nawrocki <snawrocki@xxxxxxxxxx>: >> On 06/27/2017 07:48 AM, H. Nikolaus Schaller wrote: >>>> Am 26.06.2017 um 22:04 schrieb Sylwester Nawrocki <snawrocki@xxxxxxxxxx>: >>>> 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. Regards, Sylwester -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
