On 3/6/19 9:17 AM, Harald Geyer wrote: > Marek Vasut writes: >> On 3/5/19 10:36 PM, Harald Geyer wrote: >>> Marek Vasut writes: >>>> On 3/5/19 5:10 PM, Harald Geyer wrote: >>>>> Marek Vasut writes: >>>>>> On 3/5/19 11:07 AM, Harald Geyer wrote: >>>>>>> marek.vasut@xxxxxxxxx writes: >>>>>>>> From: Marek Vasut <marek.vasut+renesas@xxxxxxxxx> >>>>>>>> >>>>>>>> Reword the binding document to make it clear how the propeties work >>>>>>>> and which properties affect which other properties. >>>>>>>> >>>>>>>> Signed-off-by: Marek Vasut <marek.vasut+renesas@xxxxxxxxx> >>>>>>>> Cc: Harald Geyer <harald@xxxxxxxxx> >>>>>>>> Cc: Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx> >>>>>>>> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx> >>>>>>>> Cc: Mark Brown <broonie@xxxxxxxxxx> >>>>>>>> Cc: Rob Herring <robh@xxxxxxxxxx> >>>>>>>> Cc: linux-renesas-soc@xxxxxxxxxxxxxxx >>>>>>>> To: devicetree@xxxxxxxxxxxxxxx >>>>>>>> --- >>>>>>>> V2: - Make "gpios" a mandatory property >>>>>>>> - Reword "gpio-states" property description >>>>>>>> - Change "enable-gpio" to "enable-gpios" to match modern DT rules >>>>>>>> Note: The recent gpio-regulator rework caused breakage. While the >>>>>>>> changes in the gpio-regulator code were according to the DT >>>>>>>> binding document, they stopped working with older DTs. Make >>>>>>>> the binding document clearer to prevent such breakage in the >>>>>>>> future. >>>>>>> >>>>>>> Thanks for the update. I think it addresses all my concerns except for >>>>>>> one: >>>>>>> >>>>>>>> +- gpios-states : State of GPIO pins in "gpios" array that is set until >>>>>>>> + changed by the first consumer. 0: LOW, 1: HIGH. >>>>>>>> + Default is LOW if nothing else is specified. >>>>>>> >>>>>>> I still believe this not true: There is no guarantee that the regulator >>>>>>> core won't change the state of GPIO pins before the first consumer comes >>>>>>> up. >>>>>> >>>>>> Why would it do that ? >>>>> >>>>> Because the regulator core doesn't know about this driver specific >>>>> property at all. And without any constraints placed by consumers, the >>>>> core is free to choose any state whatsoever at any point in time. >>>> >>>> But git grep seems to disagree, see drivers/regulator/gpio-regulator.c: >>>> ret = of_property_read_u32_index(np, "gpios-states", i, >>>> >>>> The core sets the pins to such a value until the consumer takes over. >>> >>> I think we have a misunderstanding of terminology. When I write "regulator >>> core", I mean the driver independent regulator code. The line you quote >>> above is part of the gpio-regulator driver and thus not part of what >>> I call the "regulator core". >>> >>> AFAICS the data from the property is only stored in a driver specific >>> data structure (and not used at all outside of probe) but never passed >>> to what I call the regulator core. >>> >>> Why do you believe there is a guarantee that the value set during >>> probeing is preserved until a consumer takes over? >> >> It is the only sensible behavior and the behavior I see people expect >> from this property. I presume it solidified in this sort of semi-defined >> state, so we're stuck with assuming it behaves this way to maintain >> compatibility. > > Maybe the behaviour you want would be more sensible, but AFAIK it just > isn't true in general (it might work that way by chance in many cases). > If people expect this behaviour, it is a misunderstanding of the old wording. > I'd prefer we don't have to add a quirk to the regulator subsystem to > cater for a misunderstanding. > > I think, if you really want to go forward with making this behaviour > officially maintained, then we should first add the code to linux and > only then add the promise to the binding document. This isn't the scope > of this patch, so I guess we would need to keep the ambiguous wording as > it is for now. I believe it is more important for a binding document > to be correct than to be sensible. > > However I don't think we actually need to go to such extremes: In linux > we currently have (arm/boot/dts and arm64/boot/dts) 38 uses of this > property in 29 DTs. All the examples, that I studied in some detail, > seem to either don't need this property at all or have a usecase that is > supported by my proposed wording. I don't expect any problems if we just > document the status quo clearly. In that case, provide a suggestion how to document this property better? -- Best regards, Marek Vasut
