Hello Tim, On 08/15/2014 07:36 AM, Tim Kryger wrote: > On Thu, Aug 14, 2014 at 8:19 AM, Mark Brown <broonie@xxxxxxxxxx> wrote: > >> Right, there's two things going on here. One is that as you describe we >> shouldn't be putting constraints in .dtsi files if we don't know they're >> OK for a given board. The other thing is that on this particular board >> it turns out that there's no support for varying the voltages at all so >> it doesn't make sense to have to specify a range, there's only one value >> anyway so the software really should be able to figure out that fixed >> value all by itself. > > If constraints are truly irrelevant when the voltage supplied to > consumers is fixed, why doesn't regulator_list_voltage honor this > exemption and skip the voltage filtering that uses (potentially > unspecified) constraints when output is entirely determined by a > parent (or grandparent) supply that can't change its voltage? > I had a similar thought before and proposed the patch: "[RFC 3/5] regulator: core: Only apply constraints if available on list voltage" [0]. But then Mark explained to me that this is wrong since in that case regulator_list_voltage() will list voltages that can't really be set [1]. But now I wonder why regulator_list_voltage() even list the voltage for fixed regulators (desc->fixed_uV) since they don't have the ability to vary voltage. The regulator_list_voltage() documentation says: "Returns a voltage that can be passed to @regulator_set_voltage(), zero if this selector code can't be used on this system, or a negative errno." But in the case of fixed regulators, it is actually listing a voltage that can't be selected. Although regulator_set_voltage() checks if the desired voltage is equal to the regulator min_uV and max_uV and just exits in that case, it feels wrong to list the voltage for a fixed regulators. regulator_list_voltage() only works because of the way we define the generic fixed voltage regulators and that is assuming that "regulator-min-microvolt" and "regulator-max-microvolt" DT properties being the same means that the regulator is fixed. This is kind of unfortunate, maybe it would had been better to define it explicitly using a "regulator-fixed-microvolt" or something. If we had such a DT property, then constraints wouldn't had been set for fixed regulators and regulator_list_voltage() wouldn't list its voltage neither. > It seems odd to make callers be the ones to handle this subtlety. > If regulator_list_voltage() didn't list the voltage for fixed regulators, then this subtlety should had been handled by callers before but they didn't because they rely on regulator_list_voltage() to always return a voltage even for fixed regulators. > Thanks, > Tim Kryger > Best regards, Javier [0]: https://lkml.org/lkml/2014/7/29/418 [1]: https://lkml.org/lkml/2014/7/29/453 -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
