On Wed, 2011-04-13 at 14:22 +0200, Michael Hennerich wrote: > On 04/12/2011 05:21 PM, Mark Brown wrote: > > On Tue, Apr 12, 2011 at 12:08:22PM +0100, Hennerich, Michael wrote: > > > > Please fix your mail client to word wrap at less than 80 columns - see > > Documentation/email-clients.txt for suggestions. I've reflowed your > > text for legibility. > > > > > >> I wonder why the voltage and current regulator framework doesn't > >> support negative voltages. We like to use the framework to specify > >> bipolar reference voltages used with converters. However in various > >> places negative voltages are treated as error codes, thus causing the > >> regulator to exit on probe. > >> > > Basically just a lack of demand - there are few negative supplies in > > the mobile systems that were looked at, and most of those are like the > > charge pumps found in audio CODECs and not really visible as regulators > > that could be used with other devices. > > > > Hi Mark, > > Contrast control for LC Displays typically use negative voltages, too > I agree that demand for this on typical mobile devices is low, however > we like > to use the regulator framework in the IIO subsystem where negative voltages > are quite common. > > > >> As a workaround someone could say we specify positive and negative > >> supply by label with absolute values and add the negative sign in the > >> consumer driver. However that doesn't work well, since the bipolar > >> 'negative' supply may also occasionally be positive. > >> > > That'd probably work. Or update the API to allow negative voltages to > > be returned more easily; off the top of my head the only real issue is > > get_voltage() and so on. It'd not be great for usability, though. > > > Updating the core to allow negative and zero voltages, is not straight > forward. > There are more issues with constrain checking and I currently can't > oversee all side The voltage constraints are just treated as numbers so negative constraints for bipolar regulators should be fine here. I don't anticipate lots of rework here. There is also some core logic that selects the lowest voltage within a range of valid voltages (to save power) when consumers set a voltage. This would need changed a little to support negative voltages since the lowest voltage will be the _highest_ negative voltage. > effects. I think we need to introduce a new constrains flag > (maybe add to valid_modes_mask?), indicating a bipolar regulator. > This flag is then used to keep the current implementation untouched for > unipolar positive > regulators. > > Thoughts? > My preference is to keep it simple and the API consistent with unipolar regulators. One of the problem areas will be regulator_get_voltage() since it returns negative errors. It may be desirable to deprecate this API call in favour of a new call that we pass in an int for the voltage (e.g. get_voltage(reg, &voltage)). Lets also hear what Mark's thoughts too. Regards Liam -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
