On Fri, Aug 29, 2014 at 11:40:02AM +0100, Mark Rutland wrote: > On Fri, Aug 29, 2014 at 08:34:25AM +0100, Matti Vaittinen wrote: > > On Thu, Aug 28, 2014 at 10:40:34AM -0700, ext Guenter Roeck wrote: > > > On Thu, Aug 28, 2014 at 01:28:42PM -0400, Jason Cooper wrote: > > > > On Thu, Aug 28, 2014 at 09:48:25AM -0700, Guenter Roeck wrote: > > > > > On Thu, Aug 28, 2014 at 05:10:25PM +0100, Mark Rutland wrote: > > > > > > On Thu, Aug 28, 2014 at 04:51:57PM +0100, Guenter Roeck wrote: > > > > > > > On Thu, Aug 28, 2014 at 01:59:15PM +0100, Mark Rutland wrote: > > > > > > > > On Thu, Aug 28, 2014 at 01:42:44PM +0100, Matti Vaittinen wrote: > > > > > > > > > Patch adding support for specifying trickle charger setup from device > > > > > > > > > tree. Patch is based on linux-next tree. > > > > > > > > > > > > > > > > > > > > > > > > > > > Some DS13XX devices have "trickle chargers". Introduce a device tree binding > > > > > > > > > for specifying the setup and register values. > > > > > > > > > > > > > > > > > > +++ b/Documentation/devicetree/bindings/rtc/dallas,ds1339.txt > > > > > > > > > @@ -0,0 +1,19 @@ > > > > > > > > > +* Dallas DS1339 I2C Serial Real-Time Clock > > > > > > > > > + > > > > > > > > > +Required properties: > > > > > > > > > +- compatible: Should contain "dallas,ds1339". > > > > > > > > > +- reg: I2C address for chip > > > > > > > > > + > > > > > > > > > +Optional properties: > > > > > > > > > +- trickle_setup : Used Trickle Charger configuration, > > > > > > > > > + corresponding to 5 lowest bits in trickle charger register. > > > > > > > > > > > > > > > The value is provided via platform data, so it is platform specific > > > > > > > and presumably needs to be configurable. I did, however, not find > > > > > > > a single in-kernel driver which is actually setting it. > > > > > > > So this is a good question. > > > > > > > > > > > > I'm uncomfortable adding a field we don't understand to DT. > > > > > > > > > > > > Is there any publicly-available documentation for the device? > > > > > > > > > > > > > > > > Lots ;-) > > > > > > > > > > http://datasheets.maximintegrated.com/en/ds/DS1307.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS1337.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS1338.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS1339.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS1340.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS1388.pdf > > > > > http://datasheets.maximintegrated.com/en/ds/DS3231.pdf > > > > > > > > > > Code suggests that DS1339, DS1339, and DS1340 have the register. > > > > > > > > > > Looking into the datasheets, the configuration consists of two parts: > > > > > - diode connected or not > > > > > - trickle charger resistor value (250, 2000, or 4000 ohm) > > > > > > > > > > Given that, it seems to me that those values should be configured > > > > > explicitly instead of using a binary value, and that the driver > > > > > should perform the conversion from dt entry to register value. > > > > > > > > iiuc, there is no way for the kernel to determine what is being trickle > > > > charged, and thus no way to determine how it should set this register. > > > > > > > > It may be a bit of overkill, but I think a DT macro would be the most > > > > maintainable solution here: > > > > > > > > #define DS1339_TRCKL_DIODE 0x08 > > > > #define DS1339_TRCKL_NODIODE 0x04 > > > > #define DS1339_TRCKL_R250 0x01 > > > > #define DS1339_TRCKL_R2000 0x02 > > > > #define DS1339_TRCKL_R4000 0x03 > > > > > > > > trickle_setup = <DS1339_TRCKL_DIODE | DS1339_TRCKL_R250>; > > > > > > > > And the driver would take care of oring it with the enable pattern. > > > > > > > > > > Yes, that sounds reasonable as well. > > > > > I thought of this too. However the ds1307 seems to be designed to work > > with bunch of chips. What then when next chip supported by this driver > > introduces 75, 1000 and 5000 ohm resistors? Or something else. (Or add > > some other configuration). I do not see this approach to be > > maintainable in long run. > > If a new chip comes out with new features, the driver will need an > update anyhow. We have no guarantee that the register placement will be > the same, let alone the layout. Yes, I'm reminded of our conversations a year ago in Edinburgh. It's impossible to engineer a perfect, future-proof binding. But that being said... > If and when said new chip comes out we allocate a new compatible string. > If it's compatible iwith (i.e. is a superset of) an existing device's > programming model, we add that existing string as a fallback in the > compatible list so old kernels can drive the subset of features they > understand. > > > I see strong possibility of polluting dt with endless amount of > > defines. Furthermore I believe the benefits of these defines would be > > negligible compared to effort maintaining defines and documentation of > > them causes. Surely the one who needs to add dt node for this chip in > > his board's dt has the manual for the chip he has on board. Especially > > so if he knows the trickle charger there and wants to configure it. > > The plain resistor type still gives zero information without knowing > > the other details. > > I would rather that the driver had some idea of what it were doing > rather than being a glorified copy routine. > > I would suggest we have two properties that describe the resistor's > rating and whether or not there is a diode: > > trickle-resistor-ohms = <250> > diode-connected; I much prefer this solution over my own suggestion. With one small change, s/diode-connected/trickle-diode-enable/ Does that sound ok? > That's easy for a human to write and/or validate, we can easily extend > it in future, requires no proliferation of macros, and describes the > hardware rather than telling software what to do. > > The driver becomes a little more complicated, but gains sanity checking, > which is a good thing. > > I'm still worried that we have no idea what the device is intended to > charge. Surely that's important? In the docs it said a variety of batteries and supercaps. Yeah, not much help... thx, Jason. -- 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
