Re: MAX1363 IIO driver questions

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Jan 29, 2013 at 09:10:25PM +0100, Lars-Peter Clausen wrote:
> On 01/29/2013 09:00 PM, Guenter Roeck wrote:
> > On Sat, Jan 26, 2013 at 11:25:35AM +0000, Jonathan Cameron wrote:
> >> On 01/18/2013 10:09 PM, Guenter Roeck wrote:
> >>> On Thu, Jan 17, 2013 at 09:03:58PM +0000, Jonathan Cameron wrote:
> >>>>
> >>>> Good point. New use case for us so suggestions on how to do the association cleanly would be most welcome. Is there anything similar out there? We could add a per iio device sysfs interface to add additional mappings but it is a little uggly...
> >>>>
> >>>
> >>> Best idea I can come up with is to disconnect iio_hwmon from the requirement to
> >>> instantiate it explicitly. There might be two sysfs entries - one to
> >>> attach it to a specific iio device, and one to attach it to individual channels
> >>> of an iio device. Similar like the new_device interface on i2c adapters, and
> >>> along the line of
> >>>
> >>> echo max1139 something > /sys/module/iio_hwmon/something_else
> >>
> >> We'll have to have something more specific or the common case of more than
> >> one instance of an adc will cause trouble.  Obviously this doesn't matter
> >> doing by adding the map from the IIO side.
> >>
> >>>
> >>> and/or
> >>>
> >>> echo max1139 something channel > /sys/module/iio_hwmon/something_else
> >>>
> >>> ie sysfs attributes associated with iio_hwmon, not with the iio device itself.
> >>>
> >> This will play havock with the way the internal mappings work.  Originally
> >> we had it mapped from both sides by name (e.g. the map wasn't in any way
> >> handled by either driver) but that got an awful lot of flack and really
> >> wasn't considered acceptable.  The current version of treating it much like
> >> regulators etc is much cleaner.
> >>
> > 
> > I think I am giving up on testing the code on a non-embedded system;
> > I would need/use manual instantiation only for testing, and it seems too
> > difficult to implement and not really worth it. I'll focus on getting it
> > to work with OF.
> > 
> > The current approach, with iio_hwmon requesting its assigned mappings through 
> > io_channel_get_all(), does not work well for me for a number of reasons.
> > 
> > First, it is difficult to associate device references in OF with actual device
> > names. I don't know if you have tried, but while a reference to &iio_hwmon can
> > uniquely identify the device name for an OF entry such as
> > 
> > 	iio_hwmon: iio_hwmon@0 {
> > 		compatible = "iio-hwmon";
> > 	};
> > 
> > it is difficult to predict how the actual iio_hwmon device name looks like.
> > Amongst others, it depends if there are additional attributes such as "reg = <>",
> > on the value of "@x" (if specified) and other attributes I have not really tracked
> > down yet. In other words, when I tried to create a device named "iio_hwmon.0",
> > I managed to get all kinds of device names except for "iio_hwmon.0".
> > 
> > Also, the iio_hwmon driver does not know which consumers are assigned to it.
> > If it is instantiated before the ADC driver (which happens all the time for me,
> > as iio_hwmon does not have to wait for the i2c bus adapter), its call to
> > iio_channel_get_all() returns nothing. Even if it does return some mappings,
> > there is no guarantee that the mappings are complete (eg if an instance of
> > iio_hwmon is mapped to ADC channels from multiple chips).
> > 
> > Other subsystems solve that problem by having the consumer request the resources
> > it needs. The leds-gpio driver is an excellent example: It knows from its OF data
> > which gpio pins it needs and requests those. If the pins are not available,
> > it gets an -EPROBE_DEFER error from the gpio subsystem, and simply defers
> > its probe until the missing pins are available.
> > 
> > The question for me is really if it would be possible to implement the same
> > approach for the iio subsystem. I would then specify something like
> > 
> > 	max1139: max1139@35 {
> >         	compatible = "maxim,max1139";
> > 		reg = <0x35>;
> > 	};
> > 
> > ...
> > 	iio_hwmon {
> > 		compatible = "iio-hwmon";
> > 
> > 		in0 {
> > 			label = "vin";
> > 			iio-map = { &max1139 0 }; /* adc channel 0 */
> > 		};
> > 		in1 {
> > 			label = "vout";
> > 			iio-map = { &max1139 1 }; /* adc channel 1 */
> > 		};
> > 		...
> > 	};
> > 
> > which would then map into in0/in1 hwmon attributes (with optional "vin" and
> > "vout" labels if specified).
> > 
> > Problem here is that io_channel_get() currently does not use the provider name
> > as argument to find the resource. Instead, it uses consumer_dev_name and/or
> > consumer_channel. I am not sure how to solve that problem. It would be much more
> > helpful if the provider would not be tied to the consumer from provider side,
> > but from consumer side, and the mapping would be based on provider device and
> > index (or something else such as ADC channel name if that is preferred).
> > 
> > Would this kind of solution be acceptable for the iio maintainers ? Is it
> > even possible, given that the provider has to currently provide the mapping
> > to its intended consumers using iio_map_array_register() ?
> 
> Hi Guenter,
> 
> I wrote in another mail a few days ago, how I think dt bindings for IIO could
> be implemented. The basic idea was to simply use bindings very similar to what
> the clk API uses, since its provider/consumer structure actually matches what
> we do in IIO pretty good.
> 
> The full mail can be found here:
> http://marc.info/?l=linux-iio&m=135902119507483&w=2
> 
Hi Lars,

looks like a good idea.

Do you know if anyone is working on an implementation ?
Otherwise I'll give it a shot.

Thanks,
Guenter