On 01/29/2013 10:05 PM, Guenter Roeck wrote:
> 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.
I unfortunately dont have time for this atm, but maybe Naveen or Dou is working
on it. Added them to Cc.
- Lars
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