Re: [PATCH v2 4/4] iio: Add OF support

[Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>]

On 02/03/2013 06:30 PM, Tomasz Figa wrote:
> On Sunday 03 of February 2013 09:01:07 Guenter Roeck wrote:
>> On Sun, Feb 03, 2013 at 12:52:40PM +0100, Tomasz Figa wrote:
>>> On Sunday 03 of February 2013 12:29:23 Lars-Peter Clausen wrote:
>>>> On 02/03/2013 03:06 AM, Guenter Roeck wrote:
>>>>> On Sun, Feb 03, 2013 at 02:30:24AM +0100, Tomasz Figa wrote:
>>>>>> Hi Guenter,
>>>>>>
>>>>>> Some comments inline.
>>>>>>
>>>>>> On Saturday 02 of February 2013 16:59:40 Guenter Roeck wrote:
>>>>>>> Provide bindings and parse OF data during initialization.
>>>>>>>
>>>>>>> Signed-off-by: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
>>>>>>> ---
>>>>>>> - Documentation update per feedback
>>>>>>> - Dropped io-channel-output-names from the bindings document.
>>>>>>> The
>>>>>>> property is not used in the code, and it is not entirely clear
>>>>>>> what
>>>>>>> it
>>>>>>> would be used for. If there is a need for it, we can add it back
>>>>>>> in
>>>>>>> later on.
>>>>>>> - Don't export OF specific API calls
>>>>>>> - For OF support, no longer depend on iio_map
>>>>>>> - Add #ifdef CONFIG_OF where appropriate, and ensure that the
>>>>>>> code
>>>>>>> still builds if it is not selected.
>>>>>>> - Change iio_channel_get to take device pointer as argument
>>>>>>> instead
>>>>>>> of
>>>>>>> device name. Retain old API as of_iio_channel_get_sys.
>>>>>>> - iio_channel_get now works for both OF and non-OF
>>>>>>> configurations.
>>>>>>>
>>>>>>>  .../devicetree/bindings/iio/iio-bindings.txt       |   76
>>>>>>>  ++++++++
>>>>>>>  drivers/iio/inkern.c                               |  186
>>>>>>>
>>>>>>> ++++++++++++++++++++ 2 files changed, 262 insertions(+)
>>>>>>>
>>>>>>>  create mode 100644
>>>>>>>
>>>>>>> Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>>>>
>>>>>>> diff --git
>>>>>>> a/Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>>>> b/Documentation/devicetree/bindings/iio/iio-bindings.txt new
>>>>>>> file
>>>>>>> mode
>>>>>>> 100644
>>>>>>> index 0000000..58df5f6
>>>>>>> --- /dev/null
>>>>>>> +++ b/Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>>>> @@ -0,0 +1,76 @@
>>>>>>> +This binding is a work-in-progress. It is derived from clock
>>>>>>> bindings,
>>>>>>> +and based on suggestions from Lars-Peter Clausen [1].
>>>>>>> +
>>>>>>> +Sources of IIO channels can be represented by any node in the
>>>>>>> device
>>>>>>> +tree.  Those nodes are designated as IIO providers.  IIO
>>>>>>> consumer
>>>>>>> +nodes use a phandle and IIO specifier pair to connect IIO
>>>>>>> provider
>>>>>>> +outputs to IIO inputs.  Similar to the gpio specifiers, an IIO
>>>>>>> +specifier is an array of one or more cells identifying the IIO
>>>>>>> +output on a device.  The length of an IIO specifier is defined
>>>>>>> by
>>>>>>> the
>>>>>>> +value of a #io-channel-cells property in the clock provider
>>>>>>> node.
>>>>>>> +
>>>>>>> +[1] http://marc.info/?l=linux-iio&m=135902119507483&w=2
>>>>>>> +
>>>>>>> +==IIO providers==
>>>>>>> +
>>>>>>> +Required properties:
>>>>>>> +#io-channel-cells: Number of cells in an IIO specifier;
>>>>>>> Typically 0
>>>>>>> for nodes +		   with a single IIO output and 1 for nodes 
> with
>>>>>>> multiple +		   IIO outputs.
>>>>>>> +
>>>>>>> +For example:
>>>>>>> +
>>>>>>> +    adc: adc@35 {
>>>>>>> +	compatible = "maxim,max1139";
>>>>>>> +	reg = <0x35>;
>>>>>>> +        #io-channel-cells = <1>;
>>>>>>> +    };
>>>>>>> +
>>>>>>> +==IIO consumers==
>>>>>>> +
>>>>>>> +Required properties:
>>>>>>> +io-channels:	List of phandle and IIO specifier pairs, one 
> pair
>>>>>>> +		for each IIO input to the device.  Note: if the
>>>>>>> +		IIO provider specifies '0' for #clock-cells, then
>>>>>>> +		only the phandle portion of the pair will appear.
>>>>>>> +
>>>>>>> +Optional properties:
>>>>>>> +io-channel-names:
>>>>>>> +		List of IIO input name strings sorted in the same
>>>>>>> +		order as the io-channels property.  Consumers drivers
>>>>>>> +		will use io-channel-names to match IIO input names
>>>>>>> +		with IIO specifiers.
>>>>>>> +io-channel-ranges:
>>>>>>> +		Empty property indicating that child nodes can inherit
>>>
>>> named
>>>
>>>>>>> +		IIO channels from this node. Useful for bus nodes to
>>>
>>> provide
>>>
>>>>>>> +		and IIO channel to their children.
>>>>>>> +
>>>>>>> +For example:
>>>>>>> +
>>>>>>> +    device {
>>>>>>> +        io-channels = <&adc 1>, <&ref 0>;
>>>>>>> +        io-channel-names = "vcc", "vdd";
>>>>>>> +    };
>>>>>>> +
>>>>>>> +This represents a device with two IIO inputs, named "vcc" and
>>>>>>> "vdd".
>>>>>>> +The vcc channel is connected to output 1 of the &adc device,
>>>>>>> and
>>>>>>> the
>>>>>>> +vdd channel is connected to output 0 of the &ref device.
>>>>>>> +
>>>>>>> +==Example==
>>>>>>> +
>>>>>>> +	adc: max1139@35 {
>>>>>>> +		compatible = "maxim,max1139";
>>>>>>> +		reg = <0x35>;
>>>>>>> +		#io-channel-cells = <1>;
>>>>>>> +	};
>>>>>>> +
>>>>>>> +	...
>>>>>>> +
>>>>>>> +	iio_hwmon {
>>>>>>> +		compatible = "iio-hwmon";
>>>>>>> +		io-channels = <&adc 0>, <&adc 1>, <&adc 2>,
>>>>>>> +			<&adc 3>, <&adc 4>, <&adc 5>,
>>>>>>> +			<&adc 6>, <&adc 7>, <&adc 8>,
>>>>>>> +			<&adc 9>, <&adc 10>, <&adc 11>;
>>>>>>> +		io-channel-names = "vcc", "vdd", "vref", "1.2V";
>>>>>>> +	};
>>>>>>> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
>>>>>>> index b289915..d48f2a8 100644
>>>>>>> --- a/drivers/iio/inkern.c
>>>>>>> +++ b/drivers/iio/inkern.c
>>>>>>> @@ -10,6 +10,7 @@
>>>>>>>
>>>>>>>  #include <linux/export.h>
>>>>>>>  #include <linux/slab.h>
>>>>>>>  #include <linux/mutex.h>
>>>>>>>
>>>>>>> +#include <linux/of.h>
>>>>>>>
>>>>>>>  #include <linux/iio/iio.h>
>>>>>>>  #include "iio_core.h"
>>>>>>>
>>>>>>> @@ -92,6 +93,179 @@ static const struct iio_chan_spec
>>>>>>>
>>>>>>>  	return chan;
>>>>>>>  
>>>>>>>  }
>>>>>>>
>>>>>>> +#ifdef CONFIG_OF
>>>>>>> +
>>>>>>> +static int iio_dev_node_match(struct device *dev, void *data)
>>>>>>> +{
>>>>>>> +	return !strcmp(dev->type->name, "iio_device") && dev->of_node
>>>
>>> ==
>>>
>>>>>> data;
>>>>>>
>>>>>> Hmm, do you need to check type name here? One device node should
>>>>>> rather
>>>>>> represent only one device, making node an unique identifier.
>>>>>>
>>>>>> It this is meant to be a sanity check, it could be done one time
>>>>>> after
>>>>>> finding the device.
>>>>>
>>>>> Hi Tomasz,
>>>>>
>>>>> This is what Lars had suggested earlier:
>>>>>> Yes, use bus_find_device on iio_bus_type. A nice example how to
>>>>>> use
>>>>>> this to lookup device by of node is of_find_i2c_device_by_node.
>>>>>> For
>>>>>> IIO you also need to make sure that dev->type is iio_dev_type,
>>>>>> since
>>>>>> both devices and triggers are registered on the same bus.
>>>>>
>>>>> Is it really needed, or in other words would it be sufficient to
>>>>> check
>>>>> if of_node and data match each other ? Your reasoning makes sense
>>>>> to
>>>>> me, and I had thought about it as well, but I don't really know,
>>>>> and
>>>>> I don't know how I could test it and guarantee correctness either.
>>>>> I'll be happy to take the strcmp() out if someone tells me that it
>>>>> is
>>>>> definitely not needed ...
>>>>
>>>> A IIO trigger and a IIO device may have the same of_node, e.g. if
>>>> they
>>>> both belong to the same physical device. But you don't need to do
>>>> the
>>>> strcmp just compare dev->type to iio_dev_type i.e. dev->type ==
>>>> &iio_dev_type. Although it doesn't really matter in practice first
>>>> check for the of_node then check for the type, since the of_node
>>>> will
>>>> only match for a few devices at most, the type will match for quite
>>>> a
>>>> few.
>>>
>>> I must disagree.
>>>
>>> If you have two IIO devices provided by one physical device, then in
>>>
>>> device tree they should be represented as follows:
>>> 	phys-dev@12345678 {
>>> 	
>>> 		compatible = "some-physical-device";
>>> 		/* ... */
>>> 		
>>> 		my_trig: iio-trigger {
>>> 		
>>> 			/* ... */
>>> 		
>>> 		};
>>> 		
>>> 		my_dev: iio-device {
>>> 		
>>> 			/* ... */
>>> 		
>>> 		};
>>> 	
>>> 	};
>>>
>>> Notice that phys-dev works here as an IIO bus on which its IIO devices
>>> are available. This is related to the convention that single OF
>>> device node represents single device, which would be violated
>>> otherwise.
>>
>> Right now the iio device is a child of the physical device, and I am
>> simply passing of_node on to it. guess you are saying that is not
>> correct ?
>>
>> If so, what would be the correct approach ? Something like the following
>> ?
>>
>> 	voltage-sensor@35 {
>> 		compatible = "maxim,max1139";
>> 		reg = <0x35>;
>> 		vcc-supply = <&reg_3p3v>;
>> 		vref-supply = <&reg_3p3v>;
>>
>> 		max1139-iio: iio-device {
>> 			device_type = "iio_device";
>> 			#io-channel-cells = <1>;
>> 		};
>> 	};
>>
>> and in the driver probe function:
>>
>> 	if (parent->of_node)
>> 		iio_dev->dev.of_node = of_find_node_by_type(parent->of_node,
>> "iio_device");
>>
>> Another option would be to use of_find_compatible_node() and something
>> like compatible = "iio-device";
>> in the iio-device node.
> 
> A device node is defined as a node having compatible property. Other nodes 
> should be seen as helper nodes, which do not represent devices (although 
> they all have struct device_node in Linux).
> 
> Also, AFAIK, device_type is a deprecated property used by some legacy 
> PowerPC machines and for current machines only compatible should be used.
> 
> So I guess the approach with compatible would be appropriate here.
> 
> However for physical devices providing only a single IIO device it might 
> be better to allow simpler specification, like:
> 
>  	max1139-iio: voltage-sensor@35 {
>  		compatible = "maxim,max1139", "iio_device";

I don't think this makes a lot of sense. First of all iio_device an artificial
Linux term, while the device tree should describe the hardware. Secondly there
is no generic iio driver which could match on a node with a "iio_device"
compability string and stuff would just work. I mean we don't do

compatible = "atmel,at91sam9260-i2c", "i2c-master";

or similar either.


>  		reg = <0x35>;
>  		vcc-supply = <&reg_3p3v>;
>  		vref-supply = <&reg_3p3v>;
> 		device_type = "iio_device";
>  		#io-channel-cells = <1>;
>  	};
>