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

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

On 02/03/2013 09:58 PM, Jonathan Cameron wrote:
> On 02/03/2013 06:55 PM, Lars-Peter Clausen wrote:
>> 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.
> Lars, what you say here doesn't cover one 'interesting' case.
> 
> An iio_device has one aspect in which it is not artificial. It represents
> a group of channels that may be sampled at 'one instance' on a given device.

I primarily meant the term IIO.

- Lars