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

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On 02/03/2013 12:52 PM, 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@xxxxxxxxxxxx>
>>>>> ---
>>>>> - 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.

But we do some_dev->of_node = some_other_dev->of_node, all over the place. How
is that different?

- Lars
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