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

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

On 02/03/2013 05:31 PM, Guenter Roeck wrote:
> On Sun, Feb 03, 2013 at 12:29:23PM +0100, 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.
>>
> iio_dev_type is defined as static variable in industrialio-core.c, which can be
> loaded as module. To use it in inkern.c, I would have to move it there and make
> it global. I can do that, but is it worth it just to safe the strcmp ?

inkern.c and industrialio-core.c are in the same compilation unit as far as I
can see:

industrialio-y := industrialio-core.o industrialio-event.o inkern.o

So I don't see a problem there, just make it non-static and a declaration for
it to iio-core.h. Or maybe even better add a of_find_iio_device_by_node() function.

- Lars