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

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

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.

Which one is preferred ?

Thanks,
Guenter