On 02/03/2013 12:39 PM, Jonathan Cameron wrote: > On 02/02/2013 04:10 PM, Guenter Roeck wrote: >> On Sat, Feb 02, 2013 at 10:29:02AM +0000, Jonathan Cameron wrote: >>> On 01/31/2013 09:43 PM, Guenter Roeck wrote: >>>> Provide bindings, new API access functions, and parse OF data >>>> during initialization. >>>> >>> Firstly thanks for working on this Guenter, it's been a big hole >>> for a while largely because non of our largest developers were >>> actually using development platforms with device tree support. >>> >>> Given my knowledge of device tree is based on the odd article >>> and looking at similar sets of bindings this morning, my comments >>> are likely to be somewhat superficial and uninformed ;) >>> >>> Mostly on this one I'll take a back seat and let those who >>> know this stuff better come to a consensus. >>> >>> Jonathan >>> >>>> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> >>>> --- >>>> .../devicetree/bindings/iio/iio-bindings.txt | 97 ++++++++ >>>> drivers/iio/inkern.c | 241 ++++++++++++++++---- >>>> include/linux/iio/consumer.h | 8 + >>>> 3 files changed, 299 insertions(+), 47 deletions(-) >>>> 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..0f51c95 >>>> --- /dev/null >>>> +++ b/Documentation/devicetree/bindings/iio/iio-bindings.txt >>>> @@ -0,0 +1,97 @@ >>>> +This binding is a work-in-progress, and are based on clock bindings and >>>> +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 more 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. >>>> + >>>> +Optional properties: >>>> +io-channel-output-names: >>>> + Recommended to be a list of strings of IIO output signal >>>> + names indexed by the first cell in the IIO specifier. >>>> + However, the meaning of io-channel-output-names is domain >>>> + specific to the IIO provider, and is only provided to >>>> + encourage using the same meaning for the majority of IIO >>>> + providers. This format may not work for IIO providers >>>> + using a complex IIO specifier format. In those cases it >>>> + is recommended to omit this property and create a binding >>>> + specific names property. >>>> + >>>> + IIO consumer nodes must never directly reference >>>> + the provider's io-channel-output-names property. >>>> + >>>> +For example: >>>> + >>>> + adc: adc@35 { >>>> + compatible = "maxim,max1139"; >>>> + reg = <0x35>; >>>> + #io-channel-cells = <1>; >>>> + io-channel-output-names = "adc1", "adc2"; >>>> + }; >>>> + >>>> +- this node defines a device with two named IIO outputs, the first named >>>> + "adc1" and the second named "adc2". Consumer nodes always reference >>>> + IIO channels by index. The names should reflect the IIO output signal >>>> + names for the device. >>>> + >>>> +==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"; >>> Having different numbers of channels and channel names seems >>> unusual... Deliberate or you got bored making up channel names? >>> >>> Why use indexed values for <&adc 0> etc rather than the output >>> channel names on adc? For the iio_map stuff we initialy used >>> indexes but got a lot of responses that it was a silly idea and >>> naming was much more consistent and easy to follow. >>> >>> Is there a fundamental reason for it here? >>> >>> (note I don't mind either way as this seems more compact and cleaner >>> in some ways) >>> >> >> It follows the structure used by clocks, which uses the provided name(s) to >> calculate an index into io-channels. This way, the provider does not have to >> provide the mapping, the consumer does not have to know the io-channel index, >> and the consumer code can call something like >> >> channel = iio_get_channel(dev, "vcc"); >> >> In the above example, "vcc" will map to "<&adc, 0>", and "vref" to "<&adc, 2>". >> >> This works for both platform data and OF data (though platform data will >> still need provider-based mapping, at least for now). >> >> This lets the code use a static name (eg "vcc"), and the mapping to the actual >> provider happens through devicetree. Since the name is only used locally and >> consumer driver specific, there is no need to define globally unique names. >> >> With this approach, the io channel map is not needed at all for the OF case. >> I had used it in this version of the patch set, but got rid of it now. >> >> Actually, provider based mapping doesn't even work. If the consumer is >> instantiated before the provider, the mapping doesn't exist yet, and the >> call to iio_channel_get_all will fail. There is no way to prevent this, >> as providers can come online at any time and there is no means to enforce that >> all providers are already active by the time the consumers are instantiated. >> Even if a mapping exists, there is no way to know if it is complete, if a >> consumer is mapped to multiple providers. >> >> With the consumer based mapping, iio_channel_get_all 'knows' that not all >> requested providers are available and can return -EPROBEDEFER in that case. > Thanks. That makes sense. At the moment iio_hwmon is the only case that > does a 'get all'. Clearly things are easier when the driver is requesting a > specific set and we can do the back off much more easily. > >> >> As a side effect, we can also use the names - if provided - as channel >> labels in iio_hwmon. >> >> Note this will require the iio_get_channel API to change from taking the >> consumer device name to taking the consumer device pointer as argument. >> This will enable it to work for both OF and non-OF cases, should address Lars' >> concerns about duplicate API functions, and synchronize the code to match how >> the clock framework works. > > Agreed, doing this gives us a cleaner syntax as well. Note there are other > users of that function in tree so be sure to get them all! > >> >> Thanks, >> Guenter > Thanks for the explanation. What I was actually suggesting was something > like: > > adc: max1139@35 { > compatible = "maxim,max1139"; > reg = <0x35>; > #io-channel-cells = <1>; > io-channel-output-names = "adc1", "adc2", "adc3" > }; > > iio_hwmon { > compatible = "iio-hwmon"; > io-channels = <&adc "adc1">, <&adc "adc2">, <&adc "adc3">, > io-channel-names = "vcc", "vdd", "vref"; > } > > Having taken a look at the available syntax, those <> pairs have > to be unsigned integers? Hence the additional level of indirection? Yea, I think mixing phandles and strings simply doesn't work, due how devicetree stores things. > > (sorry, I'm getting you to give me a tutorial on device tree syntax rather > than the actual issue here!) > > I guess it was desirable to keep the syntax relatively simple but that occasionally > adds the requirement for a bit of indirection. > > > > Jonathan -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
