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? (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 > -- 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
