Sorry accidental HTML message hence resend Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx> wrote: >Hi Pawel, > >On 14/08/2013 16:44, Pawel Moll wrote: >> On Tue, 2013-08-13 at 22:23 +0100, Jonathan Cameron wrote: >>> On 07/22/13 15:04, Hector Palacios wrote: >>>> Some LRADC channels have fixed pre-dividers so they can measure >>>> different voltages at full scale. The reference voltage allows to >>>> expose a scaling attribute through the IIO sysfs so that a user can >>>> compute the real voltage out of a measured sample value. >>>> >>>> diff --git >a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt >b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt >>>> index 4688205..6ec485c 100644 >>>> --- >a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt >>>> +++ >b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt >>>> @@ -1,9 +1,12 @@ >>>> * Freescale i.MX28 LRADC device driver >>>> >>>> Required properties: >>>> -- compatible: Should be "fsl,imx28-lradc" >>>> +- compatible: "fsl,imx28-lradc", "fsl,imx23-lradc" >>>> - reg: Address and length of the register set for the device >>>> - interrupts: Should contain the LRADC interrupts >>>> +- fsl,vref: Reference voltage (in mV) for each LRADC channel. This >is the >>>> + maximum voltage that can be measured at full scale in each >channel >>>> + considering fixed pre-dividers. >> >> So, let me try to rephrase what I read above. >> >> There's an ADC with X channels. And there's a reference voltage >source >> (one?). Now, each of the ADC channels have a (different?) voltage >> divider, taking the voltage from the reference source and feeding it >to >> the ADC comparator. How much am I wrong? >> > >You are not so wrong. There is indeed actually only one reference >voltage (and that is 1.85V). But, before feeding the voltage to the ADC >channels, you sometimes have a divider. Then, after the channel muxing, >you can add a by 2 divider. > >Mandatory ascii art: > > +-----+ > | | > +-ch1--->| | > | | > | | > | | +-----+ > +-ch2--->| | | | > | MUX |++-->| ADC +-----------> > ch3 | | | | | > +----+ | | | +-----+ > | | | | | | > +-> :4 +->| | | +---+--+ > | | | | | | | > +----+ | | +->| :2 | > +-----+ | | > +------+ > > >> If I'm not wrong at all, I'd say that the reference source could be >> described as a standard fixed regulator >> (Documentation/devicetree/bindings/regulator/fixed-regulator.txt) and >> the ADC node should have some king of "reference-supply" phandle to >the >> regulator node. Now, if the dividers factors are *really* fixed, the >> driver could know about them and calculate the effective reference >> voltage on its own, couldn't it? >> >> Let me repeat the "DT standard disclaimer": the tree, in general, >should >> describe the way components are *wired up*, not much more. >> > >So, from my point of view, the divider that is before the mux (the by 4 >divider on channel 3 on my drawing) is not part of the the ADC, it is >not fixed by that IP. And indeed, that changed between the i.mx23 and >i.mx28 while the IP is the same. > >So, the two solutions you suggest are: >1/ using a fixed-regulator phandle per channel >2/ hard-coding the dividers in the driver using the compatible string >to >know which divider is on which channel. > >I feel that solution 2 is less future proof but at the same time, I >don't believe we will see that IP in another chip in the future. > >Are my explanations clear enough to take a decision ? > >-- >Alexandre Belloni, Free Electrons >Embedded Linux, Kernel and Android engineering >http://free-electrons.com >-- >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 I would favour option 2 though some of the discussions going on at the moment about bindings might result in a generic description of this and any other bits of analog front end. -- Sent from my Android phone with K-9 Mail. Please excuse my brevity. -- Sent from my Android phone with K-9 Mail. Please excuse my brevity. -- 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
