From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1376491467.18617.41.camel@hornet> Subject: Re: [PATCH v3 2/5] ARM: dts: add reference voltage property for MXS LRADC From: Pawel Moll To: Jonathan Cameron Cc: Hector Palacios , "linux-iio@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "devicetree-discuss@lists.ozlabs.org" , "alexandre.belloni@free-electrons.com" , "lars@metafoo.de" , "fabio.estevam@freescale.com" , "marex@denx.de" , "rob.herring@calxeda.com" , Mark Rutland , Stephen Warren , Ian Campbell Date: Wed, 14 Aug 2013 15:44:27 +0100 In-Reply-To: <520AA3CD.1040008@kernel.org> References: <1374501843-19651-1-git-send-email-hector.palacios@digi.com> <1374501843-19651-3-git-send-email-hector.palacios@digi.com> <520AA3CD.1040008@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 List-ID: 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. > >=20 > > diff --git a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lrad= c.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 > > =20 > > 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 > > +=09 maximum voltage that can be measured at full scale in each chan= nel > > +=09 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? 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. Pawel