From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pawel Moll Subject: Re: [PATCH v3 2/5] ARM: dts: add reference voltage property for MXS LRADC Date: Wed, 14 Aug 2013 15:44:27 +0100 Message-ID: <1376491467.18617.41.camel@hornet> 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 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <520AA3CD.1040008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: linux-iio-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jonathan Cameron Cc: Hector Palacios , "linux-iio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org" , "alexandre.belloni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org" , "lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org" , "fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org" , "marex-ynQEQJNshbs@public.gmane.org" , "rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org" , Mark Rutland , Stephen Warren , Ian Campbell List-Id: devicetree@vger.kernel.org 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? 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