Re: [PATCH] ads7846: Add possibility to use external vref on ads7846

[Alexander Stein <alexander.stein@systec-electronic.com>]

Am Donnerstag, 5. Mai 2011, 12:33:53 schrieb Jonathan Cameron:
> On 05/05/11 11:16, Alexander Stein wrote:
> > Am Donnerstag, 5. Mai 2011, 12:01:25 schrieb Jonathan Cameron:
> >> On 05/05/11 10:44, Alexander Stein wrote:
> >>> Am Donnerstag, 5. Mai 2011, 11:08:18 schrieb Jonathan Cameron:
> >>>> On 05/05/11 09:32, Alexander Stein wrote:
> >>>>> Just set vref_mv in your platform config to use external vref.
> >>>>> Otherwise the internal one is used.
> >>>> 
> >>>> Would be nicer to see this done with the regulator framework. But then
> >>>> if you have a use case on a board where that isn't available, then
> >>>> fair enough.
> >>> 
> >>> Well, for the regulator framework I would redesign the driver a bit.
> >>> Currently the analogue inputs are displayed as mV in sysfs. If the
> >>> current analogue input voltage is shown via the regulator framework the
> >>> ads7846 driver itself can shows the actual ADC values. The latter ones
> >>> don't need to know the reference voltage.
> >>> But I think this is a different problem than choosing the reference
> >>> voltage for an ADC for what this patch is for.
> >> 
> >> I'm somewhat confused by what you mean here.  The regulator framework is
> >> all about power supplies.  This device would merely be a consumer that
> >> asks for what (if anything) is being uspplied to the external vref line.
> >> Basically it's a more general alternative to supplying the value via
> >> platform data.
> > 
> > Maybe I did get you wrong. I thought you meant retrieving the voltage at
> > the analogue input somehow using the regulator framework.
> > I don't know much about this framework, so how can you handle this: The
> > external vref is board-specific, e.g. hard-wired to 3,3V? There is no
> > regulator which could adjust the voltage attached to ext vref.
> 
> Yup, you specify it as a fixed voltage regulator.  The reason to do this
> is that others may well wire it up to a variable regulator (typical
> embedded pmic chip for example).

Ok, sounds ok to me. But you will then require the regulator framework to be 
setup for each board using the ads7846 driver.
Nevertheless I don't have an elegant idea to switch between internal vref 
(which is 2,5V fixed) and the (possible variable) ext vref in board-setup.

Alexander