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

On 05/05/11 11:16, Alexander Stein wrote:

Am Donnerstag, 5. Mai 2011, 12:01:25 schrieb Jonathan Cameron:

quoted

On 05/05/11 10:44, Alexander Stein wrote:

quoted

Am Donnerstag, 5. Mai 2011, 11:08:18 schrieb Jonathan Cameron:

quoted

On 05/05/11 09:32, Alexander Stein wrote:

quoted

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).