On Thu, 2014-11-06 at 08:55 -0800, Bjorn Andersson wrote:
> On Wed, Nov 5, 2014 at 11:54 PM, Ivan T. Ivanov <iivanov@mm-sol.com> wrote:
> > On Wed, 2014-11-05 at 17:36 -0800, Bjorn Andersson wrote:
> > > On Wed, Nov 5, 2014 at 10:31 AM, Ivan T. Ivanov <iivanov@mm-sol.com> wrote:
> [..]
> > > > Some of the child device drivers have to know PMIC chip revision.
> > > > 
> > > 
> > > So your plan is to have a strstr(parent->compatible, "-v2") there?
> > 
> > Actually also PMIC subtype (pm8841, pm8226...) is also required, so
> > the plan is to have something like this:
> > 
> > {
> >         static const struct of_device_id pmic_match_table[] = {
> >                 { .compatible = "qcom,pm8941-v1.0" },
> >                 { .compatible = "qcom,pm8841-v0.0" },
> >                 { }
> > 
> >         };
> > 
> >         const struct of_device_id *match;
> > 
> >         match = of_match_device(pmic_match_table, pdev->dev.parent);
> >         if (match) {
> >                 dev_info(&pdev->dev, "%s chip detected\n", match->compatible);
> >         }
> > }
> > 
> 
> To me this is a hack, you should not alter the devicetree to make it
> "better express the hardware". Either you know these things from boot
> and they go in device tree, or you can probe them and they should not
> go in device tree.
> 
> If you really need these values you should expose them through some api.

I would like to avoid compile time dependency between these drivers.
There are several precedents of using of_update_property() for enhancing
compatible property already.  

> 
> > > Could you be a little bit more elaborate on what you're trying to do
> > > and which child devices that might be?
> > 
> > For example ADC drivers are required temperature compensation based
> > on PMIC variant and chip manufacturer.
> > 
> 
> I see, is that compensation of any practical value? Or is the
> compensation of academic proportions?

It depends of what you mean by academic :-). Attached file have test
application which dump difference between non compensated and compensated
values for different temperature, manufacture and input value.

Output format of the program is:
Column 1: manufacturer GF=0, SMIC=1, TSMC=2
Column 2: chip revision
Column 3: die temperature in mili deg Celsius 
Column 4: input for compensation in micro Volts
Column 5: compensated result in micro Volts
Column 6: difference in micro Volts


Regards,
Ivan