Re: [PATCH 1/3] ARM: dts: imx6: phycore-som: fix arm and soc minimum voltage

Marco Felsch
2019-12-05T07:19:49Z

Hi Stefan,

On 19-12-03 13:37, Stefan Riedmüller wrote:
> Hi Lucas, hi Marco,
>
> On 03.12.19 12:44, Lucas Stach wrote:

...

> >
> > The DT constraints are supposed to reflect absolute maximum ratings of
> > the board design. The regulator driver already knows the limits of the
> > PMIC chip, so there is no point in duplicating this information in the
> > DT.
> >
> > The DT constraints are there to make sure the regulator core can
> > constrain the voltage setting to something safe for the specific
> > design. A consumer driver bug must never be able to set a voltage that
> > is outside of the absolute maximum ratings of _all_ consumers of this
> > specific power rail. I know that a lot of DTs get this detail wrong,
> > but we shouldn't block patches to fix this. :)
>
> Thanks for the clarification and the example. I got it now and will keep it
> in mind for the future.
>
> >
> > > > If I have this wrong and the maintainers agree with you could you please
> > > > make sure to account for the bypass mode as well since these values from the
> > > > datasheet are valid too?
> > >
> > > As I said, the bypass mode isn't supported by the driver and all imx6
> > > based devicetrees follow that case. So we don't have to take that into
> > > account. Also we can't meet both contraints with one dt and futhermore
> > > the bypass mode decrease your imx6 lifetime due the the increased ripple
> > > on the arm-core supply. So I think no one wants this setup in the near
> > > future.
> >
> > As a violation of the minimum voltage setting is very unlikely to cause
> > any permanent damage to the design (expect if you got reverse voltage
> > flows somewhere) I think it is safe to include the LDO bypass supply
> > limits as the lower bound in the DT constraints, even if this mode
> > isn't currently used anywhere.
>
> Sounds good to me.

Okay, I will use the bypass value and add a comment. Stefan can you take
a look at the other patches as well?

Regards,
Marco

> Regards,
> Stefan
>
> >
> > Regards,
> > Lucas
> >
>

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