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Re: [RFC 0/5] drivers: Add boot constraints core

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On 30-06-17, 12:05, Chen-Yu Tsai wrote:
> On Fri, Jun 30, 2017 at 11:55 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > On 30-06-17, 11:33, Chen-Yu Tsai wrote:
> >> AFAIK regulator constraints are supposed to satisfy all users of it.
> >
> > Right.
> >
> >> >> >Let me try with an example. A regulator is shared between LCD and DMA
> >> >> >controller.
> >> >> >
> >> >> >Operable ranges of the regulator: 1.8 - 3.0 V
> >> >> >Range required by LCD: 2.0 - 3.0 V
> >> >> >Range required by DMA: 1.8 - 2.5 V
> >>
> >> So for the example here, the regulator constraint should be 2.5 - 3.0 V,
> >> or the intersection of all voltage requirements.
> >
> > Had a look at regulator_check_consumers() and the range selected by it
> > is the *highest* min_uV and *lowest* max_uV, to find that intersection
> > point.
> >
> > For LCD: min_uV = 2.0 V, max_uV = 3.0 V
> > For DMA: min_uV = 1.8 V, max_uV = 2.5 V
> >
> > Highest min_uV = 2.0 V
> > Lowest max_uV = 2.5 V
> >
> > And so I mentioned the regulator's final range (that satisfies all
> > consumers) is 2 - 2.5 V.
> >
> > Why do you say it should be 2.5 - 3.0 V ?
> 
> You are right. It should be 2.0 - 2.5 V. Haven't had my coffee this
> morning. :(

And I was worrying if I had something else in my coffee :)

> I also want to mention that for DT based platforms, this constraint
> should already be set in the device tree for the regulator, so the
> scenario where DMA comes up and sets a voltage level that LCD cannot
> use should not even be possible.

Yes, such constraints are already present. But the problem (this
series is trying to solve) is that the kernel doesn't know if the LCD
is already powered ON. And so when DMA gets probed first, the kernel
thinks that DMA is the only user of the regulator and the voltage is
set to 1.8-2.5 V. And so this series is somehow trying to make the
kernel aware about the constraints of the LCD controller which was
enabled in the bootloader.

-- 
viresh

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[RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-28 12:30 +0200
  [RFC 1/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-28 12:30 +0200
    Re: [RFC 1/5] drivers: Add boot constraints core Randy Dunlap <rdunlap@infradead.org> - 2017-06-28 18:00 +0200
      Re: [RFC 1/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-29 06:00 +0200
        Re: [RFC 1/5] drivers: Add boot constraints core Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-06-29 15:00 +0200
          Re: [RFC 1/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-29 17:00 +0200
  Re: [RFC 0/5] drivers: Add boot constraints core "Enrico Weigelt, metux IT consult" <enrico.weigelt@gr13.net> - 2017-06-29 14:50 +0200
    Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-29 16:50 +0200
      Re: [RFC 0/5] drivers: Add boot constraints core "Enrico Weigelt, metux IT consult" <enrico.weigelt@gr13.net> - 2017-06-29 17:10 +0200
        Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-30 05:20 +0200
          Re: [RFC 0/5] drivers: Add boot constraints core Chen-Yu Tsai <wens@csie.org> - 2017-06-30 05:40 +0200
            Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-30 06:00 +0200
              Re: [RFC 0/5] drivers: Add boot constraints core Chen-Yu Tsai <wens@csie.org> - 2017-06-30 06:10 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-30 06:20 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Chen-Yu Tsai <wens@csie.org> - 2017-06-30 06:30 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-30 07:20 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Chen-Yu Tsai <wens@csie.org> - 2017-06-30 08:40 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-30 10:50 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Mark Brown <broonie@kernel.org> - 2017-06-30 14:20 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-03 08:20 +0200
                Re: [RFC 0/5] drivers: Add boot constraints core Mark Brown <broonie@kernel.org> - 2017-06-30 14:20 +0200
  Re: [RFC 0/5] drivers: Add boot constraints core Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-06-29 14:50 +0200
    Re: [RFC 0/5] drivers: Add boot constraints core "Enrico Weigelt, metux IT consult" <enrico.weigelt@gr13.net> - 2017-06-29 15:10 +0200
    Re: [RFC 0/5] drivers: Add boot constraints core Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-29 17:00 +0200
      Re: [RFC 0/5] drivers: Add boot constraints core Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-06-29 17:50 +0200
        Re: [RFC 0/5] drivers: Add boot constraints core Stephen Boyd <sboyd@codeaurora.org> - 2017-06-29 23:10 +0200

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