On Thu, 3 May 2012, Mark Brown wrote:
> On Thu, May 03, 2012 at 05:05:36PM +0200, Guennadi Liakhovetski wrote:
>
> > + ret = mmc_regulator_get_ocrmask(supply);
> > + if (ret > 0)
> > + mmc->ocr_avail = ret;
> > +
> > + if (regulator_can_change_status(supply)) {
> > + mmc->caps |= MMC_CAP_POWER_OFF_CARD;
> > + return supply;
> > + }
> > +
> > + devm_regulator_put(supply);
> > +
> > + if (ret <= 0)
> > + dev_warn(dev, "Ignoring useless (dummy?) regulator\n");
>
> This code seems very tricky and a bit confusing - you're checking that
> either you can change the voltage or change the status but you're doing
> it in a fairly abstruse way and it'll come out as saying that a fixed
> voltage regulator is a useful regulator to have which probably isn't what
> you want if it's worth ignoring a dummy regulator.
This function handles 3 cases:
1. A regulator that can (in principle) change state, i.e., switch on and
off. Such a regulator is good to keep for the runtime to power up and down
the card.
2. A regulator, that cannot switch, but at least can tell its supplied
voltage is used ones to read out supported voltages and released again.
3. A regulator that can do none of the above is defined as "useless"
So, a fixed voltage regulator is indeed a useful one - it can tell us the
voltage and maybe even switch power. A dummy regulator can do none of the
above.
> You may also run into trouble on boards that use the ability to disable
> unused regulators at the end of boot - they'll power things off even
> without the ability to change status at runtime.
Aha, you mean, I shouldn't put() the regulator, even if it cannot change
status itself? Can this also happen with a dummy regulator?
> It'd at least be nice to write things more directly, or add some
> comments.
Hm, sure, I can add some comments:-)
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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