Re: [PATCH] mmc: core: Check regulator pointer

[Shawn Lin]

å 2016/10/18 17:47, Maxime Ripard åé:
> Hi,
>
> On Tue, Oct 18, 2016 at 11:03:02AM +0200, Ulf Hansson wrote:
> > On 18 October 2016 at 10:43, Maxime Ripard
> > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:
> > > mmc_regulator_get_supply might silently fail if the regulators are not
> > > found, which is the right thing to do since both these regulators are
> > > optional.
> > >
> > > However, the drivers then have no way to know whether or not they should
> > > proceed and call mmc_regulator_set_ocr. And since this function doesn't
> >
> > Host drivers should check "if (!IS_ERR(mmc->supply.vmmc))" before
> > invoking mmc_regulator_set_ocr(). I wasn't aware that some didn't.
>
> Ok, so the sunxi one definitely doesn't:
> http://lxr.free-electrons.com/source/drivers/mmc/host/sunxi-mmc.c#L735
>
> > My point is, that in some cases the regulator is optional, then a host
> > driver need to take other actions to power on/off the card.
>
> What are those actions? Just power up the card through some other
> mean, or is it more tied to the MMC protocol?
>
> Also, I'm wondering if VMMC is actually optional at all. In all cases
> I can think of, it would be represented as a regulator anyway.

If I understand your point correctly, for sunxi's mmc controller, the
only way to power-on/off the vmmc is to call  mmc_regulator_set_ocr?

There are some cases for mmc-core/host to control the power:
1) assign a vmmc-supply for no matter of gpio-based regulator or PMIC
2) use mmc_pwrseq which is often used by sdio fucntion or emmc.
3) use a functional port to control it which is similar to gpio-based
regulator but the host drivers could control this via internal register,
for instance, dw_mmc..

4) And I even see some boards use fixed power which means we cannot
power off vmmc from the hardware part. And also, if I decide to add
alwyas-on and boot-on for the vmmc regulator I was using, and also
there is  no really need for mmc-core/driver to know whether we have
vmmc, right!?



> Thanks,
> Maxime


--
Best Regards
Shawn Lin