在 2016/10/18 17:47, Maxime Ripard 写道:
Hi,

On Tue, Oct 18, 2016 at 11:03:02AM +0200, Ulf Hansson wrote:
On 18 October 2016 at 10:43, Maxime Ripard
<maxime.rip...@free-electrons.com> 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

Reply via email to