Messages in this thread | | | Subject | Re: [PATCH] mmc: core: Check regulator pointer | From | Shawn Lin <> | Date | Tue, 18 Oct 2016 20:29:07 +0800 |
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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.ripard@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
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