linux-kernel - Re: [PATCH] mmc: core: Check regulator pointer

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Date:   Tue, 18 Oct 2016 12:28:36 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     linux-mmc <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: core: Check regulator pointer

On 18 October 2016 at 11:47, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> 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@...e-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?

Through some other way, which is managed by the internal logic of the
mmc controller.

>
> 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.

Yes, you are right. For most cases, but not all.

Kind regards
Uffe