From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shawn Lin Subject: Re: [PATCH] mmc: core: Check regulator pointer Date: Tue, 18 Oct 2016 20:29:07 +0800 Message-ID: References: <20161018084343.680-1-maxime.ripard@free-electrons.com> <20161018094704.ohubpg4j3jhc7cay@lukather> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: Received: from lucky1.263xmail.com ([211.157.147.135]:38800 "EHLO lucky1.263xmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754431AbcJRM3U (ORCPT ); Tue, 18 Oct 2016 08:29:20 -0400 In-Reply-To: <20161018094704.ohubpg4j3jhc7cay@lukather> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Maxime Ripard , Ulf Hansson Cc: shawn.lin@rock-chips.com, linux-mmc , "linux-kernel@vger.kernel.org" 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 >> 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