linux-kernel - Re: [PATCH] regulator: core: Keep boot

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Date:	Wed, 25 Apr 2012 17:44:30 +0200
From:	Ulf Hansson <ulf.hansson@...ricsson.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mattias WALLIN <mattias.wallin@...ricsson.com>,
	Jonas ABERG <jonas.aberg@...ricsson.com>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH] regulator: core: Keep boot_on regulators powered during
 init

On 04/25/2012 05:34 PM, Jassi Brar wrote:
>> On Mon, Apr 23, 2012 at 02:45:10PM +0200, Ulf Hansson wrote:
>>
>>> If the platform already have booted from the eMMC card, the card is
>>> already powered an initialized from a bootloader. Cutting the power
>>> without first notifying the card by sending commands to it, must be
>>> prevented and also violates the eMMC specification. In the end, it
>>> will mean that the detect and initialization procedure fails.
>>
>   Shouldn't the bootloader be responsible for ensuring MMC is
> put down after using it and before passing control to the kernel.

This is kind of complicated. eMMC is powered by two regulators. VCC and 
VCCQ. Cutting VCC uncontrolled is not allowed. If doing so anyway there 
is two options to recover.

1. Cut VCCQ as well and do full reinit of the eMMC
2. Pull a hw-reset pin to the eMMC and do a full reinit of the eMMC.

In some cases neither is possible due to HW constraints. Thus we have to 
make sure VCC is not cut.

>
>   Even if the bootloader didn't power off properly, unless there is
> some outstanding data to be written when the kernel is passed
> control, perhaps it's not that serious?

The kernel will not be to re-init the eMMC... quite serious. :-)

Kind regards
Ulf Hansson
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