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

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Date:	Wed, 25 Apr 2012 22:01:49 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Ulf Hansson <ulf.hansson@...ricsson.com>
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 25 April 2012 21:14, Ulf Hansson <ulf.hansson@...ricsson.com> wrote:
> On 04/25/2012 05:34 PM, Jassi Brar wrote:
>>>
>>  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.
>
I meant power-down to whatever extent your h/w permits. The rest you'll
have to take care by appropriately flagging supplies in the kernel.

If not full power-off, couldn't your bootloader atleast send eMMC the necessary
"power-down sequence of commands", so that it responds well to next
power-up sequence of commands ?

The point being, the board files, in both your bootloader and kernel, ought to
know the h/w constraints and program the regulator api accordingly.

Generalizing the case, IMHO it's not feasible for every stack in the kernel to
assume it has to first cleanly shutdown the h/w before probing it.

>>  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. :-)
>
Not unless your board files flag the supplies accordingly, always_on,
and the bootloader sent eMMC the "deadly command seq" ;)
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