linux-kernel - Re: [PATCH 0/2] IO voltage domain support for rk3188 and rk3288

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Date:	Thu, 4 Sep 2014 18:51:47 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Kevin Hilman <khilman@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Doug Anderson <dianders@...omium.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Mark Brown <broonie@...nel.org>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Addy Ke <addy.ke@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Andy Gross <agross@...eaurora.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sandeep Nair <sandeep_n@...com>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Thierry Reding <treding@...dia.com>, Nishanth Menon <nm@...com>
Subject: Re: [PATCH 0/2] IO voltage domain support for rk3188 and rk3288

On Sat, Aug 30, 2014 at 1:27 PM, Heiko Stübner <heiko@...ech.de> wrote:
> Am Freitag, 29. August 2014, 21:51:46 schrieb Doug Anderson:
>> On Thu, Aug 28, 2014 at 2:26 PM, Santosh Shilimkar
>>
>> <santosh.shilimkar@...com> wrote:
>> > On Thursday 28 August 2014 03:36 PM, Doug Anderson wrote:
>> >> These two patches add support for automatically configuring the IO
>> >> voltage domains on rk3188 and rk3288 SoCs.  The first patch adds some
>> >> new notification types to the regulator code.  It's used by the second
>> >> patch which actually implements the IO voltage domain driver.
>> >>
>> >> These two patches were co-developed by Heiko Stübner and Doug Anderson
>> >> (proof of concept patches were written by Heiko).  They were tested in
>> >> a private branch on an rk3288 board using rk808 instead of mainline
>> >> since rk808 support isn't finalized in mainline yet.
>> >>
>> >> (sorry if you got this series twice; my mailer seems unhappy with me)
>> >>
>> >> Heiko Stübner (2):
>> >>   regulator: core: Add REGULATOR_EVENT_PRE_VOLTAGE_CHANGE (and ABORT)
>> >>   soc/rockchip: io-domain: add driver handling io domains
>> >
>> > Sorry to shot down but your IO domains are nothing but voltage domains
>> > and you should really build something in the drivers/power/*
>>
>> If everyone agrees that this belongs in drivers/power that's totally
>> OK.  Neither Heiko nor I was confident that it should be in
>> drivers/soc.  I had even though that the code wouldn't be totally out
>> of place in the Rockchip pinctrl driver (adding Linus W since I think
>> some SoCs did add code to handle 3.3V vs. 1.8V in pinctrl).
>
> a bit of context for Linus ...
>
> This is essentially the continuation of  the thread "io-domain voltages as
> regulators?" from the beginning of august. After more discussions we found out
> that the io voltage selection I asked about is not an independent supply, but
> instead has to reflect the voltage of the real supplying regulator.
>
> And setting the io-voltage setting to 1.8V while the regulator is supplying
> 3.3V for example may actually damage the chip.
>
>
> So in our current approach here, we added a driver that tracks voltage changes
> of the supplying regulator via a notifier and sets the register bits
> accordingly.

I feel I'm not smart enough for this. You need the PM people to look
at this stuff, like Rafael Wysocki, Kevin Hilman and Ulf Hansson.

Since it is also MMC/SD UHS-related, Ulf should know better than
most what is needed, plus he's working on generic power domains
right now.

Yours,
Linus Walleij
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