linux-kernel - Re: Regulator regression in next-20180305

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Date:   Wed, 07 Mar 2018 15:37:04 +0100
From:   Maciej Purski <m.purski@...sung.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Fabio Estevam <festevam@...il.com>,
        Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: Regulator regression in next-20180305

On 03/07/2018 03:10 PM, Mark Brown wrote:
> On Wed, Mar 07, 2018 at 01:57:12PM +0100, Maciej Purski wrote:
> 
>> I'm trying to figure out what is so special about these boards. The only
>> strange thing, that I haven't noticed at first, is that all regulators share
>> a common supply - dummy regulator. It is defined in anatop_regulator.c.
> 
> No, that's a regulator framework thing - the regulator framework will
> use the dummy regulator as a supply when there's nothing described in
> the DT so long as the client doesn't explicitly tell it that the supply
> might be optional.
> 

Ok, thanks for explanation. I think I have found a possibly dangerous scenario, 
but I can't see this situation possible in Fabio's case.

Assume, that we have a chain of supplies, consisting of at least 3. Say: A->B->C.

When we're setting voltage on A, we lock it, call balance_voltage(), lock 
suppliers and call set_voltage_rdev(). So we have regulators A, B, C locked. 
Then set_voltage_rdev() is trying to set voltage of its supply by calling 
set_voltage_unlocked().

Now we're on the regulator B. Set_voltage_unlocked() calls balance_voltage(), 
which again locks its supplies, if they exist. B's supply is C, so we end up 
with having a deadlock on regulator C.

Tony and Fabio, do you find this scenario possible on your boards?

Best regards
Maciej Purski