linux-kernel - Re: [PATCH v3 3/6] dt-bindings: mfd: da9062: add regulator voltage selection documentation

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Date:   Tue, 7 Jan 2020 09:36:54 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Support Opensource <Support.Opensource@...semi.com>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        "andrew@...id.au" <andrew@...id.au>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 3/6] dt-bindings: mfd: da9062: add regulator voltage
 selection documentation

Hi Mark,

On 19-12-17 12:58, Mark Brown wrote:
> On Tue, Dec 17, 2019 at 08:35:33AM +0100, Marco Felsch wrote:
> > On 19-12-16 11:44, Mark Brown wrote:
> 
> > > What I'm saying is that I think the binding needs to explicitly talk
> > > about that since at the minute it's really confusing reading it as it
> > > is, it sounds very much like it's trying to override that in a chip
> > > specific fashion as using gpiolib and the GPIO bindings for pinmuxing is
> > > really quite unusual.
> 
> > Hm.. I still think that we don't mux the pin to some special function.
> > It is still a gpio input pin and if we don't request the pin we could
> > read the input from user-space too and get a 'valid' value. Muxing would
> > happen if we change the pad to so called _alternate_ function. Anyway,
> > lets find a binding description:
> 
> I don't think any of this makes much difference from a user point of
> view.
> 
> > IMHO this is very descriptive and needs no update.
> 
> > description:
> >  - A GPIO reference to a local general purpose input, [1] calls it GPI.
> >    The DA9062 regulators can select between voltage-a/-b settings.
> >    Each regulator has a VBUCK*_GPI or VLDO*_GPI input to determine the
> >    active setting. In front of the VBUCK*_GPI/VLDO*_GPI input is a mux
> >    to select between different signal sources, valid sources are: the
> >    internal sequencer, GPI1, GPI2 and GPI3. See [1] table 63 for more
> >    information. Most the time the internal sequencer is fine but
> >    sometimes it is necessary to use the signal from the DA9062 GPI
> >    pads. This binding covers the second use case.
> >    Attention: Sharing the same GPI for other purposes or across multiple
> >    regulators is possible but the polarity setting must equal.
> 
> This doesn't say anything about how the GPIO input is expected to be
> controlled, for voltage setting any runtime control would need to be
> done by the driver and it sounds like that's all that can be controlled.
> The way this reads I'd expect one use of this to be for fast voltage
> setting for example (you could even combine that with suspend sequencing
> using the internal sequencer if you mux back to the sequencer during
> suspend).

The input signal is routed trough the da9062 gpio block to the
regualtors. You can't set any voltage value using a gpio instead you
decide which voltage setting is applied. The voltage values for
runtime/suspend comes from the dt-data. No it's not just a fast
switching option imagine the system suspend case where the cpu and soc
voltage can be reduced to a very low value. Older soc's like the imx6
signaling this state by a hard wired gpio line because the soc and
cpu cores don't work properly on such low voltage values. This is
my use case and I can't use the sequencer.

Regards,
  Marco