linux-kernel - Re: [PATCH V15 6/9] mfd: pm8008: Use i2c_new_dummy

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Message-ID: <Yzwb2e0/CK9QbV0n@google.com>
Date:   Tue, 4 Oct 2022 12:41:13 +0100
From:   Lee Jones <lee@...nel.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Satya Priya Kakitapalli <quic_c_skakit@...cinc.com>,
        Mark Brown <broonie@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_collinsd@...cinc.com,
        quic_subbaram@...cinc.com, quic_jprakash@...cinc.com
Subject: Re: [PATCH V15 6/9] mfd: pm8008: Use i2c_new_dummy_device() API

On Mon, 03 Oct 2022, Stephen Boyd wrote:

> Quoting Lee Jones (2022-09-29 11:01:41)
> > On Wed, 28 Sep 2022, Stephen Boyd wrote:
> >
> > > Quoting Lee Jones (2022-09-28 03:20:30)
> > > > Wouldn't it make more sense to simply separate the instantiation of
> > > > the 2 I2C devices?  Similar to what you suggested [0] in v9.  That way
> > > > they can handle their own resources and we can avoid all of the I2C
> > > > dummy / shared Regmap passing faff.
> > > >
> > > > [0] https://lore.kernel.org/all/CAE-0n53G-atsuwqcgNvi3nvWyiO3P=pSj5zDUMYj0ELVYJE54Q@mail.gmail.com/
> > > >
> > >
> > > You can continue reading the thread[1]. My understanding is it's one
> > > chip that responds on two i2c addresses, thus we don't describe that as
> > > two i2c device nodes in DT. Instead we describe one node and use the
> > > dummy API to make the second i2c device.
> > >
> > > [1] https://lore.kernel.org/all/Yk3NkNK3e+fgj4eG@sirena.org.uk/
> >
> > As Mark says, it's probably 2 separate dies that have been encased in
> > the same IC and are otherwise unconnected.  Not sure I understand the
> > comment about not requiring another 'struct device'.  It will still
> > require that whether it's a platform device or an I2C device, right?
> >
> 
> Yes a 'struct device' will be required for each i2c address no matter
> what happens.
> 
> It is also useful to describe the hardware as one device node in case
> there is a shared reset signal or power supply. That allows us to have
> one driver probe the DT node and deassert the reset/power the chip on. I
> think this device has one reset signal, so we really need to do this and
> not treat them as completely independent i2c devices (the 0x8 and 0x9
> addresses).
> 
> Can we move forward with my plan to have another i2c device made for
> 'pm8008-regulators' and have that driver be an i2c driver that probes an
> i2c device manually created in the pm8008 driver? I think that would
> handle the reset ordering problem because the pm8008 driver can deassert
> the reset and also handle the regmap passing stuff by letting the i2c
> device at 0x9 make its own regmap.

Sure, why not.  I'm pretty done talking about this now. :)

Please work with Satya to cobble something together.

-- 
Lee Jones [李琼斯]