linux-kernel - Re: [PATCH 1/6] mfd: Add Delta TN48M CPLD driver

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Message-ID: <20210521090357.GD2549456@dell>
Date:   Fri, 21 May 2021 10:03:57 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Robert Marko <robert.marko@...tura.hr>
Cc:     Michael Walle <michael@...le.cc>, robh+dt@...nel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        bgolaszewski@...libre.com, jdelvare@...e.com,
        Guenter Roeck <linux@...ck-us.net>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-hwmon@...r.kernel.org, Luka Perkov <luka.perkov@...tura.hr>,
        jmp@...phyte.org, Paul Menzel <pmenzel@...gen.mpg.de>,
        Donald Buczek <buczek@...gen.mpg.de>
Subject: Re: [PATCH 1/6] mfd: Add Delta TN48M CPLD driver

On Fri, 21 May 2021, Robert Marko wrote:

> On Thu, May 20, 2021 at 8:49 AM Lee Jones <lee.jones@...aro.org> wrote:
> >
> > On Wed, 19 May 2021, Michael Walle wrote:
> >
> > > Hi,
> > >
> > > Am 2021-05-19 13:53, schrieb Robert Marko:
> > > > On Thu, May 6, 2021 at 6:34 PM Michael Walle <michael@...le.cc> wrote:
> > > > > Am 2021-04-30 14:35, schrieb Robert Marko:
> > > > > > Delta TN48M switches have a Lattice CPLD that serves
> > > > > > multiple purposes including being a GPIO expander.
> > > > > > So lets add the MFD core driver for it.
> > > > >
> > > > > Did you have a look at mfd/simple-mfd-i2c.c?
> > > >
> > > > Yes, that was my first idea but we have a requirement to expose CPLD
> > > > information via debugfs as there are userspace applications using it.
> > > > And simple-mfd-i2c does not allow us to do so.
> > >
> > > Mh, last time Lee wasn't very fond of having a driver that just populates
> > > sub-drivers while doing almost nothing itself. See
> > > https://lore.kernel.org/lkml/20200605065709.GD3714@dell/
> >
> > Right.  I still feel that way.
> >
> > > That being said, I'd also like to expose our CPLD version, but until now
> > > haven't found a good solution.
> >
> > Why though?  Does S/W *need* it?
> Because we have userspace S/W that uses it as the same CPLD is in
> multiple variants of the board but the correct board model is set during
> manufacturing and we can read it from the CPLD.
> 
> We also have information about PSU1 and PSU2(Some models only)
> power good, whether they are present and some other info that I need
> to expose as these are monitored in userspace.
> 
> I planned to do that via the hwmon driver but according to Guenther they
> are not hwmon attributes and I agree.
> 
> Would it be possible to have a dedicated driver that would only expose
> the required information via debugfs?
> Then I could simply use the simple I2C MFD driver with only a GPIO
> driver on top of it.

Yes, I was going to suggest that.

It should probably live in drivers/misc.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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