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

From: Robert Marko <robert.marko@sartura.hr>
To: Lee Jones <lee.jones@linaro.org>
Cc: Michael Walle <michael@walle.cc>,
	robh+dt@kernel.org, Linus Walleij <linus.walleij@linaro.org>,
	bgolaszewski@baylibre.com, jdelvare@suse.com,
	Guenter Roeck <linux@roeck-us.net>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-gpio@vger.kernel.org, linux-hwmon@vger.kernel.org,
	Luka Perkov <luka.perkov@sartura.hr>,
	jmp@epiphyte.org, Paul Menzel <pmenzel@molgen.mpg.de>,
	Donald Buczek <buczek@molgen.mpg.de>
Subject: Re: [PATCH 1/6] mfd: Add Delta TN48M CPLD driver
Date: Fri, 21 May 2021 11:06:44 +0200	[thread overview]
Message-ID: <CA+HBbNH9BMbV9G_Emc4qfoKkdK3YYRmY16cNd_Hu5h1Ch0wctw@mail.gmail.com> (raw)
In-Reply-To: <20210521090357.GD2549456@dell>

On Fri, May 21, 2021 at 11:04 AM Lee Jones <lee.jones@linaro.org> wrote:
>
> On Fri, 21 May 2021, Robert Marko wrote:
>
> > On Thu, May 20, 2021 at 8:49 AM Lee Jones <lee.jones@linaro.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@walle.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.

OK, that works for me.
I will then rework this for v2.

Regards,
Robert
>
> --
> Lee Jones [李琼斯]
> Senior Technical Lead - Developer Services
> Linaro.org │ Open source software for Arm SoCs
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-- 
Robert Marko
Staff Embedded Linux Engineer
Sartura Ltd.
Lendavska ulica 16a
10000 Zagreb, Croatia
Email: robert.marko@sartura.hr
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