Message-ID: <CAHp75VdiH=J-ovCdh1RFJDW_bJM8=pbXRaHmB691GLb-5oBmYQ@mail.gmail.com>
Date:   Mon, 8 Jun 2020 13:02:21 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Lee Jones <lee.jones@...aro.org>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        david.m.ertman@...el.com, shiraz.saleem@...el.com
Cc:     Michael Walle <michael@...le.cc>, Rob Herring <robh+dt@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hwmon@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller

+Cc: some Intel people WRT our internal discussion about similar
problem and solutions.

On Mon, Jun 8, 2020 at 11:30 AM Lee Jones <lee.jones@...aro.org> wrote:
> On Sat, 06 Jun 2020, Michael Walle wrote:
> > Am 2020-06-06 13:46, schrieb Mark Brown:
> > > On Fri, Jun 05, 2020 at 10:07:36PM +0200, Michael Walle wrote:
> > > > Am 2020-06-05 12:50, schrieb Mark Brown:

...

> Right.  I'm suggesting a means to extrapolate complex shared and
> sometimes intertwined batches of register sets to be consumed by
> multiple (sub-)devices spanning different subsystems.
>
> Actually scrap that.  The most common case I see is a single Regmap
> covering all child-devices.

Yes, because often we need a synchronization across the entire address
space of the (parent) device in question.

>  It would be great if there was a way in
> which we could make an assumption that the entire register address
> space for a 'tagged' (MFD) device is to be shared (via Regmap) between
> each of the devices described by its child-nodes.  Probably by picking
> up on the 'simple-mfd' compatible string in the first instance.
>
> Rob, is the above something you would contemplate?
>
> Michael, do your register addresses overlap i.e. are they intermingled
> with one another?  Do multiple child devices need access to the same
> registers i.e. are they shared?
>
> > > > But, there is more in my driver:
> > > >  (1) there is a version check
>
> If we can rid the Regmap dependency, then creating an entire driver to
> conduct a version check is unjustifiable.  This could become an inline
> function which is called by each of the sub-devices instead, for
> example.
>
> > > >  (2) there is another function for which there is no suitable linux
> > > >      subsystem I'm aware of and thus which I'd like to us sysfs
> > > >      attributes for: This controller supports 16 non-volatile
> > > >      configuration bits. (this is still TBD)
>
> There is a place for everything in Linux.
>
> What do these bits configure?
>
> > > TBH I'd also say that the enumeration of the subdevices for this
> > > device should be in the device rather than the DT, they don't
> > > seem to be things that exist outside of this one device.
> >
> > We're going circles here, formerly they were enumerated in the MFD.
> > Yes, they are devices which aren't likely be used outside a
> > "sl28cpld", but there might there might be other versions of the
> > sl28cpld with other components on different base addresses. I
> > don't care if they are enumerated in DT or MFD, actually, I'd
> > prefer the latter. _But_ I would like to have the device tree
> > properties for its subdevices, e.g. the ones for the watchdog or
> > whatever components there might be in the future.
>
> [...]
>
> > MFD core can
> > match a device tree node today; but only one per unique compatible
> > string. So what should I use to differentiate the different
> > subdevices?
>
> Right.  I have been aware of this issue.  The only suitable solution
> to this would be to match on 'reg'.
>
> FYI: I plan to fix this.
>
> If your register map needs to change, then I suggest that this is
> either a new device or at least a different version of the device and
> would also have to be represented as different (sub-)mfd_cell.
>
> > Rob suggested the internal offset, which I did here.
>
> FWIW, I don't like this idea.  DTs should not have to be modified
> (either in the first instance or subsequently) or specifically
> designed to patch inadequacies in any given OS.
>
> > But then, there is less use in duplicating the offsets in the MFD
> > just to have the MFD enumerate the subdevices and then match
> > the device tree nodes against it. I can just use
> > of_platform_populate() to enumerate the children and I won't
> > have to duplicate the base addresses.
>
> Which is fine.  However this causes a different issue for you.  By
> stripping out the MFD code you render the MFD portion seemingly
> superfluous.  Another issue driver authors commonly contend with.

-- 
With Best Regards,
Andy Shevchenko

Powered by blists - more mailing lists