linux-kernel - Re: [PATCH v4] mfd: core: Support auxiliary device

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Message-ID: <aCHL8WWV-Wt7OrII@black.fi.intel.com>
Date: Mon, 12 May 2025 13:22:41 +0300
From: Raag Jadav <raag.jadav@...el.com>
To: Lee Jones <lee@...nel.org>, gregkh@...uxfoundation.org
Cc: david.m.ertman@...el.com, ira.weiny@...el.com,
	andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
	heikki.krogerus@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mfd: core: Support auxiliary device

On Sat, May 03, 2025 at 01:01:23AM +0300, Raag Jadav wrote:
> On Thu, May 01, 2025 at 01:50:28PM +0100, Lee Jones wrote:
> > On Mon, 28 Apr 2025, Raag Jadav wrote:
> > 
> > > Extend MFD subsystem to support auxiliary child device. This is useful
> > > for MFD usecases where parent device is on a discoverable bus and doesn't
> > > fit into the platform device criteria. Purpose of this implementation is
> > > to provide discoverable MFDs just enough infrastructure to register
> > > independent child devices without abusing the platform device.
> > > 
> > > Current support is limited to just PCI type MFDs, but this can be further
> > > extended to support other types like USB in the future.
> > > 
> > > Signed-off-by: Raag Jadav <raag.jadav@...el.com>
> > > ---
> > > 
> > > v2: Introduce a shared struct mfd_aux_device
> > >     Introduce auxiliary device opt-in flag
> > > 
> > > v3: Fix device_type ABI breakage (Andy)
> > >     Aesthetic adjustments (Andy)
> > > 
> > > v4: s/mfd_aux/maux
> > >     Allow num_resources for child device (Andy)
> > >     Fix build warning (Andy)
> > > 
> > >  drivers/mfd/Kconfig      |   2 +-
> > >  drivers/mfd/Makefile     |   2 +-
> > >  drivers/mfd/mfd-aux.c    | 156 +++++++++++++++++++++++++++++++
> > 
> > This looks like mostly duplicated platform device code.
> > 
> > If you are _certain_ that it needs to exist, you need to push it out to
> > the auxiliary subsystem and remove any traces of it being MFD related.
> > 
> > If it's needed by MFD, it'll be needed by other auxiliary users.  Even
> > if not now, sometime in the future.
> 
> Greg, if you are okay with this, please let me know. Or perhaps suggest
> a better alternative.

Greg, any guidance on this?

Raag