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

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Message-ID: <aBVArb-zJ_aqicHW@black.fi.intel.com>
Date: Sat, 3 May 2025 01:01:17 +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 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.

Raag