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

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Message-ID: <aCHXLarju7hOXL40@black.fi.intel.com>
Date: Mon, 12 May 2025 14:10:37 +0300
From: Raag Jadav <raag.jadav@...el.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Lee Jones <lee@...nel.org>, 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 Mon, May 12, 2025 at 12:36:24PM +0200, Greg KH wrote:
> On Mon, May 12, 2025 at 01:22:41PM +0300, Raag Jadav wrote:
> > 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?
> 
> I don't know what to say, I don't see the code here that is being
> quoted, sorry.  If this should be in the aux code, add it and submit a
> patch that uses it so we can see what you are referring to.
> 
> confused,

Apologies for snipping the context in attempt to reduce noise.

Original patch[1] with Lee's recommendation to move all the resource()
helpers from MFD to auxiliary subsystem, or perhaps an alternative way
to manage resources for the usecase.

[1] https://lore.kernel.org/r/20250428060207.3170325-1-raag.jadav@intel.com

I can still send out a v5 if it doesn't help. Let me know.

Raag