linux-kernel - Re: [PATCH v1] mfd: core: Support auxiliary device

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Message-ID: <2025040343-vascular-swung-f124@gregkh>
Date: Thu, 3 Apr 2025 15:23:22 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Raag Jadav <raag.jadav@...el.com>, david.m.ertman@...el.com,
	ira.weiny@...el.com, lee@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mfd: core: Support auxiliary device

On Thu, Apr 03, 2025 at 05:19:22PM +0300, Andy Shevchenko wrote:
> On Thu, Apr 03, 2025 at 05:16:51PM +0300, Andy Shevchenko wrote:
> > On Thu, Apr 03, 2025 at 03:02:47PM +0100, Greg KH wrote:
> > > On Thu, Apr 03, 2025 at 04:30:53PM +0530, Raag Jadav wrote:
> 
> ...
> 
> > > > 2. Should we allow auxiliary drivers to manage their own resources
> > > >    (MEM, IO, IRQ etc)?
> > > 
> > > The resources are all shared by the "parent" device, that's what makes
> > > aux drivers work, they need to handle this as there is no unique way to
> > > carve up the resources here.
> > > 
> > > So I don't know how you would do this, sorry.
> > 
> > I think we should simply enforce the requirement that MFD on AUX bus must use
> > regmap. This will solve the serialisation and common access to the resources.
> 
> That said, make an additional API call like
> 
> dev_mfd_add_aux_devices() which should enforce new infrastructure and convert
> drivers one by one. Also with that you may add a warning to the existing (PCI)
> drivers that are using old API
> 
> 	if (dev_is_pci(parent))
> 		dev_warn(parent, "Uses old API, please switch to ...\n");

Don't add "warnings" like this if you aren't also going to actually
convert the code.  Just convert it, otherwise you pester users with
problems that they have no idea how to fix.

thanks,

greg k-h