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

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Message-ID: <Z-6bzTC5UMMFLS6S@black.fi.intel.com>
Date: Thu, 3 Apr 2025 17:31:41 +0300
From: Raag Jadav <raag.jadav@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, 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 05:26:34PM +0300, Andy Shevchenko wrote:
> On Thu, Apr 03, 2025 at 03:23:22PM +0100, Greg KH wrote:
> > 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.
> 
> Good point. I'm wondering how many actually we have PCI MFD (ab)users right
> now? 30? 100? More?

$ git grep "struct pci_driver" drivers/mfd/ | wc -l
12

Raag