netdev - Re: [RFC 01/32] Kconfig: introduce and depend on LEGACY

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Date:   Tue, 28 Dec 2021 10:15:16 +0100
From:   Mauro Carvalho Chehab <mchehab@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        John Garry <john.garry@...wei.com>,
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Subject: Re: [RFC 01/32] Kconfig: introduce and depend on LEGACY_PCI

Em Tue, 28 Dec 2021 09:21:23 +0100
Greg Kroah-Hartman <gregkh@...uxfoundation.org> escreveu:

> On Mon, Dec 27, 2021 at 05:42:46PM +0100, Niklas Schnelle wrote:
> > --- a/drivers/pci/Kconfig
> > +++ b/drivers/pci/Kconfig
> > @@ -23,6 +23,17 @@ menuconfig PCI
> >  
> >  if PCI
> >  
> > +config LEGACY_PCI
> > +	bool "Enable support for legacy PCI devices"
> > +	depends on HAVE_PCI
> > +	help
> > +	   This option enables support for legacy PCI devices. This includes
> > +	   PCI devices attached directly or via a bridge on a PCI Express bus.
> > +	   It also includes compatibility features on PCI Express devices which
> > +	   make use of legacy I/O spaces.  

This Kconfig doesn't seem what it is needed there, as this should be an 
arch-dependent feature, and not something that the poor user should be
aware if a given architecture supports it or not. Also, the above will keep
causing warnings or errors with randconfigs.

Also, the "depends on HAVE_CPI" is bogus, as PCI already depends on 
HAVE_PCI:

	menuconfig PCI
	bool "PCI support"
	depends on HAVE_PCI
	help
	  This option enables support for the PCI local bus, including
	  support for PCI-X and the foundations for PCI Express support.
	  Say 'Y' here unless you know what you are doing.

So, instead, I would expect that a new HAVE_xxx option would be
added at arch/*/Kconfig, like:

	config X86
		...
		select HAVE_PCI_DIRECT_IO

It would also make sense to document it at Documentation/features/.

> 
> All you really care about is the "legacy" I/O spaces here, this isn't
> tied to PCI specifically at all, right?
> 
> So why not just have a OLD_STYLE_IO config option or something like
> that, to show that it's the i/o functions we care about here, not PCI at
> all?
> 
> And maybe not call it "old" or "legacy" as time constantly goes forward,
> just describe it as it is, "DIRECT_IO"?

Agreed. HAVE_PCI_DIRECT_IO (or something similar) seems a more appropriate
name for it.

Thanks,
Mauro