linux-kernel - RE: [PATCH RESEND 1/3] PCI: Add fwnode_handle to pci

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Message-ID: <DM2PR0301MB123298B3233B172BA2C92EF4ABD00@DM2PR0301MB1232.namprd03.prod.outlook.com>
Date:	Wed, 3 Feb 2016 22:42:00 +0000
From:	Jake Oshins <jakeo@...rosoft.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <helgaas@...nel.org>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	KY Srinivasan <kys@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH RESEND 1/3] PCI: Add fwnode_handle to pci_sysdata

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier@....com]
> Sent: Wednesday, February 3, 2016 10:57 AM
> To: Bjorn Helgaas <helgaas@...nel.org>; Jake Oshins
> <jakeo@...rosoft.com>
> Cc: gregkh@...uxfoundation.org; KY Srinivasan <kys@...rosoft.com>; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; Haiyang Zhang
> <haiyangz@...rosoft.com>; bhelgaas@...gle.com; linux-
> pci@...r.kernel.org
> Subject: Re: [PATCH RESEND 1/3] PCI: Add fwnode_handle to pci_sysdata
> 
> On 03/02/16 18:51, Bjorn Helgaas wrote:
> > On Wed, Feb 03, 2016 at 06:32:20PM +0000, Jake Oshins wrote:
> >>> -----Original Message-----
> >>> From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> >>> Sent: Wednesday, February 3, 2016 10:25 AM
> >>> To: Jake Oshins <jakeo@...rosoft.com>
[snip]
> >>>>
> >>>> +#ifndef pci_root_bus_fwnode
> >>>> +#define pci_root_bus_fwnode(bus)	((void)(bus), NULL)
> >>>
> >>> Huh, interesting.  This is new for me; I guess the idea is that we at least
> >>> evaluate "bus" even when pci_root_bus_fwnode isn't defined, so the
> >>> compiler can catch egregious errors?
> >>>
> >>
> >> This was a suggestion by Mark Zyngier.  It made the non-x86 architectures
> build benignly.  If you'd like it done differently, I'm open to suggestion.
> 
> I don't remember suggesting the use of the comma operator, but just to
> check that pci_root_bus_fwnode wasn't previously defined.
> 
> > Something like "#define pci_root_bus_fwnode(bus) NULL" would be
> > typical.  What I'm curious about is the use of the comma operator.
> > I'm not opposed to it; I'm just trying to understand why it makes a
> > difference.
> 
> I guess it flags the variable as used, and prevents an overly sensitive
> compiler from being loud and obnoxious... Just a guess though.
> 
> 	M.
> --

I was just copying the form that was in the code that Marc pointed out, somewhere else.  I have no particular attachment to this construct.  Honestly, since I'm still relatively new to the Linux codebase, I just assumed that was a common form that I should follow suit on.  If you tell me that the simpler NULL is more typical, I prefer that.  I'll simplify this when I resend the patch series.

Thanks,
Jake