linux-kernel - Re: [PATCH 2/16 v6] PCI: define PCI resource names in an 'enum'

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Date:	Wed, 22 Oct 2008 08:51:11 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Yu Zhao <yu.zhao@...scape.net>
Cc:	Yu Zhao <yu.zhao@...el.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"achiang@...com" <achiang@...com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"greg@...ah.com" <greg@...ah.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"matthew@....cx" <matthew@....cx>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 2/16 v6] PCI: define PCI resource names in an 'enum'

On Wednesday 22 October 2008 08:44:24 am Yu Zhao wrote:
> Bjorn Helgaas wrote:
> > On Wednesday 22 October 2008 02:40:41 am Yu Zhao wrote:
> >> This patch moves all definitions of the PCI resource names to an 'enum',
> >> and also replaces some hard-coded resource variables with symbol
> >> names. This change eases introduction of device specific resources.
> > 
> > Thanks for removing a bunch of magic numbers from the code.
> > 
> >>  static void
> >>  pci_restore_bars(struct pci_dev *dev)
> >>  {
> >> -	int i, numres;
> >> -
> >> -	switch (dev->hdr_type) {
> >> -	case PCI_HEADER_TYPE_NORMAL:
> >> -		numres = 6;
> >> -		break;
> >> -	case PCI_HEADER_TYPE_BRIDGE:
> >> -		numres = 2;
> >> -		break;
> >> -	case PCI_HEADER_TYPE_CARDBUS:
> >> -		numres = 1;
> >> -		break;
> >> -	default:
> >> -		/* Should never get here, but just in case... */
> >> -		return;
> >> -	}
> >> +	int i;
> >>  
> >> -	for (i = 0; i < numres; i++)
> >> +	for (i = 0; i < PCI_BRIDGE_RESOURCES; i++)
> >>  		pci_update_resource(dev, i);
> >>  }
> > 
> > The behavior of this function used to depend on dev->hdr_type.  Now
> > we don't look at hdr_type at all, so we do the same thing for all
> > devices.
> > 
> > For example, for a CardBus device, we used to call pci_update_resource()
> > only for BAR 0; now we call it for BARs 0-6.
> > 
> > Maybe this is safe, but I can't tell from the patch, so I think you
> > should explain *why* it's safe in the changelog.
> 
> It's safe because pci_update_resource() will ignore unused resources. 
> E.g., for a Cardbus, only BAR 0 is used and its 'flags' is set, then 
> pci_update_resource() only updates it. BAR 1-6 are ignored since their 
> 'flags' are 0.
> 
> I'll put more explanation in the changelog.

This is a logically separate change from merely substituting enum
names for magic numbers, so you might even consider splitting it
into a separate patch.  Better bisection and all that, you know :-)

Bjorn
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