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

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Date:	Wed, 22 Oct 2008 22:44:24 +0800
From:	Yu Zhao <yu.zhao@...scape.net>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
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'

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.

Thanks,
Yu
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