linux-kernel - RE: [PATCH 03/10] PCI: AMD SATA IDE mode quirk

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Date:	Mon, 25 Feb 2008 09:43:59 +0800
From:	"Cai, Crane" <Crane.Cai@....com>
To:	"Matthew Wilcox" <matthew@....cx>
Cc:	"Greg Kroah-Hartman" <gregkh@...e.de>,
	<linux-pci@...ey.karlin.mff.cuni.cz>,
	<linux-kernel@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Andrew Morton" <akpm@...l.org>
Subject: RE: [PATCH 03/10] PCI: AMD SATA IDE mode quirk

> On Fri, Feb 22, 2008 at 01:49:20PM +0800, Cai, Crane wrote:
> > > On Thu, Feb 21, 2008 at 03:47:33PM -0800, Greg 
> Kroah-Hartman wrote:
> > > > +static void __devinit quirk_amd_ide_mode(struct pci_dev *pdev)
> > > >  {
> > > > -	/* set sb600 sata to ahci mode */
> > > > -	if ((pdev->class >> 8) == PCI_CLASS_STORAGE_IDE) {
> > > > -		u8 tmp;
> > > > +	/* set sb600/sb700/sb800 sata to ahci mode */
> > > > +	u8 tmp;
> > > >  
> > > > +	pci_read_config_byte(pdev, PCI_CLASS_DEVICE, &tmp);
> > > > +	if (tmp == 0x01) {
> > > >  		pci_read_config_byte(pdev, 0x40, &tmp);
> > > 
> > > This seems like a dis-improvement.  Why are we reading a 
> config byte 
> > > for something we already have in the pci_dev?
> > > Why are we now checking against 0x01 instead of a 
> symbolic constant?  
> > > Why are we no longer checking that this is PCI_BASE_CLASS_STORAGE?
> > It is a quirk. In pci_ids.h did have PCI_CLASS_STORAGE_IDE and 
> > PCI_BASE_CLASS_STORAGE, these can not represent the right 
> situation we 
> > want to check. 0x01 represents PCI_CLASS_STORAGE_IDE last 2 
> bit. Also 
> > because it is a quirk, I do not think we need to change 
> pci_ids.h. So 
> > 0x01 used.
> 
> You haven't explained what is wrong with the original code:
> 
> 	if ((pdev->class >> 8) == PCI_CLASS_STORAGE_IDE) {
> 

When resume, this pdev->class is quirked, however BIOS has modified pci configuration too. Inconsistance occurs.

> > > Nothing in the changelog entry suggests why we now need 
> FIXUP_RESUME 
> > > entries when we didn't before.
> > > 
> > PCI configuration space will be changed by BIOS and then in 
> pci init 
> > and restore. So resume also needed.
> 
> That information needed to be in the changelog.

This info, is a normal info. If maintainer need us to added in source code. I preferred too. 
> --
> Intel are signing my paycheques ... these opinions are still 
> mine "Bill, look, we understand that you're interested in 
> selling us this operating system, but compare it to ours.  We 
> can't possibly take such a retrograde step."
> 
> 
> 

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