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

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Date:	Mon, 25 Feb 2008 00:31:00 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
To:	"Cai, Crane" <Crane.Cai@....com>
Cc:	Matthew Wilcox <matthew@....cx>,
	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 Mon, Feb 25, 2008 at 09:43:59AM +0800, Cai, Crane wrote:
> > 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.

Can you update pdev->class from the quirk?
It would be consistent then.
That would leave the code as-is except it's re-reading the field
from config space.

hth,
grant

> > > > 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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