linux-kernel - Re: [patch 2/8] [Intel IOMMU] Some generic search functions required to lookup device relationships.

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Date:	Tue, 10 Apr 2007 21:36:37 -0700
From:	Greg KH <gregkh@...e.de>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Ashok Raj <ashok.raj@...el.com>, linux-kernel@...r.kernel.org,
	akpm@...l.org, ak@...e.de, muli@...ibm.com,
	asit.k.mallick@...el.com, suresh.b.siddha@...el.com,
	anil.s.keshavamurthy@...el.com, arjan@...ux.intel.com
Subject: Re: [patch 2/8] [Intel IOMMU] Some generic search functions
	required to lookup device relationships.

On Wed, Apr 11, 2007 at 09:40:36AM +0800, Shaohua Li wrote:
> On Tue, 2007-04-10 at 06:03 -0700, Greg KH wrote:
> > On Tue, Apr 10, 2007 at 04:11:38PM +0800, Shaohua Li wrote:
> > > On Mon, 2007-04-09 at 20:46 -0700, Greg KH wrote:
> > > > On Mon, Apr 09, 2007 at 02:55:54PM -0700, Ashok Raj wrote:
> > > > > +/*
> > > > > + * find the upstream PCIE-to-PCI bridge of a PCI device
> > > > > + * if the device is PCIE, return NULL
> > > > > + * if the device isn't connected to a PCIE bridge (that is its parent is a
> > > > > + * legacy PCI bridge and the bridge is directly connected to bus 0), return its
> > > > > + * parent
> > > > > + */
> > > > > +struct pci_dev *
> > > > > +pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
> > > > > +{
> > > > > +	struct pci_dev *tmp = NULL;
> > > > > +
> > > > > +	if (pdev->is_pcie)
> > > > > +		return NULL;
> > > > > +	while (1) {
> > > > > +		if (!pdev->bus->self)
> > > > > +			break;
> > > > > +		pdev = pdev->bus->self;
> > > > > +		/* a p2p bridge */
> > > > > +		if (!pdev->is_pcie) {
> > > > > +			tmp = pdev;
> > > > > +			continue;
> > > > > +		}
> > > > > +		/* PCI device should connect to a PCIE bridge */
> > > > > +		BUG_ON(pdev->pcie_type != PCI_EXP_TYPE_PCI_BRIDGE);
> > > > > +		return pdev;
> > > > > +	}
> > > > > +
> > > > > +	return tmp;
> > > > > +}
> > > > 
> > > > No locking while you walk up the bus list?
> > > hmm, iommu driver didn't support pci hotplug in current stage. But we
> > > can add lock here.
> > 
> > Please do, as PCI-E hotplug is much more common than PCI hotplug these
> > days (think ExpressCard in millions of laptops...)
> > 
> > > > > --- linux-2.6.21-rc5.orig/include/linux/pci.h	2007-04-03 04:30:51.000000000 -0700
> > > > > +++ linux-2.6.21-rc5/include/linux/pci.h	2007-04-03 06:58:58.000000000 -0700
> > > > > @@ -126,6 +126,7 @@
> > > > >  	unsigned short	subsystem_device;
> > > > >  	unsigned int	class;		/* 3 bytes: (base,sub,prog-if) */
> > > > >  	u8		hdr_type;	/* PCI header type (`multi' flag masked out) */
> > > > > +	u8		pcie_type;	/* PCI-E device/port type */
> > > > >  	u8		rom_base_reg;	/* which config register controls the ROM */
> > > > >  	u8		pin;  		/* which interrupt pin this device uses */
> > > > >  
> > > > > @@ -168,6 +169,7 @@
> > > > >  	unsigned int 	msi_enabled:1;
> > > > >  	unsigned int	msix_enabled:1;
> > > > >  	unsigned int	is_managed:1;
> > > > > +	unsigned int	is_pcie:1;
> > > > 
> > > > Do you really need both fields?  Wouldn't just the pcie_type one work
> > > > (with some NOT_PCIE type being set for it if it isn't I suppose.)
> > > There are some encodings are reserved for future. Just don't want to use
> > > reserved bits, as we don't know which one is proper for NOT_PCIE.
> > 
> > What are the current encodings?  I don't have my copy of the pci spec
> > availble at the moment...
> 0 - 1010b is defined. Other bits are reserved. How about the pcie_type's
> highest bit determines NOT_PCIE? the pcie spec just use 4 bits for pcie
> type.

No, nevermind, it's fine to use two variables, it would just be too
messy to put them in the same one with no real benifit.

thanks,

greg k-h
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