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Subject: Re: Neophyte questions about PCIe
From: Mason <slash.tmp@free.fr>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci <linux-pci@vger.kernel.org>, Rob Herring <robh@kernel.org>,
 Ard Biesheuvel <ard.biesheuvel@linaro.org>,
 Thibaud Cornic <thibaud_cornic@sigmadesigns.com>,
 David Laight <david.laight@aculab.com>,
 Phuong Nguyen <phuong_nguyen@sigmadesigns.com>,
 Shawn Lin <shawn.lin@rock-chips.com>, Robin Murphy <robin.murphy@arm.com>,
 Linux ARM <linux-arm-kernel@lists.infradead.org>
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Date: Tue, 14 Mar 2017 16:54:00 +0100
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On 14/03/2017 15:00, Mason wrote:

> On 10/03/2017 18:49, Mason wrote:
> 
>> /* Root complex reports incorrect device class */
>> static void tango_pcie_fixup_class(struct pci_dev *dev)
>> {
>> 	dev->class = PCI_CLASS_BRIDGE_PCI << 8;
>> }
> 
> Gen1 controller reports class/rev = 0x04800001
> Gen2 controller reports class/rev = 0x06000001
> 
> #define PCI_CLASS_BRIDGE_HOST		0x0600
> #define PCI_CLASS_BRIDGE_ISA		0x0601
> #define PCI_CLASS_BRIDGE_EISA		0x0602
> #define PCI_CLASS_BRIDGE_MC		0x0603
> #define PCI_CLASS_BRIDGE_PCI		0x0604
> #define PCI_CLASS_BRIDGE_PCMCIA		0x0605
> #define PCI_CLASS_BRIDGE_NUBUS		0x0606
> #define PCI_CLASS_BRIDGE_CARDBUS	0x0607
> #define PCI_CLASS_BRIDGE_RACEWAY	0x0608
> #define PCI_CLASS_BRIDGE_OTHER		0x0680
> 
> My fixup replaces 0x048000 with 0x060400.
> 
> 	0x060400 != 0x060000
> 
> Which is correct:
> PCI_CLASS_BRIDGE_HOST or PCI_CLASS_BRIDGE_PCI?
> 
> Naively, I would expect Host/PCI bridge to be more correct
> for a root complex.

But that's very likely wrong, since the code in Linux does:

	switch (dev->hdr_type) {		    /* header type */
	case PCI_HEADER_TYPE_BRIDGE:		    /* bridge header */
		if (class != PCI_CLASS_BRIDGE_PCI)
			goto bad;
		/* The PCI-to-PCI bridge spec requires that subtractive
		   decoding (i.e. transparent) bridge must have programming
		   interface code of 0x01. */

So a class of PCI_CLASS_BRIDGE_HOST would error out, I think.
Does this mean I need to fixup Gen2 as well?
(Since it reports 0x060000)

Regards.