At Fri, 15 Aug 2003 23:01:21 +0000 (UTC), "M. Warner Losh" wrote:
> : If you read that back as vendor ID, no, you *cannot* have a function 1.
> 
> Where does the standard state that, exactly?

That literally, it doesn't.


> I'll grant that the sun
> hme device is an extreme edge case, but it appears to comply with the
> standard, at least 'a reading of the standard might imply that it
> complies.'

Don't think so, because it returns an invalid ID.

> Vendor ID     This field identifies the manufacturer of the device. Valid
>               vendor identifiers are allocated by the PCI SIG to ensure
>               uniqueness. 0FFFFh is an invalid value for Vendor ID.

Invalid != Sun.


> The standard doesn't say the device can't have a vendor-id
> of 0xffff, just that that vendor id will not be assigned and can be
> considered to be invalid.  But what "invalid" means is only by
> implication, not explicitly stated.  Does it mean 'the whole device is
> not there?' or 'this function is not there?'
> 
> Here's the quoted areas:
> 
> 6.2.1 says:
> Vendor ID: ... Valid vendor identifiers are allocated by the PCI SIG
> to ensure uniqueness.  0FFFFh is an invalid value for the Vendor
> ID.[1]

Except, you skip the "This field identifies the manufacturer of the
device" bit.

Invalid != Sun.


> section 6.1 says:
> System software may need to scan the bus to determine what devices are
> actually present.  To do this, the configuration software must read
> the Vendor ID in each possible PCI "slot."  The host bus to PCI must
> unambiguously report attempts to read the Vendor ID of non-existant
> devices.  Since 0FFFFh is an invalid Vendor ID, it is adequate for the
> host bus to PCI bridge to return a value of all 1's on read access to
> Configuration Space of non-existant devices.[2]
> 
> [1] there's no implication as to what invalid means for the bigger
> picture in this section.
> 
> [2] notice that this says 'invalid devices will return 0xffff' and not
> the contrapositive that 'no device may return 0xffff' except by
> implication.

No, I think logic gets you that from "No vendor == Invalid".  8-)




cgd