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a _BBN value of 0 if it was for the first bridge encountered since some older systems returned _BBN of 0 for all bridges. However, some newer systems enumerate bridges with non-zero _BBN before bus 0 which is perfectly valid. Handle both cases by trusting the first bridge that has a _BBN of 0 and falling back to reading from non-standard config registers only for subsequent bridges with a _BBN of 0. We also only perform this check for segment (domain) 0. We assume that _BBN is always correct for segments other than 0. Tested by: Josef Moellers josef.moellers at fujitsu MFC after: 1 week