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[pci] Avoid scanning nonexistent buses when using PCIAPI_DIRECT

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There is no method for obtaining the number of PCI buses when using
PCIAPI_DIRECT, and we therefore currently scan all possible bus
numbers.  This can cause a several-second startup delay in some
virtualised environments, since PCI configuration space access will
necessarily require the involvement of the hypervisor.

Ameliorate this situation by defaulting to scanning only a single bus,
and expanding the number of PCI buses to accommodate any subordinate
buses that are detected during enumeration.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2021-04-10 13:14:30 +01:00
parent c0346dbb49
commit 0be8491b71
3 changed files with 30 additions and 4 deletions
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4
src/arch/x86/include/ipxe/pcidirect.h
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@@ -32,8 +32,8 @@ extern void pcidirect_prepare ( struct pci_device *pci, int where );
*/
static inline __always_inline int
PCIAPI_INLINE ( direct, pci_num_bus ) ( void ) {
/* No way to work this out via Type 1 accesses */
return 0x100;
/* Scan first bus and rely on bridge detection to find higher buses */
return 1;
}
/**