[pci] Separate permission to probe buses from bus:dev.fn range discovery

The UEFI device model requires us to not probe the PCI bus directly,
but instead to wait to be offered the opportunity to drive devices via
our driver service binding handle.

We currently inhibit PCI bus probing by having pci_discover() return
an empty range when using the EFI PCI I/O API.  This has the unwanted
side effect that scanning the bus manually using the "pciscan" command
will also fail to discover any devices.

Separate out the concept of being allowed to probe PCI buses from the
mechanism for discovering PCI bus:dev.fn address ranges, so that this
limitation may be removed.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/ecam.h

@@ -54,6 +54,16 @@ struct ecam_mapping {
 	int rc;
 };
 
+/**
+ * Check if PCI bus probing is allowed
+ *
+ * @ret ok		Bus probing is allowed
+ */
+static inline __always_inline int
+PCIAPI_INLINE ( ecam, pci_can_probe ) ( void ) {
+	return 1;
+}
+
 extern struct pci_api ecam_api;
 
 #endif /* _IPXE_ECAM_H */

src/include/ipxe/efi/efi_pci_api.h

@@ -32,6 +32,16 @@ extern int efipci_read ( struct pci_device *pci, unsigned long location,
 extern int efipci_write ( struct pci_device *pci, unsigned long location,
 			  unsigned long value );
 
+/**
+ * Check if PCI bus probing is allowed
+ *
+ * @ret ok		Bus probing is allowed
+ */
+static inline __always_inline int
+PCIAPI_INLINE ( efi, pci_can_probe ) ( void ) {
+	return 0;
+}
+
 /**
  * Find next PCI bus:dev.fn address range in system
  *

src/include/ipxe/linux/linux_pci.h

@@ -22,6 +22,16 @@ extern int linux_pci_read ( struct pci_device *pci, unsigned long where,
 extern int linux_pci_write ( struct pci_device *pci, unsigned long where,
 			     unsigned long value, size_t len );
 
+/**
+ * Check if PCI bus probing is allowed
+ *
+ * @ret ok		Bus probing is allowed
+ */
+static inline __always_inline int
+PCIAPI_INLINE ( linux, pci_can_probe ) ( void ) {
+	return 1;
+}
+
 /**
  * Find next PCI bus:dev.fn address range in system
  *

src/include/ipxe/pci_io.h

@@ -66,6 +66,13 @@ struct pci_range {
 /* Include all architecture-dependent I/O API headers */
 #include <bits/pci_io.h>
 
+/**
+ * Check if PCI bus probing is allowed
+ *
+ * @ret ok		Bus probing is allowed
+ */
+int pci_can_probe ( void );
+
 /**
  * Find next PCI bus:dev.fn address range in system
  *