PCI: Refactor capability search into PCI_FIND_NEXT_CAP()

The PCI Capability search functionality is duplicated across the PCI core
and several controller drivers. The core's current implementation requires
fully initialized PCI device and bus structures, which prevents controller
drivers from using it during early initialization phases before these
structures are available.

Move the Capability search logic into a PCI_FIND_NEXT_CAP() macro that
accepts a config space accessor function as an argument. This enables
controller drivers to perform Capability discovery using their early
access mechanisms prior to full device initialization while sharing the
Capability search code.

Convert the existing PCI core Capability search implementation to use
PCI_FIND_NEXT_CAP().  Controller drivers can later use this with their
early access mechanisms while maintaining the existing protection against
infinite loops through preserved TTL checks.

Signed-off-by: Hans Zhang <18255117159@163.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Link: https://patch.msgid.link/20250813144529.303548-3-18255117159@163.com

1 files changed, 8 insertions, 34 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 40a5c87d9a6b..ac2658d946ea 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -9,7 +9,6 @@
  */
 
 #include <linux/acpi.h>
-#include <linux/align.h>
 #include <linux/kernel.h>
 #include <linux/delay.h>
 #include <linux/dmi.h>
@@ -424,36 +423,10 @@ found:
 	return 1;
 }
 
-static u8 __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
-				  u8 pos, int cap, int *ttl)
-{
-	u8 id;
-	u16 ent;
-
-	pci_bus_read_config_byte(bus, devfn, pos, &pos);
-
-	while ((*ttl)--) {
-		if (pos < PCI_STD_HEADER_SIZEOF)
-			break;
-		pos = ALIGN_DOWN(pos, 4);
-		pci_bus_read_config_word(bus, devfn, pos, &ent);
-
-		id = FIELD_GET(PCI_CAP_ID_MASK, ent);
-		if (id == 0xff)
-			break;
-		if (id == cap)
-			return pos;
-		pos = FIELD_GET(PCI_CAP_LIST_NEXT_MASK, ent);
-	}
-	return 0;
-}
-
 static u8 __pci_find_next_cap(struct pci_bus *bus, unsigned int devfn,
 			      u8 pos, int cap)
 {
-	int ttl = PCI_FIND_CAP_TTL;
-
-	return __pci_find_next_cap_ttl(bus, devfn, pos, cap, &ttl);
+	return PCI_FIND_NEXT_CAP(pci_bus_read_config, pos, cap, bus, devfn);
 }
 
 u8 pci_find_next_capability(struct pci_dev *dev, u8 pos, int cap)
@@ -649,7 +622,7 @@ EXPORT_SYMBOL_GPL(pci_get_dsn);
 
 static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
 {
-	int rc, ttl = PCI_FIND_CAP_TTL;
+	int rc;
 	u8 cap, mask;
 
 	if (ht_cap == HT_CAPTYPE_SLAVE || ht_cap == HT_CAPTYPE_HOST)
@@ -657,8 +630,8 @@ static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
 	else
 		mask = HT_5BIT_CAP_MASK;
 
-	pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn, pos,
-				      PCI_CAP_ID_HT, &ttl);
+	pos = PCI_FIND_NEXT_CAP(pci_bus_read_config, pos,
+				PCI_CAP_ID_HT, dev->bus, dev->devfn);
 	while (pos) {
 		rc = pci_read_config_byte(dev, pos + 3, &cap);
 		if (rc != PCIBIOS_SUCCESSFUL)
@@ -667,9 +640,10 @@ static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
 		if ((cap & mask) == ht_cap)
 			return pos;
 
-		pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn,
-					      pos + PCI_CAP_LIST_NEXT,
-					      PCI_CAP_ID_HT, &ttl);
+		pos = PCI_FIND_NEXT_CAP(pci_bus_read_config,
+					pos + PCI_CAP_LIST_NEXT,
+					PCI_CAP_ID_HT, dev->bus,
+					dev->devfn);
 	}
 
 	return 0;