PCI: Add pci_find_ht_capability() for finding Hypertransport capabilities

There are already several places in the kernel that want to search a PCI
device for a given Hypertransport capability. Although this is possible
using pci_find_capability() etc., it makes sense to encapsulate that
logic in a helper - pci_find_ht_capability().

To cater for searching exhaustively for a capability, we also provide
pci_find_next_ht_capability().

We also need to cater for the fact that the HT capability fields may be
either 3 or 5 bits wide. pci_find_ht_capability() deals with this for you,
but callers using the #defines directly must handle that themselves.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/pci/pci.c

@@ -68,12 +68,14 @@ pci_max_busnr(void)
 
 #endif  /*  0  */
 
-static int __pci_find_next_cap(struct pci_bus *bus, unsigned int devfn, u8 pos, int cap)
+#define PCI_FIND_CAP_TTL	48
+
+static int __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
+				   u8 pos, int cap, int *ttl)
 {
 	u8 id;
-	int ttl = 48;
 
-	while (ttl--) {
+	while ((*ttl)--) {
 		pci_bus_read_config_byte(bus, devfn, pos, &pos);
 		if (pos < 0x40)
 			break;
@@ -89,6 +91,14 @@ static int __pci_find_next_cap(struct pci_bus *bus, unsigned int devfn, u8 pos,
 	return 0;
 }
 
+static int __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);
+}
+
 int pci_find_next_capability(struct pci_dev *dev, u8 pos, int cap)
 {
 	return __pci_find_next_cap(dev->bus, dev->devfn,
@@ -224,6 +234,74 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 }
 EXPORT_SYMBOL_GPL(pci_find_ext_capability);
 
+static int __pci_find_next_ht_cap(struct pci_dev *dev, int pos, int ht_cap)
+{
+	int rc, ttl = PCI_FIND_CAP_TTL;
+	u8 cap, mask;
+
+	if (ht_cap == HT_CAPTYPE_SLAVE || ht_cap == HT_CAPTYPE_HOST)
+		mask = HT_3BIT_CAP_MASK;
+	else
+		mask = HT_5BIT_CAP_MASK;
+
+	pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn, pos,
+				      PCI_CAP_ID_HT, &ttl);
+	while (pos) {
+		rc = pci_read_config_byte(dev, pos + 3, &cap);
+		if (rc != PCIBIOS_SUCCESSFUL)
+			return 0;
+
+		if ((cap & mask) == ht_cap)
+			return pos;
+
+		pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn, pos,
+					      PCI_CAP_ID_HT, &ttl);
+	}
+
+	return 0;
+}
+/**
+ * pci_find_next_ht_capability - query a device's Hypertransport capabilities
+ * @dev: PCI device to query
+ * @pos: Position from which to continue searching
+ * @ht_cap: Hypertransport capability code
+ *
+ * To be used in conjunction with pci_find_ht_capability() to search for
+ * all capabilities matching @ht_cap. @pos should always be a value returned
+ * from pci_find_ht_capability().
+ *
+ * NB. To be 100% safe against broken PCI devices, the caller should take
+ * steps to avoid an infinite loop.
+ */
+int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap)
+{
+	return __pci_find_next_ht_cap(dev, pos + PCI_CAP_LIST_NEXT, ht_cap);
+}
+EXPORT_SYMBOL_GPL(pci_find_next_ht_capability);
+
+/**
+ * pci_find_ht_capability - query a device's Hypertransport capabilities
+ * @dev: PCI device to query
+ * @ht_cap: Hypertransport capability code
+ *
+ * Tell if a device supports a given Hypertransport capability.
+ * Returns an address within the device's PCI configuration space
+ * or 0 in case the device does not support the request capability.
+ * The address points to the PCI capability, of type PCI_CAP_ID_HT,
+ * which has a Hypertransport capability matching @ht_cap.
+ */
+int pci_find_ht_capability(struct pci_dev *dev, int ht_cap)
+{
+	int pos;
+
+	pos = __pci_bus_find_cap_start(dev->bus, dev->devfn, dev->hdr_type);
+	if (pos)
+		pos = __pci_find_next_ht_cap(dev, pos, ht_cap);
+
+	return pos;
+}
+EXPORT_SYMBOL_GPL(pci_find_ht_capability);
+
 /**
  * pci_find_parent_resource - return resource region of parent bus of given region
  * @dev: PCI device structure contains resources to be searched

include/linux/pci.h

@@ -454,6 +454,8 @@ struct pci_dev *pci_find_slot (unsigned int bus, unsigned int devfn);
 int pci_find_capability (struct pci_dev *dev, int cap);
 int pci_find_next_capability (struct pci_dev *dev, u8 pos, int cap);
 int pci_find_ext_capability (struct pci_dev *dev, int cap);
+int pci_find_ht_capability (struct pci_dev *dev, int ht_cap);
+int pci_find_next_ht_capability (struct pci_dev *dev, int pos, int ht_cap);
 struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
 
 struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,

include/linux/pci_regs.h

@@ -475,9 +475,19 @@
 #define PCI_PWR_CAP		12	/* Capability */
 #define  PCI_PWR_CAP_BUDGET(x)	((x) & 1)	/* Included in system budget */
 
-/* Hypertransport sub capability types */
+/*
+ * Hypertransport sub capability types
+ *
+ * Unfortunately there are both 3 bit and 5 bit capability types defined
+ * in the HT spec, catering for that is a little messy. You probably don't
+ * want to use these directly, just use pci_find_ht_capability() and it
+ * will do the right thing for you.
+ */
+#define HT_3BIT_CAP_MASK	0xE0
 #define HT_CAPTYPE_SLAVE	0x00	/* Slave/Primary link configuration */
 #define HT_CAPTYPE_HOST		0x20	/* Host/Secondary link configuration */
+
+#define HT_5BIT_CAP_MASK	0xF8
 #define HT_CAPTYPE_IRQ		0x80	/* IRQ Configuration */
 #define HT_CAPTYPE_REMAPPING_40	0xA0	/* 40 bit address remapping */
 #define HT_CAPTYPE_REMAPPING_64 0xA2	/* 64 bit address remapping */