[Skiboot] [RFC 07/12] core/pci: Add for_each_pci_dev()

[Oliver O'Halloran]

Add an interation helper for PCI devices. This is functionally identical
to the pci_walk_devs() helper function, but it allows us to write linear
code rather than dropping us into the middle of callback hell.

Signed-off-by: Oliver O'Halloran <oohall at gmail.com>
---
 core/pci.c    | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/pci.h |  9 +++++++
 2 files changed, 93 insertions(+)

diff --git a/core/pci.c b/core/pci.c
index 4296180ad111..c5d2fba36508 100644
--- a/core/pci.c
+++ b/core/pci.c
@@ -1798,6 +1798,90 @@ static struct pci_device *__pci_walk_dev(struct phb *phb,
 	return NULL;
 }
 
+/*
+ * pci_next_dev(phb, prev, pass) - Iteration worker function
+ *
+ * phb  - phb that we're iterating
+ * prev - the last pci_device returned by pci_next_dev
+ *
+ * pass - a cookie used to track the iteration state. See below if you
+ *        really want to know the details.
+ */
+struct pci_device *pci_next_dev(struct phb *phb, struct pci_device *prev,
+				int *pass)
+{
+	struct pci_device *next, *last;
+	struct list_head *siblings;
+
+	assert(phb);
+
+	/* start of iteration */
+	if (!prev) {
+		*pass = 0;
+		return list_top(&phb->devices, struct pci_device, link);
+	}
+
+up:
+	assert(prev);
+
+	if (prev->parent)
+		siblings = &prev->parent->children;
+	else
+		siblings = &phb->devices;
+
+	last = list_tail(siblings, struct pci_device, link);
+	assert(last);
+
+	/*
+	 * You made it this far so you get an explaination!
+	 *
+	 * We need to ensure that the iteration order is correct, that is we are
+	 * supposed to look at each *device* on a bus before looking at the
+	 * *child buses* below those devices, as is done in pci_walk_devs(). In
+	 * other words, we do two pases of every bus.
+	 *
+	 * The 'pass' variable is used to track which pass we are on. When it's
+	 * even we are just visiting each device and when odd we are descending
+	 * into child buses if we find any.
+	 */
+	if (prev == last) {
+		if (*pass & 1) { /* end of the odd pass */
+			if (!prev->parent) {
+				assert(*pass == 1);
+				return NULL;
+			}
+
+			/* back to the odd pass across the parent's bus */
+			(*pass) -= 2;
+			prev = prev->parent;
+			goto up;
+		} else {
+			next = list_top(siblings, struct pci_device, link);
+			(*pass)++;
+		}
+	} else {
+		next = list_entry(prev->link.next, struct pci_device, link);
+	}
+
+	/* now find the device we should return */
+	if (!(*pass & 1))
+		return next;
+
+	/* for an odd pass we scan for another child bus to descend into */
+	while (list_empty(&next->children)) {
+		if (next == last) {
+			prev = last;
+			goto up;
+		}
+
+		next = list_entry(next->link.next, struct pci_device, link);
+	}
+
+	/* increment pass so it's even */
+	(*pass)++;
+	return list_top(&next->children, struct pci_device, link);
+}
+
 struct pci_device *pci_walk_dev(struct phb *phb,
 				struct pci_device *pd,
 				int (*cb)(struct phb *,
diff --git a/include/pci.h b/include/pci.h
index f216594c42cf..78f82939c9b6 100644
--- a/include/pci.h
+++ b/include/pci.h
@@ -456,6 +456,15 @@ static inline struct phb *__pci_next_phb_idx(uint64_t *phb_id) {
 	for (uint64_t __phb_idx = 0;				\
 	     (phb = __pci_next_phb_idx(&__phb_idx)) ; )
 
+
+struct pci_device *pci_next_dev(struct phb *phb, struct pci_device *pd, int *pass);
+
+/* pass should be an int *, see pci_next_dev() for details */
+#define for_each_pci_dev(phb, pd, pass) \
+	for (pd = pci_next_dev(phb, NULL, pass); \
+		pd; \
+		pd = pci_next_dev(phb, pd, pass))
+
 /* Device tree */
 extern void pci_std_swizzle_irq_map(struct dt_node *dt_node,
 				    struct pci_device *pd,
-- 
2.9.4