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Subject[RFC PATCH v2, part 2 01/18] PCI: introduce hotplug-safe PCI bus iterators
Date
Introduce hotplug-safe PCI bus iterators as below, which hold a
reference on the returned PCI bus object.
bool pci_bus_exists(int domain, int busnr);
struct pci_bus *pci_get_bus(int domain, int busnr);
struct pci_bus *pci_get_next_bus(struct pci_bus *from);
struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
#define for_each_pci_bus(b) for (b = NULL; (b = pci_get_next_bus(b)); )
#define for_each_pci_root_bus(b) \
for (b = NULL; (b = pci_get_next_root_bus(b)); )

The long-term goal is to remove hotplug-unsafe pci_find_bus(),
pci_find_next_bus() and the global pci_root_buses list.

These new interfaces may be a littler slower than existing interfaces,
but it should be acceptable because they are not used on hot paths.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
drivers/pci/pci.h | 1 +
drivers/pci/probe.c | 2 +-
drivers/pci/search.c | 159 +++++++++++++++++++++++++++++++++++++++++----------
include/linux/pci.h | 23 +++++++-
4 files changed, 153 insertions(+), 32 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 68678ed..8fe15f6 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -126,6 +126,7 @@ static inline void pci_remove_legacy_files(struct pci_bus *bus) { return; }

/* Lock for read/write access to pci device and bus lists */
extern struct rw_semaphore pci_bus_sem;
+extern struct class pcibus_class;

extern raw_spinlock_t pci_lock;

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index e59433a..6b77333 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -93,7 +93,7 @@ static void release_pcibus_dev(struct device *dev)
kfree(pci_bus);
}

-static struct class pcibus_class = {
+struct class pcibus_class = {
.name = "pci_bus",
.dev_release = &release_pcibus_dev,
.dev_attrs = pcibus_dev_attrs,
diff --git a/drivers/pci/search.c b/drivers/pci/search.c
index d0627fa..16ccaf8 100644
--- a/drivers/pci/search.c
+++ b/drivers/pci/search.c
@@ -52,20 +52,27 @@ pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
return tmp;
}

-static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
+struct pci_bus_match_arg {
+ int domain;
+ int bus;
+};
+
+static int pci_match_bus(struct device *dev, const void *data)
{
- struct pci_bus* child;
- struct list_head *tmp;
+ struct pci_bus *bus = to_pci_bus(dev);
+ const struct pci_bus_match_arg *arg = data;

- if(bus->number == busnr)
- return bus;
+ return (pci_domain_nr(bus) == arg->domain && bus->number == arg->bus);
+}

- list_for_each(tmp, &bus->children) {
- child = pci_do_find_bus(pci_bus_b(tmp), busnr);
- if(child)
- return child;
- }
- return NULL;
+static int pci_match_next_bus(struct device *dev, const void *data)
+{
+ return 1;
+}
+
+static int pci_match_next_root_bus(struct device *dev, const void *data)
+{
+ return pci_is_root_bus(to_pci_bus(dev));
}

/**
@@ -76,20 +83,19 @@ static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
* Given a PCI bus number and domain number, the desired PCI bus is located
* in the global list of PCI buses. If the bus is found, a pointer to its
* data structure is returned. If no bus is found, %NULL is returned.
+ *
+ * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
+ * Please use pci_get_bus() instead which holds a reference on the returned
+ * PCI bus.
*/
-struct pci_bus * pci_find_bus(int domain, int busnr)
+struct pci_bus *pci_find_bus(int domain, int busnr)
{
- struct pci_bus *bus = NULL;
- struct pci_bus *tmp_bus;
+ struct pci_bus *bus;

- while ((bus = pci_find_next_bus(bus)) != NULL) {
- if (pci_domain_nr(bus) != domain)
- continue;
- tmp_bus = pci_do_find_bus(bus, busnr);
- if (tmp_bus)
- return tmp_bus;
- }
- return NULL;
+ bus = pci_get_bus(domain, busnr);
+ pci_bus_put(bus);
+
+ return bus;
}

/**
@@ -100,21 +106,114 @@ struct pci_bus * pci_find_bus(int domain, int busnr)
* initiated by passing %NULL as the @from argument. Otherwise if
* @from is not %NULL, searches continue from next device on the
* global list.
+ *
+ * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
+ * Please use pci_get_next_root_bus() instead which holds a reference
+ * on the returned PCI root bus.
*/
struct pci_bus *
pci_find_next_bus(const struct pci_bus *from)
{
- struct list_head *n;
- struct pci_bus *b = NULL;
+ struct device *dev = from ? (struct device *)&from->dev : NULL;
+
+ dev = class_find_device(&pcibus_class, dev, NULL,
+ &pci_match_next_root_bus);
+ if (dev) {
+ put_device(dev);
+ return to_pci_bus(dev);
+ }
+
+ return NULL;
+}
+
+bool pci_bus_exists(int domain, int busnr)
+{
+ struct device *dev;
+ struct pci_bus_match_arg arg = { domain, busnr };

WARN_ON(in_interrupt());
- down_read(&pci_bus_sem);
- n = from ? from->node.next : pci_root_buses.next;
- if (n != &pci_root_buses)
- b = pci_bus_b(n);
- up_read(&pci_bus_sem);
- return b;
+ dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
+ if (dev)
+ put_device(dev);
+
+ return dev != NULL;
+}
+EXPORT_SYMBOL(pci_bus_exists);
+
+/**
+ * pci_get_bus - locate PCI bus from a given domain and bus number
+ * @domain: number of PCI domain to search
+ * @busnr: number of desired PCI bus
+ *
+ * Given a PCI bus number and domain number, the desired PCI bus is located.
+ * If the bus is found, a pointer to its data structure is returned.
+ * If no bus is found, %NULL is returned.
+ * Caller needs to release the returned bus by calling pci_bus_put().
+ */
+struct pci_bus *pci_get_bus(int domain, int busnr)
+{
+ struct device *dev;
+ struct pci_bus_match_arg arg = { domain, busnr };
+
+ WARN_ON(in_interrupt());
+ dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
+ if (dev)
+ return to_pci_bus(dev);
+
+ return NULL;
+}
+EXPORT_SYMBOL(pci_get_bus);
+
+/**
+ * pci_get_next_bus - begin or continue searching for a PCI bus
+ * @from: Previous PCI bus found, or %NULL for new search.
+ *
+ * Iterates through the list of known PCI busses. If a PCI bus is found,
+ * the reference count to the bus is incremented and a pointer to it is
+ * returned. Otherwise, %NULL is returned. A new search is initiated by
+ * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
+ * searches continue from next bus on the global list. The reference count
+ * for @from is always decremented if it is not %NULL.
+ */
+struct pci_bus *pci_get_next_bus(struct pci_bus *from)
+{
+ struct device *dev = from ? &from->dev : NULL;
+
+ WARN_ON(in_interrupt());
+ dev = class_find_device(&pcibus_class, dev, NULL, &pci_match_next_bus);
+ pci_bus_put(from);
+ if (dev)
+ return to_pci_bus(dev);
+
+ return NULL;
+}
+EXPORT_SYMBOL(pci_get_next_bus);
+
+/**
+ * pci_find_next_root_bus - begin or continue searching for a PCI root bus
+ * @from: Previous PCI bus found, or %NULL for new search.
+ *
+ * Iterates through the list of known PCI root busses. If a PCI bus is found,
+ * the reference count to the root bus is incremented and a pointer to it is
+ * returned. Otherwise, %NULL is returned. A new search is initiated by
+ * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
+ * searches continue from next root bus on the global list. The reference
+ * count for @from is always decremented if it is not %NULL.
+ */
+struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
+{
+ struct device *dev = from ? &from->dev : NULL;
+
+ WARN_ON(in_interrupt());
+ dev = class_find_device(&pcibus_class, dev, NULL,
+ &pci_match_next_root_bus);
+ pci_bus_put(from);
+ if (dev)
+ return to_pci_bus(dev);
+
+ return NULL;
}
+EXPORT_SYMBOL(pci_get_next_root_bus);

/**
* pci_get_slot - locate PCI device for a given PCI slot
diff --git a/include/linux/pci.h b/include/linux/pci.h
index cc4ce27..c88d4e6 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -454,6 +454,9 @@ struct pci_bus {

#define pci_bus_b(n) list_entry(n, struct pci_bus, node)
#define to_pci_bus(n) container_of(n, struct pci_bus, dev)
+#define for_each_pci_bus(b) for (b = NULL; (b = pci_get_next_bus(b)); )
+#define for_each_pci_root_bus(b) \
+ for (b = NULL; (b = pci_get_next_root_bus(b)); )

/*
* Returns true if the pci bus is root (behind host-pci bridge),
@@ -718,7 +721,6 @@ void pcibios_resource_to_bus(struct pci_dev *dev, struct pci_bus_region *region,
void pcibios_bus_to_resource(struct pci_dev *dev, struct resource *res,
struct pci_bus_region *region);
void pcibios_scan_specific_bus(int busn);
-struct pci_bus *pci_find_bus(int domain, int busnr);
void pci_bus_add_devices(const struct pci_bus *bus);
struct pci_bus * __deprecated pci_scan_bus_parented(struct device *parent,
int bus, struct pci_ops *ops, void *sysdata);
@@ -778,8 +780,15 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap);
int pci_find_next_ext_capability(struct pci_dev *dev, int pos, 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_bus(int domain, int busnr);
struct pci_bus *pci_find_next_bus(const struct pci_bus *from);

+bool pci_bus_exists(int domain, int busnr);
+struct pci_bus *pci_get_bus(int domain, int busnr);
+struct pci_bus *pci_get_next_bus(struct pci_bus *from);
+struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
+
struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
struct pci_dev *from);
struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
@@ -1429,6 +1438,18 @@ static inline void pci_unblock_cfg_access(struct pci_dev *dev)
static inline struct pci_bus *pci_find_next_bus(const struct pci_bus *from)
{ return NULL; }

+static inline bool pci_bus_exists(int domain, int busnr)
+{ return false; }
+
+static inline struct pci_bus *pci_get_bus(int domain, int busnr)
+{ return NULL; }
+
+static inline struct pci_bus *pci_get_next_bus(struct pci_bus *from)
+{ return NULL; }
+
+static inline struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
+{ return NULL; }
+
static inline struct pci_dev *pci_get_slot(struct pci_bus *bus,
unsigned int devfn)
{ return NULL; }
--
1.8.1.2


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