[PATCH v5] PCI: use IDA to manage domain number if not getting it from DT

[Shawn Lin <shawn.lin@rock-chips.com>]

If not getting domain number from DT, the domain number will
keep increasing once doing unbind/bind RC drivers. This could
introduce pointless tree view of lspci as shows below:

-+-[0001:00]---00.0-[01]----00.0
  \-[0000:00]-

The more test we do, the lengthier it would be. The more serious
issue is that if attaching two hierarchies for two different domains
belonging to two root bridges, so when doing unbind/bind test for one
of them and keep the other, then the domain number would finally
overflow and make the two hierarchies of devices share the some domain
number but actually they shouldn't. So it looks like we need to invent
a new indexing ID mechanism to manage domain number. This patch
introduces idr to achieve our purpose.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>

---

Changes in v5:
- fix Bjorn's comments for v3 as actually I didn't address his comments
  for v3 when posted my v4.
  v3: https://patchwork.kernel.org/patch/9742003/
  For ACPI case, we never use DT or IDA to get domain numbers and
  acpi_pci_bus_find_domain_nr would return the proper value we need
  whether _SEG exist or not. For DT or IDA, we hope bridges use one of
  them consistently, and this is actually what the pre-existing code
  did. So I remove ida_domain now since it complicated the logic of the
  code and we could just make use_dt_domains global instead to slightly
  achieve our purpose.

Changes in v4:
- make domain_nr depends on CONFIG_PCI_DOMAINS instead of
CONFIG_PCI_DOMAINS_GENERIC.

Changes in v3:
- make ida_domain a system-wide property and check it in the code to
combine with use_dt_domains. Also update the comment there.

Changes in v2:
- add a remove wrapper
- rename use_dt_domains to ida_domain and set this bit
in pci_get_new_domain_nr and test it in the remove wrapper.

 drivers/pci/pci.c    | 13 ++++++++++---
 drivers/pci/remove.c |  2 ++
 include/linux/pci.h  |  7 +++++--
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b58a6b3..9953eaf 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -11,6 +11,7 @@
 #include <linux/kernel.h>
 #include <linux/delay.h>
 #include <linux/dmi.h>
+#include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/of.h>
 #include <linux/of_pci.h>
@@ -5305,17 +5306,23 @@ static void pci_no_domains(void)
 }
 
 #ifdef CONFIG_PCI_DOMAINS
-static atomic_t __domain_nr = ATOMIC_INIT(-1);
+static DEFINE_IDA(__domain_nr);
 
 int pci_get_new_domain_nr(void)
 {
-	return atomic_inc_return(&__domain_nr);
+	return ida_simple_get(&__domain_nr, 0, sizeof(u64), GFP_KERNEL);
+}
+
+static int use_dt_domains = -1;
+void pci_put_domain_nr(struct pci_bus *bus)
+{
+	if (acpi_disabled && use_dt_domains != 1)
+		ida_simple_remove(&__domain_nr, bus->domain_nr);
 }
 
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 static int of_pci_bus_find_domain_nr(struct device *parent)
 {
-	static int use_dt_domains = -1;
 	int domain = -1;
 
 	if (parent)
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index 73a03d3..01dd1b4 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -157,6 +157,8 @@ void pci_remove_root_bus(struct pci_bus *bus)
 	list_for_each_entry_safe(child, tmp,
 				 &bus->devices, bus_list)
 		pci_remove_bus_device(child);
+
+	pci_put_domain_nr(bus);
 	pci_remove_bus(bus);
 	host_bridge->bus = NULL;
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 18cc70a..d6be9596 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -523,7 +523,7 @@ struct pci_bus {
 	unsigned char	primary;	/* number of primary bridge */
 	unsigned char	max_bus_speed;	/* enum pci_bus_speed */
 	unsigned char	cur_bus_speed;	/* enum pci_bus_speed */
-#ifdef CONFIG_PCI_DOMAINS_GENERIC
+#ifdef CONFIG_PCI_DOMAINS
 	int		domain_nr;
 #endif
 
@@ -1466,11 +1466,14 @@ static inline int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 #ifdef CONFIG_PCI_DOMAINS
 extern int pci_domains_supported;
 int pci_get_new_domain_nr(void);
+void pci_put_domain_nr(struct pci_bus *bus);
 #else
 enum { pci_domains_supported = 0 };
 static inline int pci_domain_nr(struct pci_bus *bus) { return 0; }
 static inline int pci_proc_domain(struct pci_bus *bus) { return 0; }
-static inline int pci_get_new_domain_nr(void) { return -ENOSYS; }
+static inline int pci_get_new_domain_nr(void)
+{ return -ENOSYS; }
+static inline void pci_put_domain_nr(struct pci_bus *bus) { }
 #endif /* CONFIG_PCI_DOMAINS */
 
 /*
-- 
1.9.1