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

Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> · Tue, 15 Aug 2017 15:01:48 +0800

Hi Bjorn,

On 2017/8/12 5:17, Bjorn Helgaas wrote:
[+cc Lorenzo, resending because I fat-fingered the cc line and subject]

On Tue, Jun 27, 2017 at 08:31:13AM +0800, Shawn Lin wrote:
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@xxxxxxxxxxxxxx>

The "use_dt_domains" logic in of_pci_bus_find_domain_nr() is fairly
obtuse.  I *think*, now that we have pci_scan_root_bus_bridge() due to
Lorenzo's excellent work, the time is ripe for moving the domain
number from arch-specific places into struct pci_host_bridge.

I suspect that will end up simplifying the CONFIG_PCI_DOMAINS vs
CONFIG_PCI_DOMAINS_GENERIC situation, and I wonder whether it might
enable some simplification of of_pci_bus_find_domain_nr() as well,
which in turn, might make *this* patch simpler.

This isn't that big a patch to begin with, so I could apply it as-is
and we could do more domain cleanup later.  It's just that it's
intertwined with the PCI_DOMAINS #ifdefs and maybe there's an
opportunity to make this story more readable if those are out of the
way.  Any thoughts?

That sounds good to me that aftering add IDA domain, we could start
considering moving domain number from arch-specific places into the
bridge code and may be could also finally remove the macro
CONFIG_PCI_DOMAIN* both?


---

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












