On Mon, Sep 8, 2014 at 9:54 AM, Liviu Dudau [off-list ref] wrote:

On Mon, Sep 08, 2014 at 03:27:56PM +0100, Rob Herring wrote:

quoted

On Mon, Sep 8, 2014 at 8:54 AM, Liviu Dudau [off-list ref] wrote:

quoted

Add of_pci_get_domain_nr() to retrieve the PCI domain number
of a given device from DT. If the information is not present,
the function can be requested to allocate a new domain number.

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
---
 drivers/of/of_pci.c    | 34 ++++++++++++++++++++++++++++++++++
 include/linux/of_pci.h |  7 +++++++
 2 files changed, 41 insertions(+)

diff --git a/drivers/of/of_pci.c b/drivers/of/of_pci.c
index 8481996..a107edb 100644
--- a/drivers/of/of_pci.c
+++ b/drivers/of/of_pci.c

@@ -89,6 +89,40 @@ int of_pci_parse_bus_range(struct device_node *node, struct resource *res)
 }
 EXPORT_SYMBOL_GPL(of_pci_parse_bus_range);

+static atomic_t of_domain_nr = ATOMIC_INIT(-1);
+
+/**
+ * This function will try to obtain the host bridge domain number by
+ * using of_alias_get_id() call with "pci-domain" as a stem. If that
+ * fails, a local allocator will be used. The local allocator can
+ * be requested to return a new domain_nr if the information is missing
+ * from the device tree.
+ *
+ * @node: device tree node with the domain information
+ * @allocate_if_missing: if DT lacks information about the domain nr,
+ * allocate a new number.
+ *
+ * Returns the associated domain number from DT, or a new domain number
+ * if DT information is missing and @allocate_if_missing is true. If
+ * @allocate_if_missing is false then the last allocated domain number
+ * will be returned.
+ */
+int of_pci_get_domain_nr(struct device_node *node, bool allocate_if_missing)
+{
+       int domain;
+
+       domain = of_alias_get_id(node, "pci-domain");
+       if (domain == -ENODEV) {
+               if (allocate_if_missing)
+                       domain = atomic_inc_return(&of_domain_nr);
+               else
+                       domain = atomic_read(&of_domain_nr);

This function seems a bit broken to me. It is overloaded with too many
different outcomes. Think about how this would work if you have
multiple PCI buses and a mixture of having pci-domain aliases or not.
Aren't domain numbers global? Allocation should then start outside of
the range of alias ids.

Rob

Rob,

Would this version make more sense?

No.

int of_pci_get_domain_nr(struct device_node *node, bool allocate_if_missing)
{
       int domain;

       domain = of_alias_get_id(node, "pci-domain");
       if (domain == -ENODEV) {
               if (allocate_if_missing)
                       domain = atomic_inc_return(&of_domain_nr);
               else
                       domain = atomic_read(&of_domain_nr);
       } else {
               /* remember the largest value seen */
               int d = atomic_read(&of_domain_nr);
               atomic_set(&of_domain_nr, max(domain, d));
       }

       return domain;
}
EXPORT_SYMBOL_GPL(of_pci_get_domain_nr);

It would still create gaps and possible duplicates, but this is just a number
and trying to create a new root bus in an existing domain should fail. I have

Is failure okay in that case?

no clue on how to generate unique values without parsing the DT and filling
a sparse array with values found there and then checking for allocated values

You really only need to know the maximum value and then start the
non-DT allocations from there.

on new requests. This function gets called quite a lot and I'm trying not to
make it too heavy weight.

Generally, nothing should be accessing the same DT value frequently.
It should get cached somewhere.

I don't really understand how domains are used so it's hard to provide
a recommendation here. Do domains even belong in the DT? This function
is just a weird mixture of data retrieval and allocation. I think you
need to separate it into 2 functions.

Rob