Re: [RFC PATCH 0/3] devicetree, qcomm PMIC: fix node name conflict

[Rob Herring]

On Tue, May 6, 2014 at 7:48 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote:
> An issue with the path of SPMI nodes under /sys/bus/... was reported in
> https://lkml.org/lkml/2014/4/23/312.  The symptom is that two different
> grandchild nodes of the spmi with the same node-name@unit-address will
> result in attempting to create duplicate links at
> /sys/bus/platform/devices/unit-address.node-name.  It turns out that the
> specific example provided might not be an expected configuration for
> current hardware, but the reported trap remains an issue.
>
> I have been poking at the problem, trying to figure out how to cleanly
> fix the issue without breaking devicetree device creation.
>
> The first patch in the series is the one that may be a very bad idea.  Or
> it may help show the way forward to deal with what I think is the major
> underlying problem.  I have not finished investigating the possible negative
> side effects.  And I am still thinking whether this is a conceptually good
> approach, or whether it is simply an expediant hack that hides the underlying
> problem.  But I am throwing this out prematurely because I have mentioned
> it to several people, and I want to make it visible to everyone involved.
>
> The underlying architectural problem (in my opinion) is that a lot of devices
> are created by the device tree infrastructure as platform devices, when they
> truly should not be platform devices.  They should not be platform devices
> because they are not physically on a platform bus, they are instead somewhere
> below some other bus.  The first patch in this series is a hack which
> results in the devices still being represented by "struct platform_device"
> objects, but with a link to their parent's "struct bus_type" instead of
> to &platform_bus_type.
>
> The second patch does not require the first patch.  The second patch provides
> a mechanism to allow subsystems to provide a method of naming devices to
> avoid name collisions.
>
> The third patch provides an example of a subsystem using the new feature
> provided by the second patch.
>

I think the primary question to ask is there any added benefit to
having the additional hierarchy of devices. I don't think there is
much support to have more hierarchy from what I have seen of past
discussions.

Another approach could be to support having multiple platform bus
instances. Then drivers can easily create a new instance for each set
of sub-devices.

This can be solved in a much less invasive way just in the DT naming
algorithm. This is slightly different from what I had suggested of
just dropping the unit address. It keeps the unit address, but adds
the unique index on untranslate-able addresses. The diff is bigger due
to refactoring to reduce the indentation levels. It is untested and
whitespace corrupted:

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 404d1da..c77dd7a 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -105,23 +105,33 @@ void of_device_make_bus_id(struct device *dev)
         * For MMIO, get the physical address
         */
        reg = of_get_property(node, "reg", NULL);
-       if (reg) {
-               if (of_can_translate_address(node)) {
-                       addr = of_translate_address(node, reg);
-               } else {
-                       addrp = of_get_address(node, 0, NULL, NULL);
-                       if (addrp)
-                               addr = of_read_number(addrp, 1);
-                       else
-                               addr = OF_BAD_ADDR;
-               }
-               if (addr != OF_BAD_ADDR) {
-                       dev_set_name(dev, "%llx.%s",
-                                    (unsigned long long)addr, node->name);
-                       return;
-               }
+       if (!reg)
+               goto no_bus_id;
+
+       if (of_can_translate_address(node)) {
+               addr = of_translate_address(node, reg);
+               if (addr == OF_BAD_ADDR)
+                       goto no_bus_id;
+
+               dev_set_name(dev, "%llx.%s",
+                            (unsigned long long)addr, node->name);
+               return;
        }

+       addrp = of_get_address(node, 0, NULL, NULL);
+       if (!addrp)
+               goto no_bus_id;
+
+       addr = of_read_number(addrp, 1);
+       if (addr == OF_BAD_ADDR)
+               goto no_bus_id;
+
+       magic = atomic_add_return(1, &bus_no_reg_magic);
+       dev_set_name(dev, "%llx.%s.%d", (unsigned long long)addr,
+                    node->name, magic - 1);
+       return;
+
+no_bus_id:
        /*
         * No BusID, use the node name and add a globally incremented
         * counter (and pray...)
--
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