On 04/04/2014 12:55 PM, Stephen Boyd wrote:
> On 04/03/14 19:18, Alex Elder wrote:
>> +
>> +/*
>> + * Secondary startup method setup routine to extract the location of
>> + * the secondary boot register from a "cpu" or "cpus" device tree
>> + * node. Only the first seen secondary boot register value is used;
>> + * any others are ignored. The secondary boot register value must be
>> + * non-zero.
>> + *
>> + * Returns 0 if successful or an error code otherwise.
>> + */
>> +static int __init of_enable_method_setup(struct device_node *node)
>> +{
>> + int ret;
>> +
>> + /* Ignore all but the first one specified */
>> + if (secondary_boot)
>> + return 0;
>> +
>> + ret = of_property_read_u32(node, OF_SECONDARY_BOOT, &secondary_boot);
>> + if (ret)
>> + pr_err("%s: missing/invalid " OF_SECONDARY_BOOT " property\n",
>> + node->name);
>> +
>> + return ret;
>> +}
>
> I don't understand why we need this. Why can't we get the secondary boot
> address from the /cpus node in the smp_prepare_cpus op. It isn't that
> hard to get access to the cpus node there via of_find_node_by_path().
> Then we don't need patch 1 at all. If it turns out to be common stuff,
> we can always have the common function live in arm common code or maybe
> even be a devicetree API.
I already responded to this, but never got any response. I
was preparing to re-send this series and wanted to try to
pull the added feature (patch 1) out and not be dependent on
it. But I think it's a bit ugly so I'm hoping to get a
blessing to proceed with what I originally proposed. For
reference, here's the thread:
https://lkml.org/lkml/2014/4/3/421
What I'm trying to do is get the value of a "secondary-boot-reg"
property from a node known to have an "enable-method" property
that matches the method name supplied in CPU_METHOD_OF_DECLARE().
Using the callback function as I originally proposed, this is
very easy. When arm_dt_init_cpu_maps() parses the "cpus" portion
of the device tree it calls set_smp_ops_by_method() for a
matching "cpu" or "cpus" node, and that function supplies
the node to the callback function. The callback can extract
additional property values if needed.
If I hold off until smp_prepare_cpus() is called, I have to
re-parse the device tree to find the "cpus" node (this is
in itself trivial). I then need to re-parse that node to
verify the matching "enable-method" property is found before
looking for the parameter information I need for that enable
method. I would really prefer not to re-do this parsing
step. It's imprecise and a little inefficient, and it
duplicates (but not exactly) logic that's already performed
by arm_dt_init_cpu_maps().
One more point of clarification. This "secondary-boot-reg"
value is *not* the secondary boot address--that is, it's
not the address secondary cores jump to when they are
activated. Instead, this is the address of a register
that's used to request the ROM code release a core from
its ROM-implemented holding pen. For this machine,
control jumps at that point to secondary_startup(),
defined in arch/arm/kernel/head.S.
So...
Stephen, I'd like to hear from you whether my explanation
is adequate, and whether you think my addition and use of
CPU_METHOD_OF_DECLARE_SETUP() is reasonable. (If you have
a suggestion for a better name, I'm open.)
If you still don't like it, I'll follow up with a
new version of the patches, this time parsing the
device tree in the smp_prepare_cpus() method as
you suggested. I don't want this to hold up getting
this SMP support into the kernel.
Thanks.
-Alex
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