[XenPPC] Location to hook setting ppc_md.enable_pmcs for xen

[Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>]

How does the inclusion of the code in the subdir platform/xen work in 
xenppc-linux - Does it replace the bare metal code in platform/pseries 
or does it "extend" it in any way? Xen has has at least a completely own 
define_machine section there so I assume "replace".
The issue is that I ask myself if I should add something like:
a) in function "pSeries_setup_arch" of 
"arch/powerpc/platforms/pseries/setup.c"
    ...
+   if (?XEN?)
+       ppc_md.enable_pmcs = pseries_xen_enable_pmcs;
m   else if (firmware_has_feature(FW_FEATURE_LPAR))
        ppc_md.enable_pmcs = pseries_lpar_enable_pmcs;
    else
        ppc_md.enable_pmcs = power4_enable_pmcs;
    ...

or

b) go to the xen path and do this in function "xen_setup_arch" of 
"arch/powerpc/platforms/xen/setup.c"
with something like this:
    ...
        xen_setup_smp();
    #endif

+        ppc_md.enable_pmcs = pseries_xen_enable_pmcs;

        printk(KERN_INFO "Using Xen idle loop\n");
    ...

According to the Makefile of "arch/powerpc/plattforms" both are build 
anyway.
As far as I read it in the code the platform is detected at boot time 
and the
appropriate ppc_md structure gets selected which should be the only xen 
structure in our case.
This would argue for variant b) to implement it in 
"arch/powerpc/platforms/xen/*"
Can someone with more experience in that area please send an ack for b) 
or correct me?
--

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt@xxxxxxxxxxxxxxxxxxx
Ehrhardt@xxxxxxxxxx

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