[PATCH] powerpc: Add missing error check to prom_find_boot_cpu()

[Darren Stevens <darren@stevens-zone.net>]

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prom_init.c calls 'instance-to-package' twice, but the return
is not checked during prom_find_boot_cpu(). The result is then
passed to prom_getprop, which could be PROM_ERROR.
Add a return check to prevent this.

This was found on a pasemi system, where CFE doesn't have a working
'instance-to package' prom call.
Before Commit 5c0484e25ec0 ('powerpc: Endian safe trampoline') the
area around addr 0 as mostly 0's and this doesn't cause a problem.
Once the macro 'FIXUP_ENDIAN' has been added to head_64.S, the low
memory area now has non-zero values, which cause the prom_getprop
call to hang.

Signed-off-by: Darren Stevens <darren@stevens-zone.net>

---

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diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index ec47a93..ac83eb0 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -2834,6 +2834,9 @@ static void __init prom_find_boot_cpu(void)
 
 	cpu_pkg = call_prom("instance-to-package", 1, 1, prom_cpu);
 
+	if (!PHANDLE_VALID(cpu_pkg))
+		return;
+
 	prom_getprop(cpu_pkg, "reg", &rval, sizeof(rval));
 	prom.cpu = be32_to_cpu(rval);