Hi Michael,
Thanks for pointing out the issue. My mistake...
This patch should indeed make sense only when
CONFIG_PHYS_64BIT=y

I could not find corenet32_smp_defconfig, but I guess in your config,
CONFIG_PHYS_64BIT=n ?
I will update the patch later today

On Sun, Dec 22, 2019 at 5:38 PM Michael Ellerman [off-list ref] wrote:

yingjie_bai@126.com writes:

quoted

From: Bai Yingjie <redacted>

CPU like P4080 has 36bit physical address, its DDR physical
start address can be configured above 4G by LAW registers.

For such systems in which their physical memory start address was
configured higher than 4G, we need also to write addr_h into the spin
table of the target secondary CPU, so that addr_h and addr_l together
represent a 64bit physical address.
Otherwise the secondary core can not get correct entry to start from.

This should do no harm for normal case where addr_h is all 0.

Signed-off-by: Bai Yingjie <redacted>
---
 arch/powerpc/platforms/85xx/smp.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
index 8c7ea2486bc0..f12cdd1e80ff 100644
--- a/arch/powerpc/platforms/85xx/smp.c
+++ b/arch/powerpc/platforms/85xx/smp.c

@@ -252,6 +252,14 @@ static int smp_85xx_start_cpu(int cpu)
      out_be64((u64 *)(&spin_table->addr_h),
              __pa(ppc_function_entry(generic_secondary_smp_init)));
 #else
+     /*
+      * We need also to write addr_h to spin table for systems
+      * in which their physical memory start address was configured
+      * to above 4G, otherwise the secondary core can not get
+      * correct entry to start from.
+      * This does no harm for normal case where addr_h is all 0.
+      */
+     out_be32(&spin_table->addr_h, __pa(__early_start) >> 32);
      out_be32(&spin_table->addr_l, __pa(__early_start));

This breaks the corenet32_smp_defconfig build:

  /linux/arch/powerpc/platforms/85xx/smp.c: In function 'smp_85xx_start_cpu':
  /linux/arch/powerpc/platforms/85xx/smp.c:262:52: error: right shift count >= width of type [-Werror=shift-count-overflow]
    262 |  out_be32(&spin_table->addr_h, __pa(__early_start) >> 32);
        |                                                    ^~
  cc1: all warnings being treated as errors

cheers