Hi, Jiaxun,

On Fri, Jan 8, 2021 at 6:15 PM Jiaxun Yang [off-list ref] wrote:

在 2021/1/8 下午6:07, Jinyang He 写道:

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Hi, Thomas,

On 01/08/2021 01:26 AM, Thomas Bogendoerfer wrote:

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--- a/arch/mips/kernel/relocate_kernel.S
+++ b/arch/mips/kernel/relocate_kernel.S

@@ -6,6 +6,7 @@

   #include <asm/asm.h>
   #include <asm/asmmacro.h>
+#include <asm/cpu.h>
   #include <asm/regdef.h>
   #include <asm/mipsregs.h>
   #include <asm/stackframe.h>

@@ -133,6 +134,33 @@ LEAF(kexec_smp_wait)
   #else
       sync
   #endif
+
+#ifdef CONFIG_CPU_LOONGSON64

Is there a reason why you can't use the already existing infrastructure
the way cavium-octeon is doing it ? If you can't please explain why
so we can find a way to extend it. But having some sort of poking
loongson registers in generic MIPS code is a non starter.

Thomas.

Unlike the cavium-octeon platform, the Loongson64 platform needs some
changes. Before the kernel starts, (before entering the kernel_entry),
each CPU has its own state (the SMP system). For Loongson64, only the
boot CPU will enter the kernel_entry, and other CPUs will query their
mailbox value in a loop. This is what the BIOS does for the CPU. Here
is different from cavium-octeon. All CPUs will enter the kernel_entry
on cavium-octeon platform. Then the kernel_entry_setup, the co-CPUs
will enter the query loop. I saw the kernel_entry_setup of other
platforms, such as ip27, malta, and generic. They are not like
cavium-octeon and the co-CPUs entering the loop may be earlier than
entering kernel_entry. So I have reason to guess that most SMP system
platform CPUs are similar to Loongson64.

Hi Jingyang,

As I commented before you may reuse play_dead logic in Loongson's smp.c.

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relocate_kernel.S is like BIOS doing s omething for the CPU. It allows
the boot CPU to start from the new kernel_entry and makes the co-CPUs
enter a loop. The already existing infrastructure may be more suitable
for non-smp platforms. Although we can do something with
plat_smp_ops.kexec_nonboot_cpu, more new problems will arise in that
case. The kexec process actually runs on a copy of relocate_kernel.S,
which will bring a lot of problems...

It won't be a problem as you can keep all data on-stack without external
reference.

Thanks.

As I said before, only the control page is safe during kexec, so we
cannot reuse smp.c. If BIOS provides play_dead(), that is also a safe
region, but currently there is no runtime service from BIOS.

Huacai

- Jiaxun

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Above all just my personal thoughts.

Thanks,
Jinyang