在 2021/1/8 下午6:07, Jinyang He 写道:
Hi, Thomas,
On 01/08/2021 01:26 AM, Thomas Bogendoerfer wrote:
--- 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.
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.
- Jiaxun
Above all just my personal thoughts.
Thanks,
Jinyang
