[PATCH V3] MIPS: Loongson64: Add kexec/kdump support

[Huacai Chen]

Hi, Jiaxun,

On Fri, Jan 8, 2021 at 6:15 PM Jiaxun Yang <jiaxun.yang at flygoat.com> wrote:
>
> 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.
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
>
> >
> > Above all just my personal thoughts.
> >
> > Thanks,
> > Jinyang
> >
>