[Skiboot] [PATCH] Bail out when booting in big core mode

[Vaidyanathan Srinivasan]

* Joel Stanley <joel at jms.id.au> [2020-04-29 12:48:06]:

> This is not supported and will result in a misbehaving system later in
> boot.
> 
> We wait until the console is up so the developer can see what happened.
> 
> Signed-off-by: Joel Stanley <joel at jms.id.au>
> ---
> I see that there are some patches on the list to support this mode. If
> they don't go in soon, I ask that this change be added (and backported)
> to help developers who accidentally boot in big core mode.
> 
>  core/cpu.c          | 9 +++++++++
>  core/init.c         | 3 +++
>  include/cpu.h       | 3 +++
>  include/processor.h | 2 ++
>  4 files changed, 17 insertions(+)
> 
> diff --git a/core/cpu.c b/core/cpu.c
> index 37d9f41a8b79..f0c7e881e0f0 100644
> --- a/core/cpu.c
> +++ b/core/cpu.c
> @@ -935,6 +935,15 @@ static void init_cpu_thread(struct cpu_thread *t,
>  	assert(pir == container_of(t, struct cpu_stack, cpu) - cpu_stacks);
>  }
>  
> +void cpu_check_bigcore(void)
> +{
> +	unsigned int pvr = mfspr(SPR_PVR);
> +	if (PVR_TYPE(pvr) == PVR_TYPE_P9 && !(PVR_CHIP_TYPE(pvr) & 0x1)) {
> +		prerror("CPU: Detected unsupported POWER9 in big core mode.\n");
> +		abort();
> +	}
> +}
> +
>  static void enable_attn(void)
>  {
>  	unsigned long hid0;
> diff --git a/core/init.c b/core/init.c
> index 39cfd3fbe1b1..73a6756ebdb3 100644
> --- a/core/init.c
> +++ b/core/init.c
> @@ -1284,6 +1284,9 @@ void __noreturn __nomcount main_cpu_entry(const void *fdt)
>  	/* Install the OPAL Console handlers */
>  	init_opal_console();
>  
> +	/* Now that the console is up, bail out if we do not support the machine */
> +	cpu_check_bigcore();
> +

Hi Joel,

Without the big core enablement patch we hit asset() in
dt_add_cpufeatures() much earlier than this place.

I like the idea of atleast detecting the platform and then printing on
console and then abort().

But I do not know on which platform or combination of setting you
actually get to this point.  Share the PVR you ended up with.

We will actually need to check in Core-Thread-State register bit 63 to
confirm fused-core mode.

Let me split out the fused-core detection logic from the patch series
and add this clean way of aborting with message.  That will solve
cases where we unexpectedly boot in incorrect modes. This is a good
idea.

--Vaidy