[PATCH] powerpc/pasemi/nemo: Fix low memory values for boot.

[PATCH] powerpc/pasemi/nemo: Fix low memory values for boot.

[Darren Stevens]

Commit 5c0484e25ec0 ('powerpc: Endian safe trampoline') added a
macro 'FIXUP_ENDIAN' to head_64.S. The CFE on Nemo has a bug 
that shows up when this is included, the system hangs right after
printing the initial memory map, before the CPU's are started.

Clearing the long long at addr 8 has been shown to fix this, so
add an initalisation to head_64.S so the system will boot.

Signed-off-by: Darren Stevens <darren@stevens-zone.net>

---

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 1dc5eae..032b317 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -79,6 +79,13 @@ _GLOBAL(__start)
    /* NOP this out unconditionally */
 BEGIN_FTR_SECTION
    FIXUP_ENDIAN
+#ifdef CONFIG_PPC_PASEMI_NEMO
+   /*
+    * Zero address 8 so Nemo will boot
+    */
+   li  r0,0
+   std 0,8(0)
+#endif
    b   __start_initialization_multiplatform
 END_FTR_SECTION(0, 1)
 

Re: [PATCH] powerpc/pasemi/nemo: Fix low memory values for boot.

[Segher Boessenkool]

On Fri, Jan 20, 2017 at 05:46:13PM +0000, Darren Stevens wrote:
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -79,6 +79,13 @@ _GLOBAL(__start)
>     /* NOP this out unconditionally */
>  BEGIN_FTR_SECTION
>     FIXUP_ENDIAN
> +#ifdef CONFIG_PPC_PASEMI_NEMO
> +   /*
> +    * Zero address 8 so Nemo will boot
> +    */
> +   li  r0,0
> +   std 0,8(0)
> +#endif

std r0,8(0)   for clarity?


Segher

Re: [PATCH] powerpc/pasemi/nemo: Fix low memory values for boot.

[Michael Ellerman]

Darren Stevens <darren@stevens-zone.net> writes:

> Commit 5c0484e25ec0 ('powerpc: Endian safe trampoline') added a
> macro 'FIXUP_ENDIAN' to head_64.S. The CFE on Nemo has a bug 
> that shows up when this is included, the system hangs right after
> printing the initial memory map, before the CPU's are started.
>
> Clearing the long long at addr 8 has been shown to fix this, so
> add an initalisation to head_64.S so the system will boot.

I'd really prefer it if someone could tell me why we need to clear it.
But I assume no one knows?

> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 1dc5eae..032b317 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -79,6 +79,13 @@ _GLOBAL(__start)
>     /* NOP this out unconditionally */
>  BEGIN_FTR_SECTION
>     FIXUP_ENDIAN
> +#ifdef CONFIG_PPC_PASEMI_NEMO
> +   /*
> +    * Zero address 8 so Nemo will boot
> +    */
> +   li  r0,0
> +   std 0,8(0)
> +#endif
>     b   __start_initialization_multiplatform
>  END_FTR_SECTION(0, 1)
 
I don't want to pollute this code with NEMO workarounds if we can avoid
it.

You said the hang happens after printing the initial memory map, I'm not
quite sure where you mean, but it sounds like that will be late enough
that we can do the clear in pasemi platform code?

cheers

Re: powerpc/pasemi/nemo: Fix low memory values for boot.

[Darren Stevens]

Hello Michael

On 23/01/2017, Michael Ellerman wrote:
>> Clearing the long long at addr 8 has been shown to fix this, so
>> add an initalisation to head_64.S so the system will boot.
>
> I'd really prefer it if someone could tell me why we need to clear it.
> But I assume no one knows?

The problem was found by Christian, and the fix comes courtesy of Olof
Johansson, I've not looked into it before.

> I don't want to pollute this code with NEMO workarounds if we can avoid
> it.

To be honest, so would I.

> You said the hang happens after printing the initial memory map, I'm not
> quite sure where you mean, but it sounds like that will be late enough
> that we can do the clear in pasemi platform code?

During prom_init. Where it says 'Memory layout at Init'

I took a long look today and traced the problem the 'prom_find_boot_cpu' and a
much better patch will follow.

Regards
Darren

Re: powerpc/pasemi/nemo: Fix low memory values for boot.

[Michael Ellerman]

Darren Stevens <darren@stevens-zone.net> writes:
> On 23/01/2017, Michael Ellerman wrote:
>>> Clearing the long long at addr 8 has been shown to fix this, so
>>> add an initalisation to head_64.S so the system will boot.
>>
>> I'd really prefer it if someone could tell me why we need to clear it.
>> But I assume no one knows?
...
>
> I took a long look today and traced the problem the 'prom_find_boot_cpu' and a
> much better patch will follow.

Awesome work, thanks.

cheers