[Skiboot] [PATCH 1/2] debug_descriptor: Claim reserved field for host kernel log buffer

[Joel Stanley]

On 25 May 2018 at 15:24, Vasant Hegde <hegdevasant at linux.vnet.ibm.com> wrote:
> On 05/24/2018 07:07 AM, Joel Stanley wrote:
>>
>> Signed-off-by: Joel Stanley <joel at jms.id.au>
>> ---
>> We could bump the version instead, but I don't think there's any call
>> for that.
>>
>> Another option would be to re-use some of the memcons fields that are
>> currently only used by FSP.
>>
>> A third option would be to use this field to link to yet another debug
>> structure to allow for future flexibility.
>> ---
>>   include/skiboot.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/skiboot.h b/include/skiboot.h
>> index b4bdf37795dd..7f3740965412 100644
>> --- a/include/skiboot.h
>> +++ b/include/skiboot.h
>> @@ -75,7 +75,7 @@ struct debug_descriptor {
>>                                          * low 4 bits driver (e.g. uart).
>> */
>>         u8      state_flags; /* various state flags - OPAL_BOOT_COMPLETE
>> etc */
>>         u16     reserved2;
>> -       u32     reserved[2];
>> +       u64     log_buf_phys;           /* Pointer to kernel log buffer */
>
>
> May be increment DEBUG_DESC_VERSION as well? So that user can identify
> whether this field
> is supported or not?

I considered this. Users running skiboot before this patch will see
zeros for the reserved[2] field. Users running skiboot after this
patch will either see zeroes, or see the field populated with the
memory address. Given that there's no change in behaviour, I don't
think there's any value in bumping the field.

That said, there's no reason bumping the value will hurt, if someone
thinks we need to. I'll leave it as-is for now.

Cheers,

Joel