Re: [PATCH 1/2] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

Stefan Berger
2024-03-08T21:26:31Z

On 3/8/24 15:57, Rob Herring wrote:
> On Fri, Mar 08, 2024 at 07:23:35AM -0500, Stefan Berger wrote:
>>
>>
>> On 3/7/24 16:52, Rob Herring wrote:
>>> On Thu, Mar 07, 2024 at 09:41:31PM +1100, Michael Ellerman wrote:
>>>> Stefan Berger <stefanb@linux.ibm.com> writes:
>>>>> linux,sml-base holds the address of a buffer with the TPM log. This
>>>>> buffer may become invalid after a kexec and therefore embed the whole TPM
>>>>> log in linux,sml-log. This helps to protect the log since it is properly
>>>>> carried across a kexec with both of the kexec syscalls.
>>>>>
>>>>> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
>>>>> ---
>>>>> arch/powerpc/kernel/prom_init.c | 8 ++------
>>>>> 1 file changed, 2 insertions(+), 6 deletions(-)
>>>>>
>>
>>>
>>>
>>>> Also adding the new linux,sml-log property should be accompanied by a
>>>> change to the device tree binding.
>>>>
>>>> The syntax is not very obvious to me, but possibly something like?
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml b/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>>>> index 50a3fd31241c..cd75037948bc 100644
>>>> --- a/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>>>> +++ b/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>>>> @@ -74,8 +74,6 @@ required:
>>>> - ibm,my-dma-window
>>>> - ibm,my-drc-index
>>>> - ibm,loc-code
>>>> - - linux,sml-base
>>>> - - linux,sml-size
>>>
>>> Dropping required properties is an ABI break. If you drop them, an older
>>> OS version won't work.
>>
>> 1) On PowerVM and KVM on Power these two properties were added in the Linux
>> code. I replaced the creation of these properties with creation of
>> linux,sml-log (1/2 in this series). I also replaced the handling of
>> these two (2/2 in this series) for these two platforms but leaving it for
>> powernv systems where the firmware creates these.
>
> Okay, I guess your case is not a ABI break if the kernel is populating
> it and the same kernel consumes it.
>
> You failed to answer my question on using /reserved-memory. Again, why

I am not familiar with /reserved-memory and whether it is supported on
the targeted platforms.