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

On 3/8/24 15:57, Rob Herring wrote:

On Fri, Mar 08, 2024 at 07:23:35AM -0500, Stefan Berger wrote:

quoted

On 3/7/24 16:52, Rob Herring wrote:

quoted

On Thu, Mar 07, 2024 at 09:41:31PM +1100, Michael Ellerman wrote:

quoted

Stefan Berger [off-list ref] writes:

quoted

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(-)

quoted

quoted

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.