[PATCH v2 2/2] docs: powerpc: Add ELF note documentation

From: Maxiwell S. Garcia
Date: Thu Aug 29 2019 - 11:51:23 EST

The ELF note documentation describes the types and descriptors to be
used with the PowerPC namespace.

Signed-off-by: Maxiwell S. Garcia <maxiwell@xxxxxxxxxxxxx>
Signed-off-by: Claudio Carvalho <cclaudio@xxxxxxxxxxxxx>
Documentation/powerpc/elfnote.rst | 42 +++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
create mode 100644 Documentation/powerpc/elfnote.rst

diff --git a/Documentation/powerpc/elfnote.rst b/Documentation/powerpc/elfnote.rst
new file mode 100644
index 000000000000..2a5c4beeb809
--- /dev/null
+++ b/Documentation/powerpc/elfnote.rst
@@ -0,0 +1,42 @@
+ELF Note PowerPC Namespace
+The PowerPC namespace in an ELF Note of the kernel binary is used to store
+capabilities and information which can be used by a bootloader or userland.
+Types and Descriptors
+The types to be used with the "PowerPC" namesapce are defined in the
+Define the capabilities supported/required by the kernel. This type uses a
+bitmap as "descriptor" field. Each bit is described below:
+- Ultravisor-capable bit (PowerNV only).
+ #define PPCCAP_ULTRAVISOR_BIT (1 << 0)
+ Indicate that the powerpc kernel binary knows how to run in an
+ ultravisor-enabled system.
+ In an ultravisor-enabled system, some machine resources are now controlled
+ by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
+ being run on a machine with ultravisor, the kernel will probably crash
+ trying to access ultravisor resources. For instance, it may crash in early
+ boot trying to set the partition table entry 0.
+ In an ultravisor-enabled system, a bootloader could warn the user or prevent
+ the kernel from being run if the PowerPC ultravisor capability doesn't exist
+ or the Ultravisor-capable bit is not set.