x86: Add msr command

It is useful to obtain the results of MSR queries as well as to update
MSR registers, so add a command these tasks.

Signed-off-by: Simon Glass <[email protected]>

2 files changed, 62 insertions, 0 deletions

diff --git a/doc/usage/cmd/msr.rst b/doc/usage/cmd/msr.rst
new file mode 100644
index 00000000000..04ee52cc1c7
--- /dev/null
+++ b/doc/usage/cmd/msr.rst
@@ -0,0 +1,61 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+.. index::
+   single: msr (command)
+
+msr command
+===========
+
+Synopsis
+--------
+
+::
+
+    msr read <op>
+    msr write <op> <hi> <lo>
+
+Description
+-----------
+
+The msr command reads and writes machine-status registers (MSRs) on x86 CPUs.
+The information is a 64-bit value split into two parts, <hi> for the top 32
+bits and <lo> for the bottom 32 bits.
+
+The operation <op> selects what information is read or written.
+
+msr read
+~~~~~~~~
+
+This reads an MSR and displays the value obtained.
+
+msr write
+~~~~~~~~~
+
+This writes a value to an MSR.
+
+Configuration
+-------------
+
+The msr command is only available on x86.
+
+Return value
+------------
+
+The return value $? is 0 (true).
+
+Example
+-------
+
+This shows reading msr 0x194 which is MSR_FLEX_RATIO on Intel CPUs::
+
+    => msr read 194
+    00000000 00011200   # Bits 16 (flex ratio enable) and 20 (lock) are set
+
+This shows adjusting the energy-performance bias on an Intel CPU::
+
+    => msr read 1b0
+    00000000 00000006     # 6 means 'normal'
+
+    => msr write 1b0 0 f  # change to power-save
+    => msr read 1b0
+    00000000 0000000f
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index d2b187b0118..b84d8ee909f 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -87,6 +87,7 @@ Shell commands
    cmd/mbr
    cmd/md
    cmd/mmc
+   cmd/msr
    cmd/mtest
    cmd/mtrr
    cmd/panic