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 <sjg@chromium.org>

cmd/x86/Makefile

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0+
 
 obj-$(CONFIG_CMD_CBSYSINFO) += cbsysinfo.o
-obj-y += cpuid.o mtrr.o
+obj-y += cpuid.o msr.o mtrr.o
 obj-$(CONFIG_CMD_EXCEPTION) += exception.o
 obj-$(CONFIG_USE_HOB) += hob.o
 obj-$(CONFIG_HAVE_FSP) += fsp.o

cmd/x86/msr.c

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * The 'cpuid' command provides access to the CPU's cpuid information
+ *
+ * Copyright 2024 Google, LLC
+ * Written by Simon Glass <sjg@chromium.org>
+ */
+
+#include <command.h>
+#include <vsprintf.h>
+#include <asm/msr.h>
+
+static int do_read(struct cmd_tbl *cmdtp, int flag, int argc,
+		   char *const argv[])
+{
+	struct msr_t msr;
+	ulong op;
+
+	if (argc < 2)
+		return CMD_RET_USAGE;
+
+	op = hextoul(argv[1], NULL);
+	msr = msr_read(op);
+	printf("%08x %08x\n", msr.hi, msr.lo);
+
+	return 0;
+}
+
+static int do_write(struct cmd_tbl *cmdtp, int flag, int argc,
+		    char *const argv[])
+{
+	struct msr_t msr;
+	ulong op;
+
+	if (argc < 4)
+		return CMD_RET_USAGE;
+
+	op = hextoul(argv[1], NULL);
+	msr.hi = hextoul(argv[2], NULL);
+	msr.lo = hextoul(argv[3], NULL);
+	msr_write(op, msr);
+
+	return 0;
+}
+
+U_BOOT_LONGHELP(msr,
+	"read <op>         - read a machine-status register (MSR) as <hi 32-bits> <lo 32-bits>\n"
+	"write <op< <hi> <lo>  - write an MSR");
+
+U_BOOT_CMD_WITH_SUBCMDS(msr, "Machine Status Registers", msr_help_text,
+	U_BOOT_CMD_MKENT(read, CONFIG_SYS_MAXARGS, 1, do_read, "", ""),
+	U_BOOT_CMD_MKENT(write, CONFIG_SYS_MAXARGS, 1, do_write, "", ""));

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

doc/usage/index.rst

@@ -87,6 +87,7 @@ Shell commands
    cmd/mbr
    cmd/md
    cmd/mmc
+   cmd/msr
    cmd/mtest
    cmd/mtrr
    cmd/panic

test/cmd/Makefile

@@ -12,7 +12,7 @@ ifdef CONFIG_CONSOLE_RECORD
 obj-$(CONFIG_CMD_PAUSE) += test_pause.o
 endif
 obj-y += exit.o mem.o
-obj-$(CONFIG_X86) += cpuid.o
+obj-$(CONFIG_X86) += cpuid.o msr.o
 obj-$(CONFIG_CMD_ADDRMAP) += addrmap.o
 obj-$(CONFIG_CMD_BDI) += bdinfo.o
 obj-$(CONFIG_CMD_FDT) += fdt.o

test/cmd/msr.c

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Tests for msr command
+ *
+ * Copyright 2024 Google LLC
+ * Written by Simon Glass <sjg@chromium.org>
+ */
+
+#include <test/cmd.h>
+#include <test/ut.h>
+
+static int cmd_test_msr(struct unit_test_state *uts)
+{
+	ut_assertok(run_commandf("msr read 200"));
+	ut_assert_nextline("00000000 ffe00006");
+	ut_assert_console_end();
+
+	/* change the first variable msr and see it reflected in the mtrr cmd */
+	ut_assertok(run_commandf("mtrr"));
+	ut_assert_nextline("CPU 65537:");
+	ut_assert_nextlinen("Reg");
+	ut_assert_nextlinen("0   Y     Back         00000000ffe00000");
+	ut_assertok(console_record_reset_enable());
+
+	/* change the type from 6 to 5 */
+	ut_assertok(run_commandf("msr write 200 0 ffe00005"));
+	ut_assert_console_end();
+
+	/* Now it shows 'Protect' */
+	ut_assertok(run_commandf("mtrr"));
+	ut_assert_nextline("CPU 65537:");
+	ut_assert_nextlinen("Reg");
+	ut_assert_nextlinen("0   Y     Protect      00000000ffe00000");
+	ut_assertok(console_record_reset_enable());
+
+	return 0;
+}
+CMD_TEST(cmd_test_msr, UTF_CONSOLE);