[PATCH 1/2] x86/fred: enable FRED by default

[H. Peter Anvin]

When FRED was added to the mainline kernel, it was set up as an
explicit opt-in due to the risk of regressions before hardware was
available publicly.

Now, Panther Lake (Core Ultra 300 series) has been released, and
benchmarking by Phoronix has shown that it provides a significant
performance benefit on most workloads:

    https://www.phoronix.com/review/intel-fred-panther-lake

Accordingly, enable FRED by default if the CPU supports it. FRED can
of course still be disabled via the fred=off command line option.

Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++--
 arch/x86/kernel/cpu/common.c                    | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 03a550630644..bfa8a20ccc37 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1750,8 +1750,8 @@ Kernel parameters
 	fred=		[X86-64]
 			Enable/disable Flexible Return and Event Delivery.
 			Format: { on | off }
-			on: enable FRED when it's present.
-			off: disable FRED, the default setting.
+			on: enable FRED when it's present, the default setting.
+			off: disable FRED.
 
 	ftrace=[tracer]
 			[FTRACE] will set and start the specified tracer
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a8ff4376c286..e22a49869380 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1746,7 +1746,7 @@ static void __init cpu_parse_early_param(void)
 
 	/* Minimize the gap between FRED is available and available but disabled. */
 	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
-	if (arglen != 2 || strncmp(arg, "on", 2))
+	if (arglen > 0 && (arglen != 2 || strncmp(arg, "on", 2)))
 		setup_clear_cpu_cap(X86_FEATURE_FRED);
 
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
-- 
2.53.0