cpufreq/amd-pstate: Remove warning for X86_FEATURE_CPPC on certain Zen models

commit bff7d13c190a ("cpufreq: amd-pstate: add debug message while
CPPC is supported and disabled by SBIOS") issues a warning on plaforms
where the X86_FEATURE_CPPC is expected to be enabled, but is not due
to it being disabled in the BIOS.

This feature bit corresponds to CPUID 0x80000008.ebx[27] which is a
reserved bit on the Zen1 processors and a reserved bit on Zen2 based
models 0x70-0x7F, and is expected to be cleared on these
platforms. Thus printing the warning message for these models when
X86_FEATURE_CPPC is unavailable is incorrect. Fix this.

Modify some of the comments, and use switch-case for model range
checking for improved readability while at it.

Fixes: bff7d13c190a ("cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS")
Cc: Xiaojian Du <xiaojian.du@amd.com>
Reported-by: David Wang <00107082@163.com>
Closes: https://lore.kernel.org/lkml/20240730140111.4491-1-00107082@163.com/
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Acked-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 89bda7a2bb8d131f981df2d39447a88854152ae2..259a917da75f352e04d66ab03bf05d8d9c1ca959 100644 (file)
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1834,20 +1834,34 @@ static bool amd_cppc_supported(void)
        }
 
        /*
-        * If the CPPC feature is disabled in the BIOS for processors that support MSR-based CPPC,
-        * the AMD Pstate driver may not function correctly.
-        * Check the CPPC flag and display a warning message if the platform supports CPPC.
-        * Note: below checking code will not abort the driver registeration process because of
-        * the code is added for debugging purposes.
+        * If the CPPC feature is disabled in the BIOS for processors
+        * that support MSR-based CPPC, the AMD Pstate driver may not
+        * function correctly.
+        *
+        * For such processors, check the CPPC flag and display a
+        * warning message if the platform supports CPPC.
+        *
+        * Note: The code check below will not abort the driver
+        * registration process because of the code is added for
+        * debugging purposes. Besides, it may still be possible for
+        * the driver to work using the shared-memory mechanism.
         */
        if (!cpu_feature_enabled(X86_FEATURE_CPPC)) {
-               if (cpu_feature_enabled(X86_FEATURE_ZEN1) || cpu_feature_enabled(X86_FEATURE_ZEN2)) {
-                       if (c->x86_model > 0x60 && c->x86_model < 0xaf)
+               if (cpu_feature_enabled(X86_FEATURE_ZEN2)) {
+                       switch (c->x86_model) {
+                       case 0x60 ... 0x6F:
+                       case 0x80 ... 0xAF:
                                warn = true;
-               } else if (cpu_feature_enabled(X86_FEATURE_ZEN3) || cpu_feature_enabled(X86_FEATURE_ZEN4)) {
-                       if ((c->x86_model > 0x10 && c->x86_model < 0x1F) ||
-                                       (c->x86_model > 0x40 && c->x86_model < 0xaf))
+                               break;
+                       }
+               } else if (cpu_feature_enabled(X86_FEATURE_ZEN3) ||
+                          cpu_feature_enabled(X86_FEATURE_ZEN4)) {
+                       switch (c->x86_model) {
+                       case 0x10 ... 0x1F:
+                       case 0x40 ... 0xAF:
                                warn = true;
+                               break;
+                       }
                } else if (cpu_feature_enabled(X86_FEATURE_ZEN5)) {
                        warn = true;
                }