cpufreq/amd-pstate: Fix amd_pstate mode switch on shared memory systems

While switching the driver mode between active and passive, Collaborative
Processor Performance Control (CPPC) is disabled in
amd_pstate_unregister_driver(). But, it is not enabled back while registering
the new driver (passive or active). This leads to the new driver mode not
working correctly, so enable it back in amd_pstate_register_driver().

Fixes: 3ca7bc8 ("cpufreq: amd-pstate: Add guided mode control support via sysfs")
Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20241004122303.94283-1-Dhananjay.Ugwekar@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

drivers/cpufreq/amd-pstate.c

@@ -1201,11 +1201,21 @@ static int amd_pstate_register_driver(int mode)
 		return -EINVAL;
 
 	cppc_state = mode;
+
+	ret = amd_pstate_enable(true);
+	if (ret) {
+		pr_err("failed to enable cppc during amd-pstate driver registration, return %d\n",
+		       ret);
+		amd_pstate_driver_cleanup();
+		return ret;
+	}
+
 	ret = cpufreq_register_driver(current_pstate_driver);
 	if (ret) {
 		amd_pstate_driver_cleanup();
 		return ret;
 	}
+
 	return 0;
 }