arm_mpam: Allow the maximum partid to be overridden from the command line

MPAMs bandwidth monitors are only available via resctrl if there are
enough monitors for each combination of partid and pmg to have one.

As it is unlikely anyone built that many monitors, allow the
maximum partid the system will use to be set from the kernel
command-line.

With this, it should be possible to bandwidth monitors to be
enabled by reducing the number of partid in use.

Signed-off-by: James Morse <james.morse@arm.com>

drivers/platform/mpam/mpam_devices.c

@@ -60,6 +60,8 @@ static DEFINE_MUTEX(mpam_cpuhp_state_lock);
 u16 mpam_partid_max;
 u8 mpam_pmg_max;
 static bool partid_max_init, partid_max_published;
+static u16 mpam_cmdline_partid_max;
+static bool mpam_cmdline_partid_max_overridden;
 static DEFINE_SPINLOCK(partid_max_lock);
 
 /*
@@ -200,6 +202,9 @@ int mpam_register_requestor(u16 partid_max, u8 pmg_max)
 		if ((partid_max < mpam_partid_max) || (pmg_max < mpam_pmg_max))
 			err = -EBUSY;
 	}
+
+	if (mpam_cmdline_partid_max_overridden)
+		mpam_partid_max = min(mpam_cmdline_partid_max, mpam_partid_max);
 	spin_unlock(&partid_max_lock);
 
 	return err;
@@ -2419,3 +2424,17 @@ static int __init mpam_msc_driver_init(void)
 }
 /* Must occur after arm64_mpam_register_cpus() from arch_initcall() */
 subsys_initcall(mpam_msc_driver_init);
+
+static int __init mpam_parse_partid_max(char *arg)
+{
+	int ret;
+
+	spin_lock(&partid_max_lock);
+	ret = kstrtou16(arg, 10, &mpam_cmdline_partid_max);
+	spin_unlock(&partid_max_lock);
+	if (!ret)
+		mpam_cmdline_partid_max_overridden = true;
+
+	return 0;
+}
+early_param("mpam.partid_max", mpam_parse_partid_max);