MIPS: CPS: Improve mips_cps_first_online_in_cluster()

The initial implementation of this function goes through all the CPUs
in a cluster to determine if the current CPU is the only one
running. This process occurs every time the function is called.

However, during boot, we already perform this task, so let's take
advantage of this opportunity to create and fill a CPU bitmask that
can be easily and efficiently used later.

This patch modifies the function to allow providing the first
available online CPU when one already exists, which is necessary for
delay CPU calibration optimization.

Reviewed-by: Jiaxun Yang <[e-mail]>
Signed-off-by: Gregory CLEMENT <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/include/asm/mips-cps.h

···
 
 /**
  * mips_cps_first_online_in_cluster() - Detect if CPU is first online in cluster
+ * @first_cpu: The first other online CPU in cluster, or nr_cpu_ids if
+ * the function returns true.
  *
  * Determine whether the local CPU is the first to be brought online in its
  * cluster - that is, whether there are any other online CPUs in the local
···
  *
  * Returns true if this CPU is first online, else false.
  */
-extern unsigned int mips_cps_first_online_in_cluster(void);
+extern unsigned int mips_cps_first_online_in_cluster(int *first_cpu);
 
 #endif /* __MIPS_ASM_MIPS_CPS_H__ */

arch/mips/include/asm/smp-cps.h

···
 
 struct cluster_boot_config {
 	unsigned long *core_power;
+	struct cpumask cpumask;
 	struct core_boot_config *core_config;
 };
 

arch/mips/kernel/mips-cm.c

···
 #include <linux/spinlock.h>
 
 #include <asm/mips-cps.h>
+#include <asm/smp-cps.h>
 #include <asm/mipsregs.h>
 
 void __iomem *mips_gcr_base;
···
 	write_gcr_error_cause(cm_error);
 }
 
-unsigned int mips_cps_first_online_in_cluster(void)
+unsigned int mips_cps_first_online_in_cluster(int *first_cpu)
 {
-	unsigned int local_cl;
-	int i;
-
-	local_cl = cpu_cluster(&current_cpu_data);
+	unsigned int local_cl = cpu_cluster(&current_cpu_data);
+	struct cpumask *local_cl_mask;
 
 	/*
-	 * We rely upon knowledge that CPUs are numbered sequentially by
-	 * cluster - ie. CPUs 0..X will be in cluster 0, CPUs X+1..Y in cluster
-	 * 1, CPUs Y+1..Z in cluster 2 etc. This means that CPUs in the same
-	 * cluster will immediately precede or follow one another.
-	 *
-	 * First we scan backwards, until we find an online CPU in the cluster
-	 * or we move on to another cluster.
+	 * mips_cps_cluster_bootcfg is allocated in cps_prepare_cpus. If it is
+	 * not yet done, then we are so early that only one CPU is running, so
+	 * it is the first online CPU in the cluster.
 	 */
-	for (i = smp_processor_id() - 1; i >= 0; i--) {
-		if (cpu_cluster(&cpu_data[i]) != local_cl)
-			break;
-		if (!cpu_online(i))
-			continue;
-		return false;
-	}
+	if  (IS_ENABLED(CONFIG_MIPS_CPS) && mips_cps_cluster_bootcfg)
+		local_cl_mask = &mips_cps_cluster_bootcfg[local_cl].cpumask;
+	else
+		return true;
 
-	/* Then do the same for higher numbered CPUs */
-	for (i = smp_processor_id() + 1; i < nr_cpu_ids; i++) {
-		if (cpu_cluster(&cpu_data[i]) != local_cl)
-			break;
-		if (!cpu_online(i))
-			continue;
-		return false;
-	}
-
-	/* We found no online CPUs in the local cluster */
-	return true;
+	*first_cpu = cpumask_any_and_but(local_cl_mask,
+					 cpu_online_mask,
+					 smp_processor_id());
+	return (*first_cpu >= nr_cpu_ids);
 }

arch/mips/kernel/smp-cps.c

···
 
 static void __init cps_prepare_cpus(unsigned int max_cpus)
 {
-	unsigned int nclusters, ncores, core_vpes, c, cl, cca;
+	unsigned int nclusters, ncores, core_vpes, nvpe = 0, c, cl, cca;
 	bool cca_unsuitable, cores_limited;
 	struct cluster_boot_config *cluster_bootcfg;
 	struct core_boot_config *core_bootcfg;
···
 
 		/* Allocate VPE boot configuration structs */
 		for (c = 0; c < ncores; c++) {
+			int v;
 			core_vpes = core_vpe_count(cl, c);
 			core_bootcfg[c].vpe_config = kcalloc(core_vpes,
 					sizeof(*core_bootcfg[c].vpe_config),
 					GFP_KERNEL);
+			for (v = 0; v < core_vpes; v++)
+				cpumask_set_cpu(nvpe++, &mips_cps_cluster_bootcfg[cl].cpumask);
 			if (!core_bootcfg[c].vpe_config)
 				goto err_out;
 		}