ARM: vexpress/dcscb: add CPU use counts to the power up/down API implementation

It is possible for a CPU to be told to power up before it managed
to power itself down.  Solve this race with a usage count to deal
with this possibility as mandated by the MCPM API definition.

Signed-off-by: nicolas Pitre <nico@linaro.org>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>

1 files changed, 59 insertions, 15 deletions

diff --git a/arch/arm/mach-vexpress/dcscb.c b/arch/arm/mach-vexpress/dcscb.c
index 2ca4bbce530c..65dee7818082 100644
--- a/arch/arm/mach-vexpress/dcscb.c
+++ b/arch/arm/mach-vexpress/dcscb.c
@@ -44,6 +44,7 @@
 static arch_spinlock_t dcscb_lock = __ARCH_SPIN_LOCK_UNLOCKED;
 
 static void __iomem *dcscb_base;
+static int dcscb_use_count[4][2];
 
 static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
 {
@@ -60,14 +61,27 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
         local_irq_disable();
         arch_spin_lock(&dcscb_lock);
 
-        rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
-        if (rst_hold & (1 << 8)) {
-                /* remove cluster reset and add individual CPU's reset */
-                rst_hold &= ~(1 << 8);
-                rst_hold |= 0xf;
+        dcscb_use_count[cpu][cluster]++;
+        if (dcscb_use_count[cpu][cluster] == 1) {
+                rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
+                if (rst_hold & (1 << 8)) {
+                        /* remove cluster reset and add individual CPU's reset */
+                        rst_hold &= ~(1 << 8);
+                        rst_hold |= 0xf;
+                }
+                rst_hold &= ~(cpumask | (cpumask << 4));
+                writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+        } else if (dcscb_use_count[cpu][cluster] != 2) {
+                /*
+                 * The only possible values are:
+                 * 0 = CPU down
+                 * 1 = CPU (still) up
+                 * 2 = CPU requested to be up before it had a chance
+                 *     to actually make itself down.
+                 * Any other value is a bug.
+                 */
+                BUG();
         }
-        rst_hold &= ~(cpumask | (cpumask << 4));
-        writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
 
         arch_spin_unlock(&dcscb_lock);
         local_irq_enable();
@@ -77,7 +91,8 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
 
 static void dcscb_power_down(void)
 {
-        unsigned int mpidr, cpu, cluster, rst_hold, cpumask, last_man;
+        unsigned int mpidr, cpu, cluster, rst_hold, cpumask;
+        bool last_man = false, skip_wfi = false;
 
         mpidr = read_cpuid_mpidr();
         cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
@@ -88,13 +103,26 @@ static void dcscb_power_down(void)
         BUG_ON(cpu >= 4 || cluster >= 2);
 
         arch_spin_lock(&dcscb_lock);
-        rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
-        rst_hold |= cpumask;
-        if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf)
-                rst_hold |= (1 << 8);
-        writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+        dcscb_use_count[cpu][cluster]--;
+        if (dcscb_use_count[cpu][cluster] == 0) {
+                rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
+                rst_hold |= cpumask;
+                if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf) {
+                        rst_hold |= (1 << 8);
+                        last_man = true;
+                }
+                writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+        } else if (dcscb_use_count[cpu][cluster] == 1) {
+                /*
+                 * A power_up request went ahead of us.
+                 * Even if we do not want to shut this CPU down,
+                 * the caller expects a certain state as if the WFI
+                 * was aborted.  So let's continue with cache cleaning.
+                 */
+                skip_wfi = true;
+        } else
+                BUG();
         arch_spin_unlock(&dcscb_lock);
-        last_man = (rst_hold & (1 << 8));
 
         /*
          * Now let's clean our L1 cache and shut ourself down.
@@ -122,7 +150,8 @@ static void dcscb_power_down(void)
 
         /* Now we are prepared for power-down, do it: */
         dsb();
-        wfi();
+        if (!skip_wfi)
+                wfi();
 
         /* Not dead at this point?  Let our caller cope. */
 }
@@ -132,6 +161,19 @@ static const struct mcpm_platform_ops dcscb_power_ops = {
         .power_down     = dcscb_power_down,
 };
 
+static void __init dcscb_usage_count_init(void)
+{
+        unsigned int mpidr, cpu, cluster;
+
+        mpidr = read_cpuid_mpidr();
+        cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+        cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+
+        pr_debug("%s: cpu %u cluster %u\n", __func__, cpu, cluster);
+        BUG_ON(cpu >= 4 || cluster >= 2);
+        dcscb_use_count[cpu][cluster] = 1;
+}
+
 static int __init dcscb_init(void)
 {
         struct device_node *node;
@@ -144,6 +186,8 @@ static int __init dcscb_init(void)
         if (!dcscb_base)
                 return -EADDRNOTAVAIL;
 
+        dcscb_usage_count_init();
+
         ret = mcpm_platform_register(&dcscb_power_ops);
         if (ret) {
                 iounmap(dcscb_base);