@@ -13,6 +13,8 @@
#include <linux/io.h>
#include <linux/bitops.h>
#include <linux/of_address.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
#include <asm/cacheflush.h>
#include <asm/hardware/cache-b15-rac.h>
@@ -44,6 +46,7 @@ extern void v7_flush_icache_all(void);
static void __iomem *b15_rac_base;
static DEFINE_SPINLOCK(rac_lock);
+static u32 rac_config0_reg;
/* Initialization flag to avoid checking for b15_rac_base, and to prevent
* multi-platform kernels from crashing here as well.
@@ -142,6 +145,94 @@ static void b15_rac_enable(void)
__b15_rac_enable(enable);
}
+#ifdef CONFIG_HOTPLUG_CPU
+static void b15_rac_hotplug_start(void)
+{
+ /* Indicate that we are starting a hotplug procedure */
+ clear_bit(RAC_ENABLED, &b15_rac_flags);
+
+ /* Disable the readahead cache and save its value to a global */
+ rac_config0_reg = b15_rac_disable_and_flush();
+}
+
+static void b15_rac_hotplug_end(void)
+{
+ /* And enable it */
+ __b15_rac_enable(rac_config0_reg);
+ set_bit(RAC_ENABLED, &b15_rac_flags);
+}
+
+/* The CPU hotplug case is the most interesting one, we basically need to make
+ * sure that the RAC is disabled for the entire system prior to having a CPU
+ * die, in particular prior to this dying CPU having exited the coherency
+ * domain.
+ *
+ * Once this CPU is marked dead, we can safely re-enable the RAC for the
+ * remaining CPUs in the system which are still online.
+ *
+ * Offlining a CPU is the problematic case, onlining a CPU is not much of an
+ * issue since the CPU and its cache-level hierarchy will start filling with
+ * the RAC disabled, so L1 and L2 only.
+ *
+ * In this function, we should NOT have to verify any unsafe setting/condition
+ * b15_rac_base:
+ *
+ * It is protected by the RAC_ENABLED flag which is cleared by default, and
+ * being cleared when initial procedure is done. b15_rac_base had been set at
+ * that time.
+ *
+ * RAC_ENABLED:
+ * There is a small timing windows, in b15_rac_init(), between
+ * register_cpu_notifier(&b15_rac_cpu_nb);
+ * ...
+ * set RAC_ENABLED
+ * However, there is no hotplug activity based on the Linux booting procedure.
+ *
+ * Regarding the notification actions, we will receive CPU_DOWN_PREPARE,
+ * CPU_DOWN_FAILED, CPU_DYING, CPU_DEAD, and CPU_POST_DEAD notification (see
+ * _cpu_down() for detail).
+ *
+ * Since we have to disable RAC for all cores, we keep RAC on as long as as
+ * possible (disable it as late as possible) to gain the cache benefit.
+ *
+ * Thus, CPU_DYING/CPU_DEAD pair are chosen.
+ *
+ * We are choosing not do disable the RAC on a per-CPU basis, here, if we did
+ * we would want to consider disabling it as early as possible to benefit the
+ * other active CPUs.
+ */
+static int b15_rac_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ action &= ~CPU_TASKS_FROZEN;
+
+ if (action != CPU_DYING && action != CPU_DOWN_FAILED &&
+ action != CPU_DEAD)
+ return NOTIFY_OK;
+
+ spin_lock(&rac_lock);
+ switch (action) {
+ /* called on the dying CPU, exactly what we want */
+ case CPU_DYING:
+ b15_rac_hotplug_start();
+ break;
+
+ /* called on a non-dying CPU, what we want too */
+ case CPU_DOWN_FAILED:
+ case CPU_DEAD:
+ b15_rac_hotplug_end();
+ break;
+ }
+ spin_unlock(&rac_lock);
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block b15_rac_cpu_nb = {
+ .notifier_call = b15_rac_cpu_notify,
+};
+#endif /* CONFIG_HOTPLUG_CPU */
+
static int __init b15_rac_init(void)
{
struct device_node *dn;
@@ -161,6 +252,15 @@ static int __init b15_rac_init(void)
goto out;
}
+#ifdef CONFIG_HOTPLUG_CPU
+ ret = register_cpu_notifier(&b15_rac_cpu_nb);
+ if (ret) {
+ pr_err("failed to register notifier block\n");
+ iounmap(b15_rac_base);
+ goto out;
+ }
+#endif
+
spin_lock(&rac_lock);
reg = __raw_readl(b15_rac_base + RAC_CONFIG0_REG);
for_each_possible_cpu(cpu)