imx: mx7: psci: improve cpu hotplug flow

This patch improves cpu hotplug, previous cpu_off
implementation is NOT safe, a CPU can NOT power down
itself in runtime, it will cause system bus hang due
to pending transaction. So need to use other online
CPU to kill it when it is ready for killed.

Here use SRC parameter register and a magic number
of ~0 as handshake for killing a offline CPU,
when the online CPU checks the psci_affinity_info,
it will help kill the offline CPU according to
the magic number stored in SRC parameter register.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>

arch/arm/mach-imx/mx7/psci-mx7.c

@@ -44,6 +44,14 @@
 #error "invalid value for CONFIG_ARMV7_PSCI_NR_CPUS"
 #endif
 
+#define imx_cpu_gpr_entry_offset(cpu) \
+	(SRC_BASE_ADDR + SRC_GPR1_MX7D + cpu * 8)
+#define imx_cpu_gpr_para_offset(cpu) \
+	(imx_cpu_gpr_entry_offset(cpu) + 4)
+
+#define IMX_CPU_SYNC_OFF	~0
+#define IMX_CPU_SYNC_ON		0
+
 u8 psci_state[IMX7D_PSCI_NR_CPUS] __secure_data = {
 	 PSCI_AFFINITY_LEVEL_ON,
 	 PSCI_AFFINITY_LEVEL_OFF};
@@ -116,7 +124,7 @@ __secure s32 psci_cpu_on(u32 __always_unused function_id, u32 mpidr, u32 ep,
 
 	psci_save(cpu, ep, context_id);
 
-	writel((u32)psci_cpu_entry, SRC_BASE_ADDR + cpu * 8 + SRC_GPR1_MX7D);
+	writel((u32)psci_cpu_entry, imx_cpu_gpr_entry_offset(cpu));
 
 	psci_set_state(cpu, PSCI_AFFINITY_LEVEL_ON_PENDING);
 
@@ -137,7 +145,11 @@ __secure s32 psci_cpu_off(void)
 
 	imx_enable_cpu_ca7(cpu, false);
 	imx_gpcv2_set_core_power(cpu, false);
-	writel(0, SRC_BASE_ADDR + cpu * 8 + SRC_GPR1_MX7D + 4);
+	/*
+	 * We use the cpu jumping argument register to sync with
+	 * psci_affinity_info() which is running on cpu0 to kill the cpu.
+	 */
+	writel(IMX_CPU_SYNC_OFF, imx_cpu_gpr_para_offset(cpu));
 
 	while (1)
 		wfi();
@@ -198,6 +210,13 @@ __secure s32 psci_affinity_info(u32 __always_unused function_id,
 	if (cpu >= IMX7D_PSCI_NR_CPUS)
 		return ARM_PSCI_RET_INVAL;
 
+	/* CPU is waiting for killed */
+	if (readl(imx_cpu_gpr_para_offset(cpu)) == IMX_CPU_SYNC_OFF) {
+		imx_enable_cpu_ca7(cpu, false);
+		imx_gpcv2_set_core_power(cpu, false);
+		writel(IMX_CPU_SYNC_ON, imx_cpu_gpr_para_offset(cpu));
+	}
+
 	return psci_state[cpu];
 }