Fix broken standby state implementation in PSCI
This patch fixes the broken support for entry into standby states
introduced under commit-id 'd118f9f864' (tf-issues#94). Upon exit from
the platform defined standby state instead of returning to the caller
of the SMC, execution would get stuck in the wfi instruction meant for
entering a power down state. This patch ensures that exit from a
standby state and entry into a power down state do not interfere with
each other.
Fixes ARM-software/tf-issues#154
Change-Id: I56e5df353368e44d6eefc94ffedefe21929f5cfe
diff --git a/include/bl31/services/psci.h b/include/bl31/services/psci.h
index 570fe5b..b6e272c 100644
--- a/include/bl31/services/psci.h
+++ b/include/bl31/services/psci.h
@@ -190,6 +190,7 @@
extern int psci_cpu_on(unsigned long,
unsigned long,
unsigned long);
+extern void __dead2 psci_power_down_wfi(void);
extern void psci_aff_on_finish_entry(void);
extern void psci_aff_suspend_finish_entry(void);
extern void psci_register_spd_pm_hook(const spd_pm_ops_t *);
diff --git a/services/std_svc/psci/psci_entry.S b/services/std_svc/psci/psci_entry.S
index 256c538..3d0181a 100644
--- a/services/std_svc/psci/psci_entry.S
+++ b/services/std_svc/psci/psci_entry.S
@@ -37,6 +37,7 @@
.globl psci_aff_suspend_finish_entry
.globl __psci_cpu_off
.globl __psci_cpu_suspend
+ .globl psci_power_down_wfi
/* -----------------------------------------------------
* This cpu has been physically powered up. Depending
@@ -120,9 +121,6 @@
mrs x0, mpidr_el1
bl platform_set_coherent_stack
bl psci_cpu_off
- mov x1, #PSCI_E_SUCCESS
- cmp x0, x1
- b.eq final_wfi
mov sp, x19
ldp x19, x20, [sp,#0]
add sp, sp, #0x10
@@ -144,9 +142,6 @@
mov x1, x21
mov x2, x22
bl psci_cpu_suspend
- mov x1, #PSCI_E_SUCCESS
- cmp x0, x1
- b.eq final_wfi
mov sp, x19
ldp x21, x22, [sp,#0x10]
ldp x19, x20, [sp,#0]
@@ -154,7 +149,16 @@
func_epilogue
ret
-func final_wfi
+ /* --------------------------------------------
+ * This function is called to indicate to the
+ * power controller that it is safe to power
+ * down this cpu. It should not exit the wfi
+ * and will be released from reset upon power
+ * up. 'wfi_spill' is used to catch erroneous
+ * exits from wfi.
+ * --------------------------------------------
+ */
+func psci_power_down_wfi
dsb sy // ensure write buffer empty
wfi
wfi_spill:
diff --git a/services/std_svc/psci/psci_main.c b/services/std_svc/psci/psci_main.c
index 1bcf216..c0866fb 100644
--- a/services/std_svc/psci/psci_main.c
+++ b/services/std_svc/psci/psci_main.c
@@ -90,23 +90,37 @@
if (target_afflvl > MPIDR_MAX_AFFLVL)
return PSCI_E_INVALID_PARAMS;
+ /* Determine the 'state type' in the 'power_state' parameter */
pstate_type = psci_get_pstate_type(power_state);
+
+ /*
+ * Ensure that we have a platform specific handler for entering
+ * a standby state.
+ */
if (pstate_type == PSTATE_TYPE_STANDBY) {
- if (psci_plat_pm_ops->affinst_standby)
- rc = psci_plat_pm_ops->affinst_standby(power_state);
- else
+ if (!psci_plat_pm_ops->affinst_standby)
return PSCI_E_INVALID_PARAMS;
- } else {
- mpidr = read_mpidr();
- rc = psci_afflvl_suspend(mpidr,
- entrypoint,
- context_id,
- power_state,
- MPIDR_AFFLVL0,
- target_afflvl);
+
+ rc = psci_plat_pm_ops->affinst_standby(power_state);
+ assert(rc == PSCI_E_INVALID_PARAMS || rc == PSCI_E_SUCCESS);
+ return rc;
}
- assert(rc == PSCI_E_INVALID_PARAMS || rc == PSCI_E_SUCCESS);
+ /*
+ * Do what is needed to enter the power down state. Upon success,
+ * enter the final wfi which will power down this cpu else return
+ * an error.
+ */
+ mpidr = read_mpidr();
+ rc = psci_afflvl_suspend(mpidr,
+ entrypoint,
+ context_id,
+ power_state,
+ MPIDR_AFFLVL0,
+ target_afflvl);
+ if (rc == PSCI_E_SUCCESS)
+ psci_power_down_wfi();
+ assert(rc == PSCI_E_INVALID_PARAMS);
return rc;
}
@@ -127,10 +141,18 @@
rc = psci_afflvl_off(mpidr, MPIDR_AFFLVL0, target_afflvl);
/*
+ * Check if all actions needed to safely power down this cpu have
+ * successfully completed. Enter a wfi loop which will allow the
+ * power controller to physically power down this cpu.
+ */
+ if (rc == PSCI_E_SUCCESS)
+ psci_power_down_wfi();
+
+ /*
* The only error cpu_off can return is E_DENIED. So check if that's
* indeed the case.
*/
- assert (rc == PSCI_E_SUCCESS || rc == PSCI_E_DENIED);
+ assert (rc == PSCI_E_DENIED);
return rc;
}