PSCI: Optimize call paths if all participants are cache-coherent

The current PSCI implementation can apply certain optimizations upon the
assumption that all PSCI participants are cache-coherent.

  - Skip performing cache maintenance during power-up.

  - Skip performing cache maintenance during power-down:

    At present, on the power-down path, CPU driver disables caches and
    MMU, and performs cache maintenance in preparation for powering down
    the CPU. This means that PSCI must perform additional cache
    maintenance on the extant stack for correct functioning.

    If all participating CPUs are cache-coherent, CPU driver would
    neither disable MMU nor perform cache maintenance. The CPU being
    powered down, therefore, remain cache-coherent throughout all PSCI
    call paths. This in turn means that PSCI cache maintenance
    operations are not required during power down.

  - Choose spin locks instead of bakery locks:

    The current PSCI implementation must synchronize both cache-coherent
    and non-cache-coherent participants. Mutual exclusion primitives are
    not guaranteed to function on non-coherent memory. For this reason,
    the current PSCI implementation had to resort to bakery locks.

    If all participants are cache-coherent, the implementation can
    enable MMU and data caches early, and substitute bakery locks for
    spin locks. Spin locks make use of architectural mutual exclusion
    primitives, and are lighter and faster.

The optimizations are applied when HW_ASSISTED_COHERENCY build option is
enabled, as it's expected that all PSCI participants are cache-coherent
in those systems.

Change-Id: Iac51c3ed318ea7e2120f6b6a46fd2db2eae46ede
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

1 files changed, 5 insertions, 9 deletions

diff --git a/lib/psci/psci_suspend.c b/lib/psci/psci_suspend.c
index 23e5adab..08c8fd6a 100644
--- a/lib/psci/psci_suspend.c
+++ b/lib/psci/psci_suspend.c
@@ -121,13 +121,11 @@ static void psci_suspend_to_pwrdown_start(unsigned int end_pwrlvl,
 #endif
 
 	/*
-	 * Arch. management. Perform the necessary steps to flush all
-	 * cpu caches. Currently we assume that the power level correspond
-	 * the cache level.
+	 * Arch. management. Initiate power down sequence.
 	 * TODO : Introduce a mechanism to query the cache level to flush
 	 * and the cpu-ops power down to perform from the platform.
 	 */
-	psci_do_pwrdown_cache_maintenance(max_off_lvl);
+	psci_do_pwrdown_sequence(max_off_lvl);
 
 #if ENABLE_RUNTIME_INSTRUMENTATION
 	PMF_CAPTURE_TIMESTAMP(rt_instr_svc,
@@ -304,12 +302,10 @@ void psci_cpu_suspend_finish(unsigned int cpu_idx,
 	 */
 	psci_plat_pm_ops->pwr_domain_suspend_finish(state_info);
 
-	/*
-	 * Arch. management: Enable the data cache, manage stack memory and
-	 * restore the stashed EL3 architectural context from the 'cpu_context'
-	 * structure for this cpu.
-	 */
+#if !HW_ASSISTED_COHERENCY
+	/* Arch. management: Enable the data cache, stack memory maintenance. */
 	psci_do_pwrup_cache_maintenance();
+#endif
 
 	/* Re-init the cntfrq_el0 register */
 	counter_freq = plat_get_syscnt_freq2();