drivers: firmware: psci: add PSCI_FEATURES call

PSCI v1.0 introduces a PSCI_FEATURES call that allows to probe for
features related to a specific function identifier.

This patch adds PSCI_FEATURES support to the PSCI firmware layer.
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Jisheng Zhang <jszhang@marvell.com>
Cc: Mark Rutland <mark.rutland@arm.com>

drivers/firmware/psci.c

@@ -197,6 +197,12 @@ static void psci_sys_poweroff(void)
 	invoke_psci_fn(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
 }
 
+static int __init psci_features(u32 psci_func_id)
+{
+	return invoke_psci_fn(PSCI_1_0_FN_PSCI_FEATURES,
+			      psci_func_id, 0, 0);
+}
+
 /*
  * Detect the presence of a resident Trusted OS which may cause CPU_OFF to
  * return DENIED (which would be fatal).

include/uapi/linux/psci.h

@@ -46,6 +46,8 @@
 #define PSCI_0_2_FN64_MIGRATE			PSCI_0_2_FN64(5)
 #define PSCI_0_2_FN64_MIGRATE_INFO_UP_CPU	PSCI_0_2_FN64(7)
 
+#define PSCI_1_0_FN_PSCI_FEATURES		PSCI_0_2_FN(10)
+
 /* PSCI v0.2 power state encoding for CPU_SUSPEND function */
 #define PSCI_0_2_POWER_STATE_ID_MASK		0xffff
 #define PSCI_0_2_POWER_STATE_ID_SHIFT		0