firmware: arm_ffa: Add support for SMCCC as transport to FFA driver

There are requests to keep the transport separate in order to allow
other possible transports like virtio. So let us keep the SMCCC transport
specific routines abstracted.

It is kept simple for now. Once we add another transport, we can develop
better abstraction.

Link: https://lore.kernel.org/r/20210521151033.181846-4-sudeep.holla@arm.com
Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_ffa/Kconfig

@@ -14,3 +14,8 @@ config ARM_FFA_TRANSPORT
 
 	  This driver provides interface for all the client drivers making
 	  use of the features offered by ARM FF-A.
+
+config ARM_FFA_SMCCC
+	bool
+	default ARM_FFA_TRANSPORT
+	depends on ARM64 && HAVE_ARM_SMCCC_DISCOVERY

drivers/firmware/arm_ffa/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 ffa-bus-y = bus.o
 ffa-driver-y = driver.o
-ffa-module-objs := $(ffa-bus-y) $(ffa-driver-y)
+ffa-transport-$(CONFIG_ARM_FFA_SMCCC) += smccc.o
+ffa-module-objs := $(ffa-bus-y) $(ffa-driver-y) $(ffa-transport-y)
 obj-$(CONFIG_ARM_FFA_TRANSPORT) = ffa-module.o

drivers/firmware/arm_ffa/common.h

@@ -16,9 +16,13 @@ typedef void (ffa_fn)(ffa_value_t, ffa_value_t *);
 int arm_ffa_bus_init(void);
 void arm_ffa_bus_exit(void);
 
+#ifdef CONFIG_ARM_FFA_SMCCC
+int __init ffa_transport_init(ffa_fn **invoke_ffa_fn);
+#else
 static inline int __init ffa_transport_init(ffa_fn **invoke_ffa_fn)
 {
 	return -EOPNOTSUPP;
 }
+#endif
 
 #endif /* _FFA_COMMON_H */

drivers/firmware/arm_ffa/smccc.c

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 ARM Ltd.
+ */
+
+#include <linux/printk.h>
+
+#include "common.h"
+
+static void __arm_ffa_fn_smc(ffa_value_t args, ffa_value_t *res)
+{
+	arm_smccc_1_2_smc(&args, res);
+}
+
+static void __arm_ffa_fn_hvc(ffa_value_t args, ffa_value_t *res)
+{
+	arm_smccc_1_2_hvc(&args, res);
+}
+
+int __init ffa_transport_init(ffa_fn **invoke_ffa_fn)
+{
+	enum arm_smccc_conduit conduit;
+
+	if (arm_smccc_get_version() < ARM_SMCCC_VERSION_1_2)
+		return -EOPNOTSUPP;
+
+	conduit = arm_smccc_1_1_get_conduit();
+	if (conduit == SMCCC_CONDUIT_NONE) {
+		pr_err("%s: invalid SMCCC conduit\n", __func__);
+		return -EOPNOTSUPP;
+	}
+
+	if (conduit == SMCCC_CONDUIT_SMC)
+		*invoke_ffa_fn = __arm_ffa_fn_smc;
+	else
+		*invoke_ffa_fn = __arm_ffa_fn_hvc;
+
+	return 0;
+}