[RFC PATCH v2 1/6] firmware: helper functions for SMCCC v1.0 invocation conduit

[Etienne Carriere]

Introduce invocation helper functions based on existing arm_smccc_1_1_*()
helpers but for drivers that interact with a firmware supporting Arm
SMCCC specification v1.0 but not v1.1.

This change allows devices not defining a SMCCC conduit method to
leverage the conduit defined by early initialized PSCI generic driver
when secure firmware does not support SMCCC v1.1.

This change allows devices to ensure consistency of the conduit
used among drivers defining a conduit method. Indeed, at runtime, all
devices are expected to use the very same SMCCC invocation conduit:
HVC or SMC.

Signed-off-by: Etienne Carriere <etienne.carriere@xxxxxxxxxx>
---
 drivers/firmware/Makefile            |   1 +
 drivers/firmware/arm_smccc_conduit.c | 148 +++++++++++++++++++++++++++
 include/linux/arm-smccc.h            | 106 +++++++++++++++++++
 3 files changed, 255 insertions(+)
 create mode 100644 drivers/firmware/arm_smccc_conduit.c

diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index e9fb838af4df..5a4a72a06346 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -5,6 +5,7 @@
 obj-$(CONFIG_ARM_SCPI_PROTOCOL)	+= arm_scpi.o
 obj-$(CONFIG_ARM_SCPI_POWER_DOMAIN) += scpi_pm_domain.o
 obj-$(CONFIG_ARM_SDE_INTERFACE)	+= arm_sdei.o
+obj-$(CONFIG_HAVE_ARM_SMCCC)	+= arm_smccc_conduit.o
 obj-$(CONFIG_DMI)		+= dmi_scan.o
 obj-$(CONFIG_DMI_SYSFS)		+= dmi-sysfs.o
 obj-$(CONFIG_EDD)		+= edd.o
diff --git a/drivers/firmware/arm_smccc_conduit.c b/drivers/firmware/arm_smccc_conduit.c
new file mode 100644
index 000000000000..fd402fec89dd
--- /dev/null
+++ b/drivers/firmware/arm_smccc_conduit.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020, Linaro Limited
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/device.h>
+#include <linux/of.h>
+
+static enum arm_smccc_conduit arm_smccc_1_0_conduit = SMCCC_CONDUIT_NONE;
+
+/* Helpers for nice trace when called outside a device instance */
+#define PRINT_INFO(dev, ...)				\
+	do {						\
+		if (dev)				\
+			dev_info(dev, __VA_ARGS__);	\
+		else					\
+			pr_info(__VA_ARGS__);		\
+	} while (0)
+
+#define PRINT_WARN(dev, ...)				\
+	do {						\
+		if (dev)				\
+			dev_warn(dev, __VA_ARGS__);	\
+		else					\
+			pr_warn(__VA_ARGS__);		\
+	} while (0)
+
+#define PRINT_ERROR(dev, ...)				\
+	do {						\
+		if (dev)				\
+			dev_err(dev, __VA_ARGS__);	\
+		else					\
+			pr_err(__VA_ARGS__);		\
+	} while (0)
+
+static const char *conduit_str(enum arm_smccc_conduit conduit)
+{
+	static const char hvc_str[] = "HVC";
+	static const char smc_str[] = "SMC";
+	static const char unknown[] = "unknown";
+
+	switch (conduit) {
+	case SMCCC_CONDUIT_HVC:
+		return hvc_str;
+	case SMCCC_CONDUIT_SMC:
+		return smc_str;
+	default:
+		return unknown;
+	}
+}
+
+static int set_conduit(struct device *dev, enum arm_smccc_conduit conduit)
+{
+	switch (conduit) {
+	case SMCCC_CONDUIT_HVC:
+	case SMCCC_CONDUIT_SMC:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (arm_smccc_1_0_conduit == SMCCC_CONDUIT_NONE) {
+		arm_smccc_1_0_conduit = conduit;
+		return 0;
+	}
+
+	if (conduit == arm_smccc_1_0_conduit)
+		return 0;
+
+	PRINT_ERROR(dev, "inconsistent conduits %u (%s) vs %u (%s)\n",
+		    conduit, conduit_str(conduit),
+		    arm_smccc_1_0_conduit, conduit_str(arm_smccc_1_0_conduit));
+
+	return -EINVAL;
+}
+
+static enum arm_smccc_conduit method_to_conduit(const char *method)
+{
+	if (!strcmp("hvc", method))
+		return SMCCC_CONDUIT_HVC;
+	else if (!strcmp("smc", method))
+		return SMCCC_CONDUIT_SMC;
+	else
+		return SMCCC_CONDUIT_NONE;
+}
+
+static int set_conduit_from_node(struct device *dev, struct device_node *np)
+{
+	const char *method;
+
+	PRINT_INFO(dev, "probing for conduit method from DT.\n");
+
+	if (!np)
+		return -EINVAL;
+
+	if (!of_property_read_string(np, "method", &method)) {
+		enum arm_smccc_conduit dev_conduit = method_to_conduit(method);
+
+		if (dev_conduit == SMCCC_CONDUIT_NONE) {
+			PRINT_WARN(dev, "invalid \"method\" property \"%s\"\n",
+				   method);
+			return -EINVAL;
+		}
+
+		return set_conduit(dev, dev_conduit);
+	}
+
+	if (arm_smccc_1_0_conduit != SMCCC_CONDUIT_NONE)
+		return 0;
+
+	PRINT_WARN(dev, "missing \"method\" property\n");
+
+	return -ENXIO;
+}
+
+int devm_arm_smccc_1_0_set_conduit(struct device *dev)
+{
+	if (!dev || !dev->of_node)
+		return -EINVAL;
+
+	return set_conduit_from_node(dev, dev->of_node);
+}
+EXPORT_SYMBOL_GPL(devm_arm_smccc_1_0_set_conduit);
+
+int of_arm_smccc_1_0_set_conduit(struct device_node *np)
+{
+	if (!np)
+		return -EINVAL;
+
+	return set_conduit_from_node(NULL, np);
+}
+EXPORT_SYMBOL_GPL(of_arm_smccc_1_0_set_conduit);
+
+int arm_smccc_1_0_set_conduit(enum arm_smccc_conduit conduit)
+{
+	if (set_conduit(NULL, conduit))
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(arm_smccc_1_0_set_conduit);
+
+enum arm_smccc_conduit arm_smccc_1_0_get_conduit(void)
+{
+	return arm_smccc_1_0_conduit;
+}
+EXPORT_SYMBOL_GPL(arm_smccc_1_0_get_conduit);
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 59494df0f55b..2da2b4bd3985 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -377,5 +377,111 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
 			   ARM_SMCCC_OWNER_STANDARD_HYP,	\
 			   0x21)
 
+/* SMCCC v1.0 compliant invocation helpers */
+
+/*
+ * Like arm_smccc_1_0* but always returns SMCCC_RET_NOT_SUPPORTED.
+ * Used when the SMCCC conduit is not defined. The empty asm statement
+ * avoids compiler warnings about unused variables.
+ */
+#define __fail_smccc_1_0(...)						\
+	do {								\
+		__declare_args(7, __VA_ARGS__);				\
+		asm ("" __constraints(7));				\
+		___res->a0 = SMCCC_RET_NOT_SUPPORTED;			\
+	} while (0)
+
+/*
+ * arm_smccc_1_0_invoke() - make an SMCCC v1.0 compliant call
+ *
+ * This is a macro taking eight source arguments and an return structure.
+ * It uses the SMCCC conduit registered during driver(s) initialization.
+ *
+ * @a0-a7: arguments passed in registers 0 to 7
+ * @res: result values from registers 0 to 3
+ *
+ * This macro will make either an HVC call or an SMC call depending on the
+ * specified SMCCC conduit. If no valid conduit is available then -1
+ * (SMCCC_RET_NOT_SUPPORTED) is returned in @res.a0.
+ *
+ * The return value provides the conduit that was used.
+ */
+#define arm_smccc_1_0_invoke(...) ({					\
+		enum arm_smccc_conduit conduit = arm_smccc_1_0_get_conduit(); \
+		switch (conduit) {					\
+		case SMCCC_CONDUIT_HVC:					\
+			arm_smccc_hvc(__VA_ARGS__);			\
+			break;						\
+		case SMCCC_CONDUIT_SMC:					\
+			arm_smccc_smc(__VA_ARGS__);			\
+			break;						\
+		default:						\
+			__fail_smccc_1_0(__VA_ARGS__);			\
+			conduit = SMCCC_CONDUIT_NONE;			\
+		}							\
+		conduit;						\
+	})
+
+struct device;
+struct device_node;
+
+#ifdef CONFIG_HAVE_ARM_SMCCC
+/**
+ * arm_smccc_1_0_get_conduit() - Return registered SMCCC conduit
+ */
+enum arm_smccc_conduit arm_smccc_1_0_get_conduit(void);
+
+/**
+ * arm_smccc_1_0_set_conduit - Register SMCCC invocation conduit
+ * @conduit: conduit to register
+ *
+ * Return 0 on success and -EINVAL on failure.
+ */
+int arm_smccc_1_0_set_conduit(enum arm_smccc_conduit conduit);
+
+/**
+ * devm_arm_smccc_1_0_set_conduit() - Set SMCCC v1.0 conduit if found in device
+ * @dev: Device instance
+ *
+ * Set the SMCCC invocation conduit based on device node if it has a "method"
+ * property that defines the SMCCC conduit to be used. If it has not, check a
+ * conduit is already registered.
+ *
+ * Return 0 on success, -ENXIO if no conduit found, -EINVAL otherwise.
+ */
+int devm_arm_smccc_1_0_set_conduit(struct device *dev);
+
+/**
+ * of_arm_smccc_1_0_set_conduit() - Set SMCCC v1.0 conduit if found in FDT node
+ * @np: Node instance
+ *
+ * Set the SMCCC invocation conduit based on device node if it has a "method"
+ * property that defines the SMCCC conduit to be used. If it has not, check a
+ * conduit is already registered.
+ *
+ * Return 0 on success, -ENXIO if no conduit found, -EINVAL otherwise.
+ */
+int of_arm_smccc_1_0_set_conduit(struct device_node *np);
+#else
+static inline enum arm_smccc_conduit arm_smccc_1_0_get_conduit(void)
+{
+	return SMCCC_CONDUIT_NONE;
+}
+
+static inline int arm_smccc_1_0_set_conduit(enum arm_smccc_conduit conduit)
+{
+	return -ENXIO;
+}
+
+static inline int devm_arm_smccc_1_0_set_conduit(struct device *dev)
+{
+	return -ENXIO;
+}
+
+static inline int of_arm_smccc_1_0_set_conduit(struct device_node *np)
+{
+	return -ENXIO;
+}
+#endif /* CONFIG_HAVE_ARM_SMCCC */
 #endif /*__ASSEMBLY__*/
 #endif /*__LINUX_ARM_SMCCC_H*/
-- 
2.17.1