regmap: add ARM SMCCC support

Accessing secure controllers can be done by using SMC calls. This regmap
allows to forward register read request to the secure monitor.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>

drivers/base/regmap/Kconfig

@@ -4,7 +4,7 @@
 # subsystems should select the appropriate symbols.
 
 config REGMAP
-	default y if (REGMAP_I2C || REGMAP_SPI || REGMAP_SPMI || REGMAP_W1 || REGMAP_AC97 || REGMAP_MMIO || REGMAP_IRQ || REGMAP_SOUNDWIRE || REGMAP_SOUNDWIRE_MBQ || REGMAP_SCCB || REGMAP_I3C || REGMAP_SPI_AVMM)
+	default y if (REGMAP_I2C || REGMAP_SPI || REGMAP_SPMI || REGMAP_W1 || REGMAP_AC97 || REGMAP_MMIO || REGMAP_IRQ || REGMAP_SOUNDWIRE || REGMAP_SOUNDWIRE_MBQ || REGMAP_SCCB || REGMAP_I3C || REGMAP_SPI_AVMM || REGMAP_SMCCC)
 	select IRQ_DOMAIN if REGMAP_IRQ
 	bool
 
@@ -61,3 +61,8 @@ config REGMAP_I3C
 config REGMAP_SPI_AVMM
 	tristate
 	depends on SPI
+
+config REGMAP_SMCCC
+	default y if HAVE_ARM_SMCCC_DISCOVERY
+	tristate
+	depends on HAVE_ARM_SMCCC_DISCOVERY

drivers/base/regmap/Makefile

@@ -19,3 +19,4 @@ obj-$(CONFIG_REGMAP_SOUNDWIRE_MBQ) += regmap-sdw-mbq.o
 obj-$(CONFIG_REGMAP_SCCB) += regmap-sccb.o
 obj-$(CONFIG_REGMAP_I3C) += regmap-i3c.o
 obj-$(CONFIG_REGMAP_SPI_AVMM) += regmap-spi-avmm.o
+obj-$(CONFIG_REGMAP_SMCCC) += regmap-smccc.o

drivers/base/regmap/regmap-smccc.c

@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018 Synopsys, Inc. and/or its affiliates.
+
+#include <linux/arm-smccc.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#define REGMAP_SMC_READ		0
+#define REGMAP_SMC_WRITE	1
+
+struct regmap_smccc_ctx {
+	u32 regmap_smc_id;
+	u8 val_bytes;
+};
+
+static int regmap_smccc_reg_write(void *context, unsigned int reg,
+				  unsigned int val)
+{
+	struct regmap_smccc_ctx *ctx = context;
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(ctx->regmap_smc_id, REGMAP_SMC_WRITE, reg, val,
+			     &res);
+
+	if (res.a0)
+		return -EACCES;
+
+	return 0;
+}
+
+static int regmap_smccc_reg_read(void *context, unsigned int reg,
+				 unsigned int *val)
+{
+	struct regmap_smccc_ctx *ctx = context;
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(ctx->regmap_smc_id, REGMAP_SMC_READ, reg, &res);
+
+	if (res.a0)
+		return -EACCES;
+
+	*val = res.a1;
+
+	return 0;
+}
+
+static struct regmap_bus regmap_smccc = {
+	.reg_write = regmap_smccc_reg_write,
+	.reg_read = regmap_smccc_reg_read,
+};
+
+static int regmap_smccc_bits_is_supported(int val_bits)
+{
+	switch (val_bits) { 
+	case 8:
+	case 16:
+	case 32:
+		return 0;
+	case 64:
+	/* 
+	 * SMCs are using registers to pass informations so if architecture is
+	 * not using 64 bits registers, we won't be able to pass information
+	 * transparently.
+	 */
+#if !defined(CONFIG_64BIT)
+		return -EINVAL;
+#else
+		return 0;
+#endif
+	default:
+		return -EINVAL;
+	}
+}
+
+static struct regmap_smccc_ctx *smccc_regmap_init_ctx(
+					const struct regmap_config *config,
+				 	u32 regmap_smc_id)
+{
+	int ret;
+	struct regmap_smccc_ctx *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ret = regmap_smccc_bits_is_supported(config->val_bits);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ctx->regmap_smc_id = regmap_smc_id;
+	ctx->val_bytes = config->val_bits / 8;
+
+	return ctx;
+}
+
+struct regmap *__regmap_init_smccc(struct device *dev, u32 regmap_smc_id,
+				   const struct regmap_config *config,
+				   struct lock_class_key *lock_key,
+				   const char *lock_name)
+{
+	struct regmap_smccc_ctx *ctx;
+
+	ctx = smccc_regmap_init_ctx(config, regmap_smc_id);
+	if (IS_ERR(ctx))
+		return ERR_CAST(ctx);
+
+	return __regmap_init(dev, &regmap_smccc, ctx, config, lock_key,
+			     lock_name);
+
+}
+EXPORT_SYMBOL_GPL(__regmap_init_smccc);
+
+struct regmap *__devm_regmap_init_smccc(struct device *dev, u32 regmap_smc_id,
+					const struct regmap_config *config,
+					struct lock_class_key *lock_key,
+					const char *lock_name)
+{
+	struct regmap_smccc_ctx *ctx;
+
+	ctx = smccc_regmap_init_ctx(config, regmap_smc_id);
+	if (IS_ERR(ctx))
+		return ERR_CAST(ctx);
+
+	return __devm_regmap_init(dev, &regmap_smccc, ctx, config, lock_key,
+				  lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_smccc);
+
+MODULE_AUTHOR("Clément Léger <clement.leger@bootlin.com>");
+MODULE_DESCRIPTION("Regmap SMCCC Module");
+MODULE_LICENSE("GPL v2");

include/linux/regmap.h

@@ -584,6 +584,11 @@ struct regmap *__regmap_init_spi_avmm(struct spi_device *spi,
 				      struct lock_class_key *lock_key,
 				      const char *lock_name);
 
+struct regmap *__regmap_init_smccc(struct device *dev, u32 regmap_smc_id,
+				      const struct regmap_config *config,
+				      struct lock_class_key *lock_key,
+				      const char *lock_name);
+
 struct regmap *__devm_regmap_init(struct device *dev,
 				  const struct regmap_bus *bus,
 				  void *bus_context,
@@ -644,6 +649,10 @@ struct regmap *__devm_regmap_init_spi_avmm(struct spi_device *spi,
 					   const struct regmap_config *config,
 					   struct lock_class_key *lock_key,
 					   const char *lock_name);
+struct regmap *__devm_regmap_init_smccc(struct device *dev, u32 regmap_smc_id,
+					const struct regmap_config *config,
+					struct lock_class_key *lock_key,
+					const char *lock_name);
 /*
  * Wrapper for regmap_init macros to include a unique lockdep key and name
  * for each call. No-op if CONFIG_LOCKDEP is not set.
@@ -857,6 +866,20 @@ bool regmap_ac97_default_volatile(struct device *dev, unsigned int reg);
 	__regmap_lockdep_wrapper(__regmap_init_spi_avmm, #config,		\
 				 spi, config)
 
+/**
+ * regmap_init_smccc() - Initialize register map for ARM SMCCC
+ *
+ * @dev: Device that will be interacted with
+ * @smc_id: SMC id to used for calls
+ * @config: Configuration for register map
+ *
+ * The return value will be an ERR_PTR() on error or a valid pointer
+ * to a struct regmap.
+ */
+#define regmap_init_smccc(dev, smc_id, config)			\
+	__regmap_lockdep_wrapper(__regmap_init_smccc, #config,	\
+				 dev, smc_id, config)
+
 /**
  * devm_regmap_init() - Initialise managed register map
  *
@@ -1072,6 +1095,21 @@ bool regmap_ac97_default_volatile(struct device *dev, unsigned int reg);
 	__regmap_lockdep_wrapper(__devm_regmap_init_spi_avmm, #config,	\
 				 spi, config)
 
+/**
+ * devm_regmap_init_smccc() - Initialize register map for ARM SMCCC
+ *
+ * @dev: Device that will be interacted with
+ * @smc_id: SMC id to used for calls
+ * @config: Configuration for register map
+ *
+ * The return value will be an ERR_PTR() on error or a valid pointer
+ * to a struct regmap.  The map will be automatically freed by the
+ * device management code.
+ */
+#define devm_regmap_init_smccc(dev, smc_id, config)			\
+	__regmap_lockdep_wrapper(__devm_regmap_init_smccc, #config,	\
+				 dev, smc_id, config)
+
 int regmap_mmio_attach_clk(struct regmap *map, struct clk *clk);
 void regmap_mmio_detach_clk(struct regmap *map);
 void regmap_exit(struct regmap *map);