drivers: syscon: Add generic syscon API

A syscon device is a device managing a memory region containing a set of
registers that are not cohesive enough to represent as any specific type
of device. We need a driver for that because several other drivers could
use the same region at the same time and we need to io-map the region at
boot for MMU enabled platforms.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

CODEOWNERS

@@ -186,6 +186,7 @@
 /drivers/adc/adc_stm32.c                  @cybertale
 /drivers/bluetooth/                       @joerchan @jhedberg @Vudentz
 /drivers/cache/                           @carlocaione
+/drivers/syscon/                          @carlocaione
 /drivers/can/                             @alexanderwachter
 /drivers/can/*mcp2515*                    @karstenkoenig
 /drivers/can/*rcar*                       @julien-massot

drivers/CMakeLists.txt

@@ -57,3 +57,4 @@ add_subdirectory_ifdef(CONFIG_NEURAL_NET_ACCEL neural_net)
 add_subdirectory_ifdef(CONFIG_PTP_CLOCK        ptp_clock)
 add_subdirectory_ifdef(CONFIG_EDAC             edac)
 add_subdirectory_ifdef(CONFIG_CACHE_MANAGEMENT cache)
+add_subdirectory_ifdef(CONFIG_SYSCON           syscon)

drivers/Kconfig

@@ -115,4 +115,6 @@ source "drivers/disk/Kconfig"
 
 source "drivers/cache/Kconfig"
 
+source "drivers/syscon/Kconfig"
+
 endmenu

drivers/syscon/CMakeLists.txt

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_sources_ifdef(CONFIG_SYSCON          syscon.c)

drivers/syscon/Kconfig

@@ -0,0 +1,43 @@
+# SYSCON configuration options
+
+# Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+# SPDX-License-Identifier: Apache-2.0
+
+#
+# SYSCON options
+#
+menuconfig SYSCON
+	bool "SYSCON (System Controller) drivers"
+	help
+	  SYSCON (System Controller) drivers. System controller node represents
+	  a register region containing a set of miscellaneous registers. The
+	  registers are not cohesive enough to represent as any specific type
+	  of device. The typical use-case is for some other node's driver, or
+	  platform-specific code, to acquire a reference to the syscon node and
+	  extract information from there.
+
+if SYSCON
+
+module = SYSCON
+module-str = syscon
+source "subsys/logging/Kconfig.template.log_config"
+
+DT_COMPAT_SYSCON := syscon
+
+config SYSCON_GENERIC
+	bool "Generic SYSCON (System Controller) driver"
+	default $(dt_compat_enabled,$(DT_COMPAT_SYSCON))
+	help
+	  Enable generic SYSCON (System Controller) driver
+
+config SYSCON_GENERIC_INIT_PRIORITY_DEVICE
+	int "SYSCON (System Controller) generic init device priority"
+	default 50
+	depends on SYSCON_GENERIC
+	help
+	  This option controls the priority of the syscon device
+	  initialization. Higher priority ensures that the device is
+	  initialized earlier in the startup cycle. If unsure, leave at default
+	  value
+
+endif # SYSCON

drivers/syscon/syscon.c

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) Carlo Caione <ccaione@baylibre.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT syscon
+
+#include <sys/util.h>
+#include <device.h>
+#include <init.h>
+
+#include <drivers/syscon.h>
+
+static const struct device *syscon_dev;
+
+struct syscon_generic_config {
+	DEVICE_MMIO_ROM;
+};
+
+static struct syscon_generic_config syscon_generic_config_0 = {
+	DEVICE_MMIO_ROM_INIT(DT_DRV_INST(0)),
+};
+
+struct syscon_generic_data {
+	DEVICE_MMIO_RAM;
+	size_t size;
+};
+
+static struct syscon_generic_data syscon_generic_data_0;
+
+uintptr_t syscon_generic_get_base(void)
+{
+	if (!syscon_dev) {
+		return -ENODEV;
+	}
+
+	return DEVICE_MMIO_GET(syscon_dev);
+}
+
+static int sanitize_reg(uint16_t *reg, size_t reg_size)
+{
+	/* Avoid unaligned readings */
+	*reg = ROUND_DOWN(*reg, sizeof(uint32_t));
+
+	/* Check for out-of-bounds readings */
+	if (*reg >= reg_size) {
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+int syscon_generic_read_reg(uint16_t reg, uint32_t *val)
+{
+	struct syscon_generic_data *data;
+	uintptr_t base_address;
+
+	if (!syscon_dev) {
+		return -ENODEV;
+	}
+
+	data = syscon_dev->data;
+
+	if (!val) {
+		return -EINVAL;
+	}
+
+	if (sanitize_reg(&reg, data->size)) {
+		return -EINVAL;
+	}
+
+	base_address = DEVICE_MMIO_GET(syscon_dev);
+
+	*val = sys_read32(base_address + reg);
+
+	return 0;
+}
+
+int syscon_generic_write_reg(uint16_t reg, uint32_t val)
+{
+	struct syscon_generic_data *data;
+	uintptr_t base_address;
+
+	if (!syscon_dev) {
+		return -ENODEV;
+	}
+
+	data = syscon_dev->data;
+
+	if (sanitize_reg(&reg, data->size)) {
+		return -EINVAL;
+	}
+
+	base_address = DEVICE_MMIO_GET(syscon_dev);
+
+	sys_write32(val, (base_address + reg));
+
+	return 0;
+}
+
+int syscon_generic_init(const struct device *dev)
+{
+	struct syscon_generic_data *data = dev->data;
+
+	syscon_dev = dev;
+
+	DEVICE_MMIO_MAP(syscon_dev, K_MEM_CACHE_NONE);
+
+	data->size = DT_REG_SIZE(DT_DRV_INST(0));
+
+	return 0;
+}
+
+DEVICE_DT_INST_DEFINE(0, syscon_generic_init, NULL, &syscon_generic_data_0,
+		&syscon_generic_config_0, PRE_KERNEL_1,
+		CONFIG_SYSCON_GENERIC_INIT_PRIORITY_DEVICE, NULL);

dts/bindings/syscon/syscon.yaml

@@ -0,0 +1,12 @@
+# Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+# SPDX-License-Identifier: Apache-2.0
+
+description: System Controller Registers R/W
+
+compatible: "syscon"
+
+include: base.yaml
+
+properties:
+    reg:
+      required: true

include/drivers/syscon.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ * @brief Public SYSCON driver APIs
+ */
+
+#ifndef ZEPHYR_INCLUDE_DRIVERS_SYSCON_H_
+#define ZEPHYR_INCLUDE_DRIVERS_SYSCON_H_
+
+/**
+ * @brief SYSCON Interface
+ * @defgroup syscon_interface SYSCON Interface
+ * @ingroup io_interfaces
+ * @{
+ */
+
+#include <zephyr/types.h>
+#include <device.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Get the syscon base address
+ *
+ * This function returns the syscon base address
+ *
+ * @return 0 on error, the base address on success
+ */
+uintptr_t syscon_get_base(void);
+
+/**
+ * @brief Read from syscon register
+ *
+ * This function reads from a specific register in the syscon area
+ *
+ * @param reg The register offset
+ * @param val The returned value read from the syscon register
+ *
+ * @return 0 on success, negative on error
+ */
+int syscon_read_reg(uint16_t reg, uint32_t *val);
+
+/**
+ * @brief Write to syscon register
+ *
+ * This function writes to a specific register in the syscon area
+ *
+ * @param reg The register offset
+ * @param val The value to be written in the register
+ *
+ * @return 0 on success, negative on error
+ */
+int syscon_write_reg(uint16_t reg, uint32_t val);
+
+/**
+ * @}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	/* ZEPHYR_INCLUDE_DRIVERS_SYSCON_H_ */