drivers: dac: add a driver for the SAM0 DAC

The Atmel SAM0 DAC is a single channel 10 bit DAC with selectable
reference.

Signed-off-by: Michael Hope <mlhx@google.com>

drivers/dac/CMakeLists.txt

@@ -5,5 +5,6 @@ zephyr_library()
 zephyr_library_sources_ifdef(CONFIG_DAC_MCUX_DAC	dac_mcux_dac.c)
 zephyr_library_sources_ifdef(CONFIG_DAC_MCUX_DAC32	dac_mcux_dac32.c)
 zephyr_library_sources_ifdef(CONFIG_DAC_STM32		dac_stm32.c)
+zephyr_library_sources_ifdef(CONFIG_DAC_SAM0		dac_sam0.c)
 zephyr_library_sources_ifdef(CONFIG_DAC_SHELL		dac_shell.c)
 zephyr_library_sources_ifdef(CONFIG_USERSPACE		dac_handlers.c)

drivers/dac/Kconfig

@@ -28,4 +28,6 @@ source "drivers/dac/Kconfig.mcux"
 
 source "drivers/dac/Kconfig.stm32"
 
+source "drivers/dac/Kconfig.sam0"
+
 endif # DAC

drivers/dac/Kconfig.sam0

@@ -0,0 +1,9 @@
+# Copyright (c) 2020 Google LLC
+# SPDX-License-Identifier: Apache-2.0
+
+config DAC_SAM0
+	bool "Atmel SAM0 series DAC Driver"
+	default n
+	depends on SOC_SERIES_SAMD20 || SOC_SERIES_SAMD21
+	help
+	  Enables the Atmel SAM0 MCU Family Digital-to-Analog (DAC) driver.

drivers/dac/dac_sam0.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2020 Google LLC.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT atmel_sam0_dac
+
+#include <errno.h>
+
+#include <drivers/dac.h>
+#include <soc.h>
+
+/*
+ * Maps between the DTS reference property names and register values.  Note that
+ * the ASF uses the 09/2015 names which differ from the 03/2020 datasheet.
+ *
+ * TODO(#21273): replace once improved support for enum values lands.
+ */
+#define SAM0_DAC_REFSEL_0 DAC_CTRLB_REFSEL_INT1V_Val
+#define SAM0_DAC_REFSEL_1 DAC_CTRLB_REFSEL_AVCC_Val
+#define SAM0_DAC_REFSEL_2 DAC_CTRLB_REFSEL_VREFP_Val
+
+struct dac_sam0_cfg {
+	Dac *regs;
+	uint8_t pm_apbc_bit;
+	uint8_t gclk_clkctrl_id;
+	uint8_t refsel;
+};
+
+#define DEV_CFG(dev) ((const struct dac_sam0_cfg *const)(dev)->config_info)
+
+/* Write to the DAC. */
+static int dac_sam0_write_value(struct device *dev, uint8_t channel,
+				uint32_t value)
+{
+	const struct dac_sam0_cfg *const cfg = DEV_CFG(dev);
+	Dac *regs = cfg->regs;
+
+	regs->DATA.reg = (uint16_t)value;
+
+	return 0;
+}
+
+/*
+ * Setup the channel.  As the SAM0 has one fixed width channel, this validates
+ * the input and does nothing else.
+ */
+static int dac_sam0_channel_setup(struct device *dev,
+				  const struct dac_channel_cfg *channel_cfg)
+{
+	if (channel_cfg->channel_id != 0) {
+		return -EINVAL;
+	}
+	if (channel_cfg->resolution != 10) {
+		return -ENOTSUP;
+	}
+
+	return 0;
+}
+
+/* Initialise and enable the DAC. */
+static int dac_sam0_init(struct device *dev)
+{
+	const struct dac_sam0_cfg *const cfg = DEV_CFG(dev);
+	Dac *regs = cfg->regs;
+
+	/* Enable the GCLK */
+	GCLK->CLKCTRL.reg = cfg->gclk_clkctrl_id | GCLK_CLKCTRL_GEN_GCLK0 |
+			    GCLK_CLKCTRL_CLKEN;
+
+	/* Enable the clock in PM */
+	PM->APBCMASK.reg |= 1 << cfg->pm_apbc_bit;
+
+	/* Reset then configure the DAC */
+	regs->CTRLA.bit.SWRST = 1;
+	while (regs->STATUS.bit.SYNCBUSY) {
+	}
+
+	regs->CTRLB.bit.REFSEL = cfg->refsel;
+	regs->CTRLB.bit.EOEN = 1;
+
+	/* Enable */
+	regs->CTRLA.bit.ENABLE = 1;
+	while (regs->STATUS.bit.SYNCBUSY) {
+	}
+
+	return 0;
+}
+
+static const struct dac_driver_api api_sam0_driver_api = {
+	.channel_setup = dac_sam0_channel_setup,
+	.write_value = dac_sam0_write_value
+};
+
+#define SAM0_DAC_REFSEL(n)						       \
+	COND_CODE_1(DT_INST_NODE_HAS_PROP(n, reference),		       \
+		    (DT_ENUM_IDX(DT_DRV_INST(n), reference)), (0))
+
+#define SAM0_DAC_INIT(n)						       \
+	static const struct dac_sam0_cfg dac_sam0_cfg_##n = {		       \
+		.regs = (Dac *)DT_INST_REG_ADDR(n),			       \
+		.pm_apbc_bit = DT_INST_CLOCKS_CELL_BY_NAME(n, pm, bit),	       \
+		.gclk_clkctrl_id =					       \
+			DT_INST_CLOCKS_CELL_BY_NAME(n, gclk, clkctrl_id),      \
+		.refsel = UTIL_CAT(SAM0_DAC_REFSEL_, SAM0_DAC_REFSEL(n)),      \
+	};								       \
+									       \
+	DEVICE_AND_API_INIT(dac_##n, DT_INST_LABEL(n), &dac_sam0_init, NULL,   \
+			    &dac_sam0_cfg_##n, POST_KERNEL,		       \
+			    CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,	       \
+			    &api_sam0_driver_api)
+
+DT_INST_FOREACH_STATUS_OKAY(SAM0_DAC_INIT);

soc/arm/atmel_sam0/common/Kconfig.defconfig.series

@@ -11,6 +11,9 @@ config ADC_SAM0
 config COUNTER_SAM0_TC32
 	default COUNTER
 
+config DAC_SAM0
+	default DAC
+
 config DMA_SAM0
 	default DMA