spi: offload-trigger: add PWM trigger driver

Add a new driver for a generic PWM trigger for SPI offloads.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250207-dlech-mainline-spi-engine-offload-2-v8-4-e48a489be48c@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

MAINTAINERS

@@ -22297,6 +22297,7 @@ F:	include/linux/mtd/spi-nor.h
 
 SPI OFFLOAD
 R:	David Lechner <dlechner@baylibre.com>
+F:	drivers/spi/spi-offload-trigger-pwm.c
 F:	drivers/spi/spi-offload.c
 F:	include/linux/spi/spi-offload.h
 K:	spi_offload

drivers/spi/Kconfig

@@ -1320,4 +1320,16 @@ endif # SPI_SLAVE
 config SPI_DYNAMIC
 	def_bool ACPI || OF_DYNAMIC || SPI_SLAVE
 
+if SPI_OFFLOAD
+
+comment "SPI Offload triggers"
+
+config SPI_OFFLOAD_TRIGGER_PWM
+	tristate "SPI offload trigger using PWM"
+	depends on PWM
+	help
+	  Generic SPI offload trigger implemented using PWM output.
+
+endif # SPI_OFFLOAD
+
 endif # SPI

drivers/spi/Makefile

@@ -164,3 +164,6 @@ obj-$(CONFIG_SPI_AMD)			+= spi-amd.o
 # SPI slave protocol handlers
 obj-$(CONFIG_SPI_SLAVE_TIME)		+= spi-slave-time.o
 obj-$(CONFIG_SPI_SLAVE_SYSTEM_CONTROL)	+= spi-slave-system-control.o
+
+# SPI offload triggers
+obj-$(CONFIG_SPI_OFFLOAD_TRIGGER_PWM)	+= spi-offload-trigger-pwm.o

drivers/spi/spi-offload-trigger-pwm.c

@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Analog Devices Inc.
+ * Copyright (C) 2024 BayLibre, SAS
+ *
+ * Generic PWM trigger for SPI offload.
+ */
+
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/mod_devicetable.h>
+#include <linux/spi/offload/provider.h>
+#include <linux/types.h>
+
+struct spi_offload_trigger_pwm_state {
+	struct device *dev;
+	struct pwm_device *pwm;
+};
+
+static bool spi_offload_trigger_pwm_match(struct spi_offload_trigger *trigger,
+					  enum spi_offload_trigger_type type,
+					  u64 *args, u32 nargs)
+{
+	if (nargs)
+		return false;
+
+	return type == SPI_OFFLOAD_TRIGGER_PERIODIC;
+}
+
+static int spi_offload_trigger_pwm_validate(struct spi_offload_trigger *trigger,
+					    struct spi_offload_trigger_config *config)
+{
+	struct spi_offload_trigger_pwm_state *st = spi_offload_trigger_get_priv(trigger);
+	struct spi_offload_trigger_periodic *periodic = &config->periodic;
+	struct pwm_waveform wf = { };
+	int ret;
+
+	if (config->type != SPI_OFFLOAD_TRIGGER_PERIODIC)
+		return -EINVAL;
+
+	if (!periodic->frequency_hz)
+		return -EINVAL;
+
+	wf.period_length_ns = DIV_ROUND_UP_ULL(NSEC_PER_SEC, periodic->frequency_hz);
+	/* REVISIT: 50% duty-cycle for now - may add config parameter later */
+	wf.duty_length_ns = wf.period_length_ns / 2;
+
+	ret = pwm_round_waveform_might_sleep(st->pwm, &wf);
+	if (ret < 0)
+		return ret;
+
+	periodic->frequency_hz = DIV_ROUND_UP_ULL(NSEC_PER_SEC, wf.period_length_ns);
+
+	return 0;
+}
+
+static int spi_offload_trigger_pwm_enable(struct spi_offload_trigger *trigger,
+					  struct spi_offload_trigger_config *config)
+{
+	struct spi_offload_trigger_pwm_state *st = spi_offload_trigger_get_priv(trigger);
+	struct spi_offload_trigger_periodic *periodic = &config->periodic;
+	struct pwm_waveform wf = { };
+
+	if (config->type != SPI_OFFLOAD_TRIGGER_PERIODIC)
+		return -EINVAL;
+
+	if (!periodic->frequency_hz)
+		return -EINVAL;
+
+	wf.period_length_ns = DIV_ROUND_UP_ULL(NSEC_PER_SEC, periodic->frequency_hz);
+	/* REVISIT: 50% duty-cycle for now - may add config parameter later */
+	wf.duty_length_ns = wf.period_length_ns / 2;
+
+	return pwm_set_waveform_might_sleep(st->pwm, &wf, false);
+}
+
+static void spi_offload_trigger_pwm_disable(struct spi_offload_trigger *trigger)
+{
+	struct spi_offload_trigger_pwm_state *st = spi_offload_trigger_get_priv(trigger);
+	struct pwm_waveform wf;
+	int ret;
+
+	ret = pwm_get_waveform_might_sleep(st->pwm, &wf);
+	if (ret < 0) {
+		dev_err(st->dev, "failed to get waveform: %d\n", ret);
+		return;
+	}
+
+	wf.duty_length_ns = 0;
+
+	ret = pwm_set_waveform_might_sleep(st->pwm, &wf, false);
+	if (ret < 0)
+		dev_err(st->dev, "failed to disable PWM: %d\n", ret);
+}
+
+static const struct spi_offload_trigger_ops spi_offload_trigger_pwm_ops = {
+	.match = spi_offload_trigger_pwm_match,
+	.validate = spi_offload_trigger_pwm_validate,
+	.enable = spi_offload_trigger_pwm_enable,
+	.disable = spi_offload_trigger_pwm_disable,
+};
+
+static void spi_offload_trigger_pwm_release(void *data)
+{
+	pwm_disable(data);
+}
+
+static int spi_offload_trigger_pwm_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct spi_offload_trigger_info info = {
+		.fwnode = dev_fwnode(dev),
+		.ops = &spi_offload_trigger_pwm_ops,
+	};
+	struct spi_offload_trigger_pwm_state *st;
+	struct pwm_state state;
+	int ret;
+
+	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return -ENOMEM;
+
+	info.priv = st;
+	st->dev = dev;
+
+	st->pwm = devm_pwm_get(dev, NULL);
+	if (IS_ERR(st->pwm))
+		return dev_err_probe(dev, PTR_ERR(st->pwm), "failed to get PWM\n");
+
+	/* init with duty_cycle = 0, output enabled to ensure trigger off */
+	pwm_init_state(st->pwm, &state);
+	state.enabled = true;
+
+	ret = pwm_apply_might_sleep(st->pwm, &state);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to apply PWM state\n");
+
+	ret = devm_add_action_or_reset(dev, spi_offload_trigger_pwm_release, st->pwm);
+	if (ret)
+		return ret;
+
+	return devm_spi_offload_trigger_register(dev, &info);
+}
+
+static const struct of_device_id spi_offload_trigger_pwm_of_match_table[] = {
+	{ .compatible = "pwm-trigger" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, spi_offload_trigger_pwm_of_match_table);
+
+static struct platform_driver spi_offload_trigger_pwm_driver = {
+	.driver = {
+		.name = "pwm-trigger",
+		.of_match_table = spi_offload_trigger_pwm_of_match_table,
+	},
+	.probe = spi_offload_trigger_pwm_probe,
+};
+module_platform_driver(spi_offload_trigger_pwm_driver);
+
+MODULE_AUTHOR("David Lechner <dlechner@baylibre.com>");
+MODULE_DESCRIPTION("Generic PWM trigger");
+MODULE_LICENSE("GPL");