[PATCH v3 4/6] bus: add driver for the Technologic Systems NBUS

[Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>]

This driver implements a GPIOs bit-banged bus, called the NBUS by
Technologic Systems. It is used to communicate with the peripherals in
the FPGA on the TS-4600 SoM.

Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
---
Changes v2 -> v3:
  - rebase on master
  - remove all call to the "inline" keyword in functions to let the
  compiler decide when required (suggested by Linus Walleij)
  - move the struct ts_nbus to the driver code instead of its header
  file (suggested by Linus Walleij)
  - use the bitops header and the BIT macro (suggested by Linus Walleij)
  - move the mutex to the struct ts_nbus instead to have it statically
  declared in the driver code (suggested by Linus Walleij)
  - remove the ts_nbus_set_mode function to simplify the logic
  (suggested by Linus Walleij)
  - the nbus will always need 8 data lines, remove the use of the
  ndescs when dealing with the data gpios and hardcode the value for
  simplicity instead (suggested by Linus Walleij)
  - add more comments (suggested by Linus Walleij)
  - rework all the ts_nbus_read_... functions to propagate the
  gpiod_get_value_... errno code (suggested by Linus Walleij)
  - few typos and code reformating for lisibility

Changes v1 -> v2:
  - rebase on master
  - the driver now populate its child nodes
  - remove the 'default y' option from the Kconfig
  - rework the driver to not use singleton anymore (suggested by Linus
  Walleij)
  - replace the use of the legacy GPIO API with gpiod (suggested by
  Linus Walleij)
  - use the ts vendor prefix for gpios (suggested by Rob Herring)
---
 drivers/bus/Kconfig     |   8 ++
 drivers/bus/Makefile    |   1 +
 drivers/bus/ts-nbus.c   | 375 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/ts-nbus.h |  18 +++
 4 files changed, 402 insertions(+)
 create mode 100644 drivers/bus/ts-nbus.c
 create mode 100644 include/linux/ts-nbus.h

diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index 0a52da439abf..a9998081b01e 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -158,6 +158,14 @@ config TEGRA_GMI
 	  Driver for the Tegra Generic Memory Interface bus which can be used
 	  to attach devices such as NOR, UART, FPGA and more.
 
+config TS_NBUS
+	tristate "Technologic Systems NBUS Driver"
+	depends on SOC_IMX28
+	depends on OF_GPIO && PWM
+	help
+	  Driver for the Technologic Systems NBUS which is used to interface
+	  with the peripherals in the FPGA of the TS-4600 SoM.
+
 config UNIPHIER_SYSTEM_BUS
 	tristate "UniPhier System Bus driver"
 	depends on ARCH_UNIPHIER && OF
diff --git a/drivers/bus/Makefile b/drivers/bus/Makefile
index cc6364bec054..72377f77651c 100644
--- a/drivers/bus/Makefile
+++ b/drivers/bus/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_SIMPLE_PM_BUS)	+= simple-pm-bus.o
 obj-$(CONFIG_TEGRA_ACONNECT)	+= tegra-aconnect.o
 obj-$(CONFIG_TEGRA_GMI)		+= tegra-gmi.o
+obj-$(CONFIG_TS_NBUS)		+= ts-nbus.o
 obj-$(CONFIG_UNIPHIER_SYSTEM_BUS)	+= uniphier-system-bus.o
 obj-$(CONFIG_VEXPRESS_CONFIG)	+= vexpress-config.o
 
diff --git a/drivers/bus/ts-nbus.c b/drivers/bus/ts-nbus.c
new file mode 100644
index 000000000000..25714421f911
--- /dev/null
+++ b/drivers/bus/ts-nbus.c
@@ -0,0 +1,375 @@
+/*
+ * NBUS driver for TS-4600 based boards
+ *
+ * Copyright (c) 2016 - Savoir-faire Linux
+ * Author: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ *
+ * This driver implements a GPIOs bit-banged bus, called the NBUS by Technologic
+ * Systems. It is used to communicate with the peripherals in the FPGA on the
+ * TS-4600 SoM.
+ */
+
+#include <linux/bitops.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/ts-nbus.h>
+
+#define TS_NBUS_DIRECTION_IN  0
+#define TS_NBUS_DIRECTION_OUT 1
+#define TS_NBUS_WRITE_ADR 0
+#define TS_NBUS_WRITE_VAL 1
+
+struct ts_nbus {
+	struct pwm_device *pwm;
+	struct gpio_descs *data;
+	struct gpio_desc *csn;
+	struct gpio_desc *txrx;
+	struct gpio_desc *strobe;
+	struct gpio_desc *ale;
+	struct gpio_desc *rdy;
+	struct mutex lock;
+};
+
+/*
+ * request all gpios required by the bus.
+ */
+static int ts_nbus_init_pdata(struct platform_device *pdev, struct ts_nbus
+		*ts_nbus)
+{
+	ts_nbus->data = devm_gpiod_get_array(&pdev->dev, "ts-data",
+			GPIOD_OUT_HIGH);
+	if (IS_ERR(ts_nbus->data)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-data-gpio from dts\n");
+		return PTR_ERR(ts_nbus->data);
+	}
+
+	ts_nbus->csn = devm_gpiod_get(&pdev->dev, "ts-csn", GPIOD_OUT_HIGH);
+	if (IS_ERR(ts_nbus->csn)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-csn-gpio from dts\n");
+		return PTR_ERR(ts_nbus->csn);
+	}
+
+	ts_nbus->txrx = devm_gpiod_get(&pdev->dev, "ts-txrx", GPIOD_OUT_HIGH);
+	if (IS_ERR(ts_nbus->txrx)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-txrx-gpio from dts\n");
+		return PTR_ERR(ts_nbus->txrx);
+	}
+
+	ts_nbus->strobe = devm_gpiod_get(&pdev->dev, "ts-strobe", GPIOD_OUT_HIGH);
+	if (IS_ERR(ts_nbus->strobe)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-strobe-gpio from dts\n");
+		return PTR_ERR(ts_nbus->strobe);
+	}
+
+	ts_nbus->ale = devm_gpiod_get(&pdev->dev, "ts-ale", GPIOD_OUT_HIGH);
+	if (IS_ERR(ts_nbus->ale)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-ale-gpio from dts\n");
+		return PTR_ERR(ts_nbus->ale);
+	}
+
+	ts_nbus->rdy = devm_gpiod_get(&pdev->dev, "ts-rdy", GPIOD_IN);
+	if (IS_ERR(ts_nbus->rdy)) {
+		dev_err(&pdev->dev, "failed to retrieve ts-rdy-gpio from dts\n");
+		return PTR_ERR(ts_nbus->rdy);
+	}
+
+	return 0;
+}
+
+/*
+ * the data gpios are used for reading and writing values, their directions
+ * should be adjusted accordingly.
+ */
+static void ts_nbus_set_direction(struct ts_nbus *ts_nbus, int direction)
+{
+	int i;
+
+	for (i = 0; i < 8; i++) {
+		if (direction == TS_NBUS_DIRECTION_IN)
+			gpiod_direction_input(ts_nbus->data->desc[i]);
+		else
+			/* when used as output the default state of the data
+			 * lines are set to high */
+			gpiod_direction_output(ts_nbus->data->desc[i], 1);
+	}
+}
+
+/*
+ * reset the bus in its initial state.
+ * The data, csn, strobe and ale lines must be zero'ed to let the FPGA knows a
+ * new transaction can be process.
+ */
+static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus)
+{
+	int i;
+	int values[8];
+
+	for (i = 0; i < 8; i++)
+		values[i] = 0;
+
+	gpiod_set_array_value_cansleep(8, ts_nbus->data->desc, values);
+	gpiod_set_value_cansleep(ts_nbus->csn, 0);
+	gpiod_set_value_cansleep(ts_nbus->strobe, 0);
+	gpiod_set_value_cansleep(ts_nbus->ale, 0);
+}
+
+/*
+ * let the FPGA knows it can process.
+ */
+static void ts_nbus_start_transaction(struct ts_nbus *ts_nbus)
+{
+	gpiod_set_value_cansleep(ts_nbus->strobe, 1);
+}
+
+/*
+ * read a byte value from the data gpios.
+ * return 0 on success or negative errno on failure.
+ */
+static int ts_nbus_read_byte(struct ts_nbus *ts_nbus, u8 *val)
+{
+	struct gpio_descs *gpios = ts_nbus->data;
+	int ret, i;
+
+	*val = 0;
+	for (i = 0; i < 8; i++) {
+		ret = gpiod_get_value_cansleep(gpios->desc[i]);
+		if (ret < 0)
+			return ret;
+		if (ret)
+			*val |= BIT(i);
+	}
+
+	return 0;
+}
+
+/*
+ * set the data gpios accordingly to the byte value.
+ */
+static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte)
+{
+	struct gpio_descs *gpios = ts_nbus->data;
+	int i;
+	int values[8];
+
+	for (i = 0; i < 8; i++)
+		if (byte & BIT(i))
+			values[i] = 1;
+		else
+			values[i] = 0;
+
+	gpiod_set_array_value_cansleep(8, gpios->desc, values);
+}
+
+/*
+ * reading the bus consists of resetting the bus, then notifying the FPGA to
+ * send the data in the data gpios and return the read value.
+ * return 0 on success or negative errno on failure.
+ */
+static int ts_nbus_read_bus(struct ts_nbus *ts_nbus, u8 *val)
+{
+	ts_nbus_reset_bus(ts_nbus);
+	ts_nbus_start_transaction(ts_nbus);
+
+	return ts_nbus_read_byte(ts_nbus, val);
+}
+
+/*
+ * writing to the bus consists of resetting the bus, then define the type of
+ * command (address/value), write the data and notify the FPGA to retrieve the
+ * value in the data gpios.
+ */
+static void ts_nbus_write_bus(struct ts_nbus *ts_nbus, int cmd, u8 val)
+{
+	ts_nbus_reset_bus(ts_nbus);
+
+	if (cmd == TS_NBUS_WRITE_ADR)
+		gpiod_set_value_cansleep(ts_nbus->ale, 1);
+
+	ts_nbus_write_byte(ts_nbus, val);
+	ts_nbus_start_transaction(ts_nbus);
+}
+
+/*
+ * read the value in the FPGA register at the given address.
+ * return 0 on success or negative errno on failure.
+ */
+int ts_nbus_read(struct ts_nbus *ts_nbus, u8 adr, u16 *val)
+{
+	int ret, i;
+	u8 byte;
+
+	/* bus access must be atomic */
+	mutex_lock(&ts_nbus->lock);
+
+	/* set the bus in read mode */
+	gpiod_set_value_cansleep(ts_nbus->txrx, 0);
+
+	/* write address */
+	ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);
+
+	/* set the data gpios direction as input before reading */
+	ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_IN);
+
+	/* reading value MSB first */
+	do {
+		*val = 0;
+		byte = 0;
+		for (i = 1; i >= 0; i--) {
+			/* read a byte from the bus, leave on error */
+			ret = ts_nbus_read_bus(ts_nbus, &byte);
+			if (ret < 0)
+				goto err;
+
+			/* append the byte read to the final value */
+			*val |= byte << (i * 8);
+		}
+		gpiod_set_value_cansleep(ts_nbus->csn, 1);
+		ret = gpiod_get_value_cansleep(ts_nbus->rdy);
+	} while (ret);
+
+err:
+	/* restore the data gpios direction as output after reading */
+	ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_OUT);
+
+	mutex_unlock(&ts_nbus->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ts_nbus_read);
+
+/*
+ * write the desired value in the FPGA register at the given address.
+ */
+int ts_nbus_write(struct ts_nbus *ts_nbus, u8 adr, u16 val)
+{
+	int i;
+
+	/* bus access must be atomic */
+	mutex_lock(&ts_nbus->lock);
+
+	/* set the bus in write mode */
+	gpiod_set_value_cansleep(ts_nbus->txrx, 1);
+
+	/* write address */
+	ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);
+
+	/* writing value MSB first */
+	for (i = 1; i >= 0; i--)
+		ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_VAL, (u8)(val >> (i * 8)));
+
+	/* wait for completion */
+	gpiod_set_value_cansleep(ts_nbus->csn, 1);
+	while (gpiod_get_value_cansleep(ts_nbus->rdy) != 0) {
+		gpiod_set_value_cansleep(ts_nbus->csn, 0);
+		gpiod_set_value_cansleep(ts_nbus->csn, 1);
+	}
+
+	mutex_unlock(&ts_nbus->lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ts_nbus_write);
+
+static int ts_nbus_probe(struct platform_device *pdev)
+{
+	struct pwm_device *pwm;
+	struct pwm_args pargs;
+	struct device *dev = &pdev->dev;
+	struct ts_nbus *ts_nbus;
+	int ret;
+
+	ts_nbus = devm_kzalloc(dev, sizeof(*ts_nbus), GFP_KERNEL);
+	if (!ts_nbus)
+		return -ENOMEM;
+
+	mutex_init(&ts_nbus->lock);
+
+	ret = ts_nbus_init_pdata(pdev, ts_nbus);
+	if (ret < 0)
+		return ret;
+
+	pwm = devm_pwm_get(dev, NULL);
+	if (IS_ERR(pwm)) {
+		ret = PTR_ERR(pwm);
+		if (ret != -EPROBE_DEFER)
+			dev_err(dev, "unable to request PWM\n");
+		return ret;
+	}
+
+	pwm_get_args(pwm, &pargs);
+	if (!pargs.period) {
+		dev_err(&pdev->dev, "invalid PWM period\n");
+		return -EINVAL;
+	}
+
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(pwm);
+	ret = pwm_config(pwm, pargs.period, pargs.period);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * we can now start the FPGA and populate the peripherals.
+	 */
+	pwm_enable(pwm);
+	ts_nbus->pwm = pwm;
+
+	/*
+	 * let the child nodes retrieve this instance of the ts-nbus.
+	 */
+	dev_set_drvdata(dev, ts_nbus);
+
+	ret = of_platform_populate(dev->of_node, NULL, NULL, dev);
+	if (ret < 0)
+		return ret;
+
+	dev_info(dev, "initialized\n");
+
+	return 0;
+}
+
+static int ts_nbus_remove(struct platform_device *pdev)
+{
+	struct ts_nbus *ts_nbus = dev_get_drvdata(&pdev->dev);
+
+	/* shutdown the FPGA */
+	mutex_lock(&ts_nbus->lock);
+	pwm_disable(ts_nbus->pwm);
+	mutex_unlock(&ts_nbus->lock);
+
+	return 0;
+}
+
+static const struct of_device_id ts_nbus_of_match[] = {
+	{ .compatible = "technologic,ts-nbus", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ts_nbus_of_match);
+
+static struct platform_driver ts_nbus_driver = {
+	.probe		= ts_nbus_probe,
+	.remove		= ts_nbus_remove,
+	.driver		= {
+		.name	= "ts_nbus",
+		.of_match_table = ts_nbus_of_match,
+	},
+};
+
+module_platform_driver(ts_nbus_driver);
+
+MODULE_ALIAS("platform:ts_nbus");
+MODULE_AUTHOR("Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>");
+MODULE_DESCRIPTION("Technologic Systems NBUS");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/ts-nbus.h b/include/linux/ts-nbus.h
new file mode 100644
index 000000000000..5bd4c822f7cf
--- /dev/null
+++ b/include/linux/ts-nbus.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2016 - Savoir-faire Linux
+ * Author: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#ifndef _TS_NBUS_H
+#define _TS_NBUS_H
+
+struct ts_nbus;
+
+extern int ts_nbus_read(struct ts_nbus *ts_nbus, u8 adr, u16 *val);
+extern int ts_nbus_write(struct ts_nbus *ts_nbus, u8 adr, u16 val);
+
+#endif /* _TS_NBUS_H */
-- 
2.12.0