[PATCH v5 4/8] bus: add driver for the Technologic Systems NBUS

Sebastien Bourdelin
2017-07-14T20:33:36Z

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 v4 -> v5:
- fix missing signed off

Changes v3 -> v4:
- rebase on master
- fix vendor prefixes for dts properties (suggested by Rob Herring)
- v3 was acked by Linus Walleij

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 2408ea38a39c..3465e0decac5 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -157,6 +157,14 @@ 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..073fd9011154
--- /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 */
--
2.13.0