[PATCH v3 08/16] HID: ft260: uart: add modem pins control via ioctl

[Michael Zaidman <michael.zaidman@gmail.com>]

Add TIOCMGET/TIOCMSET (and thus TIOCMBIS/TIOCMBIC) support so userspace
can drive DTR/RTS when the modem pins are in GPIO mode. This enables
programming an ESP32 over the FT260 with esptool, which resets the chip
via those lines.

Set up the gpiochip and the sysfs attributes on the UART interface when
the chip mode has UART, and on the I2C interface only in the I2C-only
mode. Before, the choice depended on USB interface number 0, which is
the I2C interface in mode 3, but TIOCMGET and TIOCMSET run on the UART
interface and need the GPIO state there. Add DCD and RI (GPIO4 and
GPIO5) to the GPIO set of UART modes 3 and 4, so the mask that TIOCMGET
and TIOCMSET check covers the two lines that TIOCMGET reports.

The RTS, CTS, DTR and DSR pins are active-low, so TIOCMGET inverts the
sense of those four lines and TIOCMSET drives 0 to assert them. DCD and
RI are not inverted. Rio Liu found and fixed the polarity.

Keep the errno from ft260_get_interface_type(), so that a failed
status read does not let probe succeed after the teardown.

TIOCMGET and TIOCMSET work only while the modem pins are GPIOs, and
return -EINVAL otherwise. They check gpio_en under port->lock, so that
a termios or sysfs change cannot switch the pins to flow control
between the check and the GPIO report. TIOCMGET returns the error of
the GPIO read. TIOCMSET builds its report from the cached GPIO state,
which it copies under the same lock.

The tty hangup does not wait for a TIOCMGET or TIOCMSET that already
runs, because the tty core handles them without a line discipline
reference. ft260_remove() sets a flag under port->lock after the
hangup, so it waits for such a call, and a later one returns -ENODEV
instead of using hdev after hid_hw_stop().

Co-developed-by: Rio Liu <rio@r26.me>
Signed-off-by: Rio Liu <rio@r26.me>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>

---
v2:
Polarity fix folded in (Rio Liu).

Fixes for the issues reported by Sashiko:
- The errno of ft260_get_interface_type() is kept, so probe does not
  succeed after the teardown.
- TIOCMGET and TIOCMSET return -EINVAL when the modem pins are not
  GPIOs, and TIOCMGET returns the error of the GPIO read.
- TIOCMSET copies the cached GPIO state under port->lock.

v3:
Fixes for the issues reported by Sashiko:
- gpio_en checked under port->lock in tiocmget() and tiocmset(), so a
  termios or sysfs change cannot switch the pins between the check and
  the GPIO report.
- tiocmget() and tiocmset() return -ENODEV after ft260_remove(), so
  they do not use hdev after hid_hw_stop().
- tiocmget() cannot run before dev->gc is set, because
  ft260_uart_probe() registers the TTY last since patch 2.
---
 drivers/hid/hid-ft260.c | 168 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 151 insertions(+), 17 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 75ba68e2e8fc..d795355fc26b 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -16,6 +16,7 @@
 #include <linux/serial.h>
 #include <linux/serial_core.h>
 #include <linux/kfifo.h>
+#include <linux/tty.h>
 #include <linux/tty_flip.h>
 #include <linux/math.h>
 #include <linux/minmax.h>
@@ -183,7 +184,7 @@ enum {
 	FT260_GPIO_DIR_OUTPUT		= 0x01,
 };
 
-/* GPIO offsets */
+/* GPIO bit masks */
 #define FT260_GPIO_0		BIT(0)
 #define FT260_GPIO_1		BIT(1)
 #define FT260_GPIO_2		BIT(2)
@@ -213,7 +214,8 @@ enum {
 #define FT260_GPIO_UART_MODE_1_SET	FT260_GPIO_UART_DTR_DSR
 #define FT260_GPIO_UART_MODE_2_SET	FT260_GPIO_UART_RTS_CTS
 #define FT260_GPIO_UART_MODE_3_SET	(FT260_GPIO_UART_RTS_CTS | \
-					 FT260_GPIO_UART_DTR_DSR)
+					 FT260_GPIO_UART_DTR_DSR | \
+					 FT260_GPIO_UART_DCD_RI)
 #define FT260_GPIO_UART_MODE_4_SET	FT260_GPIO_UART_MODE_3_SET
 #define FT260_GPIO_UART_DEFAULT		FT260_GPIO_UART_MODE_0_SET
 #define FT260_GPIO_UART_MODE_1_CLR	(FT260_GPIO_UART_RX_TX | \
@@ -223,6 +225,16 @@ enum {
 #define FT260_GPIO_UART_MODE_3_CLR	FT260_GPIO_UART_RX_TX
 #define FT260_GPIO_UART_MODES		5
 
+/* UART modem control GPIO offsets */
+enum {
+	FT260_GPIO_UART_DCD		= (4),
+	FT260_GPIO_UART_RI		= (5),
+	FT260_GPIO_UART_RTS		= (7),
+	FT260_GPIO_UART_CTS		= (10),
+	FT260_GPIO_UART_DTR		= (11),
+	FT260_GPIO_UART_DSR		= (13),
+};
+
 #define FT260_SET_REQUEST_VALUE(report_id) ((FT260_FEATURE << 8) | (report_id))
 
 /* Feature In reports */
@@ -449,6 +461,7 @@ MODULE_DEVICE_TABLE(hid, ft260_devices);
 struct ft260_device {
 	struct i2c_adapter adap;
 	struct hid_device *hdev;
+	int chip_mode;
 	int iface_type;
 	int iface_id;
 	struct list_head device_list;
@@ -480,6 +493,8 @@ struct ft260_device {
 	struct ft260_gpio_state gpio;
 	u16 gpio_uart_mode[FT260_GPIO_UART_MODES];
 	bool uart_dcd_ri;
+	/* Set under lock by ft260_remove(); tiocm calls then stop */
+	bool removed;
 };
 
 static int ft260_hid_feature_report_get(struct hid_device *hdev,
@@ -1111,8 +1126,27 @@ static void ft260_gpio_en_update(struct hid_device *hdev, u8 req, u8 value)
 	else
 		ft260_gpio_en_clr(dev, bitmap);
 exit:
-	ft260_dbg("%s: enabled GPIOs: %04x\n", dev_name(&hdev->dev),
-		  dev->gpio_en);
+	ft260_dbg("%s: enabled GPIOs: %04x, bitmap %04x\n",
+		  dev_name(&hdev->dev), dev->gpio_en, bitmap);
+}
+
+static void ft260_gpio_output_cfg(struct ft260_gpio_state *gpio,
+				  u32 offset, int value)
+{
+	if (offset < FT260_GPIO_0_5_COUNT) {
+		gpio->dirs |= BIT(offset);
+		if (value)
+			gpio->vals |= !!value << offset;
+		else
+			gpio->vals &= ~BIT(offset);
+	} else {
+		offset = offset - FT260_GPIO_0_5_COUNT;
+		gpio->ex_dirs |= BIT(offset);
+		if (value)
+			gpio->ex_vals |= !!value << offset;
+		else
+			gpio->ex_vals &= ~BIT(offset);
+	}
 }
 
 static int ft260_gpio_set(struct gpio_chip *gc, u32 offset, int value)
@@ -1161,7 +1195,7 @@ static int ft260_gpio_set(struct gpio_chip *gc, u32 offset, int value)
 			rep.gpio.ex_vals &= ~BIT(offset);
 	}
 
-	ft260_dbg("dirs %#02x vals %#02x ex_dir %#02x ex_vals %#02x\n",
+	ft260_dbg("dirs %#02x vals %#02x ex_dirs %#02x ex_vals %#02x\n",
 		  rep.gpio.dirs, rep.gpio.vals,
 		  rep.gpio.ex_dirs, rep.gpio.ex_vals);
 
@@ -1419,6 +1453,7 @@ static int ft260_get_interface_type(struct ft260_device *dev,
 	ft260_dbg("wakeup_int: 0x%02x\n", cfg->enable_wakeup_int);
 
 	dev->power_saving_en = cfg->power_saving_en;
+	dev->chip_mode = cfg->chip_mode;
 
 	switch (cfg->chip_mode) {
 	case FT260_MODE_ALL:
@@ -1439,7 +1474,6 @@ static int ft260_get_interface_type(struct ft260_device *dev,
 		return -ENODEV;
 	}
 
-	dev->iface_type = ret;
 	return ret;
 }
 
@@ -1947,6 +1981,91 @@ static void ft260_uart_set_termios(struct tty_struct *tty,
 	ft260_uart_change_speed(port, &tty->termios, NULL);
 }
 
+static int ft260_uart_tiocmget(struct tty_struct *tty)
+{
+	struct ft260_device *port = tty->driver_data;
+	int gpios;
+
+	/*
+	 * The modem lines control via ioctl is allowed only
+	 * when the related pins are in the gpio mode.
+	 */
+	int mask = FT260_GPIO_UART_MODE_4_SET;
+
+	mutex_lock(&port->lock);
+	if (port->removed) {
+		mutex_unlock(&port->lock);
+		return -ENODEV;
+	}
+	if ((port->gpio_en & mask) != mask) {
+		ft260_dbg("Illegal gpio config %#02x != mask %#04x\n",
+			  port->gpio_en, mask);
+		mutex_unlock(&port->lock);
+		return -EINVAL;
+	}
+
+	gpios = ft260_gpio_get_all(&port->gc, FT260_GPIO_VALUE);
+	mutex_unlock(&port->lock);
+	if (gpios < 0)
+		return gpios;
+
+	return ((!(gpios & FT260_GPIO_B) ? TIOCM_RTS : 0) |
+		(!(gpios & FT260_GPIO_E) ? TIOCM_CTS : 0) |
+		(!(gpios & FT260_GPIO_F) ? TIOCM_DTR : 0) |
+		(!(gpios & FT260_GPIO_H) ? TIOCM_DSR : 0) |
+		((gpios & FT260_GPIO_4) ? TIOCM_CAR : 0) |
+		((gpios & FT260_GPIO_5) ? TIOCM_RNG : 0));
+}
+
+static int ft260_uart_tiocmset(struct tty_struct *tty,
+			       unsigned int set, unsigned int clear)
+{
+	int ret;
+	struct ft260_device *port = tty->driver_data;
+	struct ft260_gpio_write_request_report rep;
+	struct hid_device *hdev = port->hdev;
+	int mask = FT260_GPIO_UART_MODE_4_SET;
+
+	mutex_lock(&port->lock);
+	if (port->removed) {
+		mutex_unlock(&port->lock);
+		return -ENODEV;
+	}
+	if ((port->gpio_en & mask) != mask) {
+		ft260_dbg("Illegal gpio config %#02x != mask %#04x\n",
+			  port->gpio_en, mask);
+		mutex_unlock(&port->lock);
+		return -EINVAL;
+	}
+	rep.report = FT260_GPIO;
+	rep.gpio = port->gpio;
+
+	if (set & TIOCM_RTS)
+		ft260_gpio_output_cfg(&rep.gpio, FT260_GPIO_UART_RTS, 0);
+	if (set & TIOCM_DTR)
+		ft260_gpio_output_cfg(&rep.gpio, FT260_GPIO_UART_DTR, 0);
+	if (clear & TIOCM_RTS)
+		ft260_gpio_output_cfg(&rep.gpio, FT260_GPIO_UART_RTS, 1);
+	if (clear & TIOCM_DTR)
+		ft260_gpio_output_cfg(&rep.gpio, FT260_GPIO_UART_DTR, 1);
+
+	ft260_dbg("dirs %#02x vals %#02x ex_dirs %#02x ex_vals %#02x\n",
+		  rep.gpio.dirs, rep.gpio.vals,
+		  rep.gpio.ex_dirs, rep.gpio.ex_vals);
+
+	ret = ft260_hid_feature_report_set(hdev, (u8 *)&rep, sizeof(rep));
+	if (unlikely(ret < 0)) {
+		hid_err(hdev, "%s: cannot set GPIO: %d\n", __func__, ret);
+		mutex_unlock(&port->lock);
+		return -EIO;
+	}
+
+	port->gpio = rep.gpio;
+	mutex_unlock(&port->lock);
+
+	return 0;
+}
+
 static int ft260_uart_install(struct tty_driver *driver, struct tty_struct *tty)
 {
 	int idx = tty->index;
@@ -2027,6 +2146,8 @@ static const struct tty_operations ft260_uart_ops = {
 	.write_room		= ft260_uart_write_room,
 	.chars_in_buffer	= ft260_uart_chars_in_buffer,
 	.set_termios		= ft260_uart_set_termios,
+	.tiocmget		= ft260_uart_tiocmget,
+	.tiocmset		= ft260_uart_tiocmset,
 	.hangup			= ft260_uart_hangup,
 	.install		= ft260_uart_install,
 	.cleanup		= ft260_uart_cleanup,
@@ -2171,14 +2292,16 @@ static int ft260_i2c_probe(struct ft260_device *dev,
 		return ret;
 	}
 
-	ret = ft260_gpio_init(dev, cfg);
-	if (ret)
-		goto err_i2c_free;
+	if (cfg->chip_mode == FT260_MODE_I2C) {
+		ret = ft260_gpio_init(dev, cfg);
+		if (ret)
+			goto err_i2c_free;
 
-	ret = sysfs_create_group(&hdev->dev.kobj, &ft260_attr_group);
-	if (ret < 0) {
-		hid_err(hdev, "failed to create sysfs attrs\n");
-		goto err_gpio_remove;
+		ret = sysfs_create_group(&hdev->dev.kobj, &ft260_attr_group);
+		if (ret < 0) {
+			hid_err(hdev, "failed to create sysfs attrs\n");
+			goto err_gpio_remove;
+		}
 	}
 
 	return 0;
@@ -2231,7 +2354,8 @@ static int ft260_uart_probe(struct ft260_device *dev,
 
 	cfg->uart_mode = FT260_UART_CFG_FLOW_CTRL_NONE;
 
-	if (dev->iface_id == 0) {
+	if (dev->chip_mode & FT260_MODE_UART ||
+	    dev->chip_mode == FT260_MODE_ALL) {
 		ret = ft260_gpio_init(dev, cfg);
 		if (ret)
 			goto err_hid_report;
@@ -2326,8 +2450,9 @@ static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	ret = ft260_get_interface_type(dev, &cfg);
 	if (ret <= FT260_IFACE_NONE)
 		goto err_hid_close;
+	dev->iface_type = ret;
 
-	if (ret == FT260_IFACE_I2C) {
+	if (dev->iface_type == FT260_IFACE_I2C) {
 		ret = ft260_i2c_probe(dev, &cfg);
 		if (ret)
 			goto err_hid_close;
@@ -2366,10 +2491,19 @@ static void ft260_remove(struct hid_device *hdev)
 		tty_port_unregister_device(&dev->port, ft260_tty_driver,
 					   dev->index);
 		ft260_uart_port_remove(dev);
-		if (dev->iface_id == 0)
+		/*
+		 * The hangup does not wait for a TIOCMGET or TIOCMSET
+		 * that is running; they hold the lock while they use hdev.
+		 */
+		mutex_lock(&dev->lock);
+		dev->removed = true;
+		mutex_unlock(&dev->lock);
+		if (dev->chip_mode & FT260_MODE_UART ||
+		    dev->chip_mode == FT260_MODE_ALL)
 			sysfs_remove_group(&hdev->dev.kobj, &ft260_attr_group);
 	} else {
-		sysfs_remove_group(&hdev->dev.kobj, &ft260_attr_group);
+		if (dev->chip_mode == FT260_MODE_I2C)
+			sysfs_remove_group(&hdev->dev.kobj, &ft260_attr_group);
 		i2c_del_adapter(&dev->adap);
 	}
 
-- 
2.43.0