[PATCH v3] USB: serial: ftdi_sio: implement GPIO support for FT-X devices

[Karoly Pados]

This patch allows using the CBUS pins of FT-X devices as GPIO in CBUS
bitbanging mode. There is no conflict between the GPIO and VCP
functionality in this mode. Tested on FT230X and FT231X.

As there is no way to request the current CBUS register configuration
from the device, all CBUS pins are set to a known state when the first
GPIO is requested. This allows using libftdi to set the GPIO pins
before loading this module for UART functionality, a behavior that
existing applications might be relying upon (though no specific case
is known to the authors of this patch).

Signed-off-by: Karoly Pados <pados@xxxxxxxx>
---

Changelog:
- v2: Fix compile error when CONFIG_GPIOLIB is not defined.
- v3: Incorporate review feedback.

Though there is no code copied, libftdi was used as 
a reference. ftdi_read_eeprom is based on Loic Poulain's patch.

I've removed --strict from checkpatch.pl invocation, yet it still gives
me those warnings it shouldn't. Maybe I have a different version? Now
in v3 I also get two new I'm not sure how to deal with. Rest of text 
below same as before.

I noticed there have been numerous historic attempts by other people at 
adding GPIO support to ftdi_sio. One tried adding it in some very 
application-specific way, another one tried to use the mfd framework, the
tried using a GPIO mode which is mutually exclusive to VCP, another
one did not implement the review results etc... I hope I learned from those 
attempts and am planning to respond to reviews. Also, this patch follows 
the rough structure of the GPIO support for cp210x devices that have 
already been accepted, in the hope that it is a good starting point.

This patch uses CBUS bitbanging mode, which works nicely in parallel with
the VCP function. The other modes do not, and so IMHO it does not make
sense to try adding them to this same module.

For this device, whenever changing the state of any single pin, all the
others need to be written too. This means in order to change any pin, we 
need to know the current state of all the others. So when using GPIO,
we need to have a known starting state for all pins, but there seems to 
be no way to retrieve the existing GPIO configuration (directions and
output register values). The way I handle this in this patch is that when
requesting a GPIO for the first time, the module initializes all pins to 
a known default state (to inputs). Input was chosen, because a potentially
floating pin is better than a potential driver conflict, because the latter
could result in hardware damage. However, if the user does not request a 
GPIO, the CBUS pins are not initialized, avoiding unnecessarily changing 
hardware state. I figured I cannot rely on the default power-on state of
the device for this as the user might have used libftdi before loading 
our module. When the module is unloaded, CBUS bitbanging mode is exited 
if it were us who entered it earlier.


 drivers/usb/serial/ftdi_sio.c | 318 +++++++++++++++++++++++++++++++++-
 drivers/usb/serial/ftdi_sio.h |  27 ++-
 2 files changed, 343 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index b5cef322826f..00b6c6abdd09 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -40,6 +40,9 @@
 #include <linux/usb.h>
 #include <linux/serial.h>
 #include <linux/usb/serial.h>
+#if defined(CONFIG_GPIOLIB)
+#include <linux/gpio/driver.h>
+#endif
 #include "ftdi_sio.h"
 #include "ftdi_sio_ids.h"
 
@@ -72,6 +75,14 @@ struct ftdi_private {
 	unsigned int latency;		/* latency setting in use */
 	unsigned short max_packet_size;
 	struct mutex cfg_lock; /* Avoid mess by parallel calls of config ioctl() and change_speed() */
+#if defined(CONFIG_GPIOLIB)
+	struct gpio_chip gc;
+	bool	gpio_registered;  /* is the gpiochip in kernel registered */
+	bool	gpio_used;	  /* true if the user requested a gpio */
+	u8	gpio_altfunc;	  /* which pins are in gpio mode */
+	u8	gpio_input;	  /* pin directions cache */
+	u8	gpio_value;	  /* pin value for outputs */
+#endif
 };
 
 /* struct ftdi_sio_quirk is used by devices requiring special attention. */
@@ -1766,6 +1777,301 @@ static void remove_sysfs_attrs(struct usb_serial_port *port)
 
 }
 
+#if defined(CONFIG_GPIOLIB)
+
+static int ftdi_set_bitmode_req(struct usb_serial_port *port, u8 mode)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	int result;
+	u16 val;
+
+	/* device's direction polarity is different from kernel's */
+	u8 direction = (~priv->gpio_input) & 0x0f;
+
+	val = (mode << 8) | (direction << 4) | (priv->gpio_value & 0x0f);
+	result = usb_control_msg(serial->dev,
+				 usb_sndctrlpipe(serial->dev, 0),
+				 FTDI_SIO_SET_BITMODE_REQUEST,
+				 FTDI_SIO_SET_BITMODE_REQUEST_TYPE, val,
+				 priv->interface, NULL, 0, WDR_TIMEOUT);
+
+	if (result < 0) {
+		dev_err(&serial->interface->dev,
+			"bitmode request failed for value: %d\n",
+			val);
+	}
+
+	return result;
+}
+
+static int ftdi_set_cbus_pins(struct usb_serial_port *port)
+{
+	return ftdi_set_bitmode_req(port, FTDI_SIO_BITMODE_CBUS);
+}
+
+static int ftdi_exit_cbus_mode(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	priv->gpio_input = 0;
+	priv->gpio_value = 0;
+	return ftdi_set_bitmode_req(port, FTDI_SIO_BITMODE_RESET);
+}
+
+static int ftdi_gpio_request(struct gpio_chip *gc, unsigned int offset)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	int result;
+
+	if (priv->gpio_altfunc & BIT(offset))
+		return -ENODEV;
+
+	if (!priv->gpio_used) {
+		/* Set default pin states, as we cannot get them from device */
+		priv->gpio_input = 0xff;
+		priv->gpio_value = 0x00;
+		result = ftdi_set_cbus_pins(port);
+		if (result)
+			return result;
+
+		priv->gpio_used = true;
+	}
+
+	return 0;
+}
+
+static int ftdi_gpio_get(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	unsigned char *rcvbuf;
+	int result;
+
+	rcvbuf = kmalloc(1, GFP_KERNEL);
+	if (!rcvbuf)
+		return -ENOMEM;
+
+	result = usb_control_msg(serial->dev,
+				 usb_rcvctrlpipe(serial->dev, 0),
+				 FTDI_SIO_READ_PINS_REQUEST,
+				 FTDI_SIO_READ_PINS_REQUEST_TYPE, 0,
+				 priv->interface, rcvbuf, 1, WDR_TIMEOUT);
+	if (result < 0) {
+	} else if (result < 1)
+		result = -EIO;
+	else
+		result = !!(rcvbuf[0] & BIT(gpio));
+
+	kfree(rcvbuf);
+
+	return result;
+}
+
+static void ftdi_gpio_set(struct gpio_chip *gc,
+			      unsigned int gpio,
+			      int value)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	int result;
+
+	if (value)
+		priv->gpio_value |= BIT(gpio);
+	else
+		priv->gpio_value &= ~BIT(gpio);
+
+	result = ftdi_set_cbus_pins(port);
+	if (result < 0) {
+		dev_err(&port->serial->interface->dev,
+			"failed to set GPIO value: %d\n",
+			result);
+	}
+}
+
+static int ftdi_gpio_direction_get(struct gpio_chip *gc,
+				       unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	return priv->gpio_input & BIT(gpio);
+}
+
+static int ftdi_gpio_direction_input(struct gpio_chip *gc,
+					 unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	priv->gpio_input |= BIT(gpio);
+
+	return ftdi_set_cbus_pins(port);
+}
+
+static int ftdi_gpio_direction_output(struct gpio_chip *gc,
+					  unsigned int gpio,
+					  int value)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	priv->gpio_input &= ~BIT(gpio);
+	if (value)
+		priv->gpio_value |= BIT(gpio);
+	else
+		priv->gpio_value &= ~BIT(gpio);
+
+	return ftdi_set_cbus_pins(port);
+}
+
+/* Returns the number of bytes read */
+static int ftdi_read_eeprom(struct usb_serial *serial,
+			    void *dst,	/* must be kmalloc'd using GFP_KERNEL*/
+			    u16 addr,	/* must be aligned to 16 bits */
+			    u16 nbytes)	/* must be a multiple of 16 bits */
+{
+	int read = 0;
+
+	/* Argument checks */
+	if (addr % 2 != 0)
+		return -EINVAL;
+	if (nbytes % 2 != 0)
+		return -EINVAL;
+
+	/* Read EEPROM two bytes at a time */
+	while (read < nbytes) {
+		int rv;
+
+		rv = usb_control_msg(serial->dev,
+				     usb_rcvctrlpipe(serial->dev, 0),
+				     FTDI_SIO_READ_EEPROM_REQUEST,
+				     FTDI_SIO_READ_EEPROM_REQUEST_TYPE,
+				     0, (addr + read) / 2, dst + read, 2,
+				     WDR_TIMEOUT);
+		if (rv < 0)
+			return rv;
+
+		read += rv;
+
+		if (rv < 2)
+			break;
+	}
+
+	return read;
+}
+
+static int ftx_gpioconf_init(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	const u16 cbus_cfg_addr = 0x1a;
+	const u16 cbus_cfg_size = 8;
+	u8 *cbus_cfg_buf;
+	int result;
+	u8 i;
+
+	/* Read a part of device EEPROM */
+	cbus_cfg_buf = kmalloc(cbus_cfg_size, GFP_KERNEL);
+	if (!cbus_cfg_buf)
+		return -ENOMEM;
+
+	result = ftdi_read_eeprom(serial, cbus_cfg_buf,
+				  cbus_cfg_addr, cbus_cfg_size);
+
+	if (result < 0)
+		goto out_free;
+	else if (result < 8) {
+		result = -EIO;
+		goto out_free;
+	} else
+		result = 0;
+
+	/* Chip-type guessing logic based on libftdi. */
+	priv->gc.ngpio = 4;  /* FT230X, FT231X */
+	if (le16_to_cpu(serial->dev->descriptor.bcdDevice) != 0x1000)
+		priv->gc.ngpio = 1;  /* FT234XD */
+
+	/* Determine which pins are configured for CBUS bitbanging */
+	priv->gpio_altfunc = 0xff;
+	for (i = 0; i < priv->gc.ngpio; ++i) {
+		if (cbus_cfg_buf[i] == FTDI_SIO_CBUS_MUX_GPIO)
+			priv->gpio_altfunc &= ~BIT(i);
+	}
+
+out_free:
+	kfree(cbus_cfg_buf);
+
+	return result;
+}
+
+static int ftdi_gpio_init(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	int result;
+
+	/* Device-specific initializations */
+	switch (priv->chip_type) {
+	case FTX:
+		result = ftx_gpioconf_init(port);
+		break;
+	default:
+		return 0;
+	}
+
+	if (result < 0)
+		return result;
+
+	/* Register GPIO chip to kernel */
+	priv->gc.label = "ftdi-cbus";
+	priv->gc.request = ftdi_gpio_request;
+	priv->gc.get_direction = ftdi_gpio_direction_get;
+	priv->gc.direction_input = ftdi_gpio_direction_input;
+	priv->gc.direction_output = ftdi_gpio_direction_output;
+	priv->gc.get = ftdi_gpio_get;
+	priv->gc.set = ftdi_gpio_set;
+	priv->gc.owner = THIS_MODULE;
+	priv->gc.parent = &serial->interface->dev;
+	priv->gc.base = -1;
+	priv->gc.can_sleep = true;
+
+	result = gpiochip_add_data(&priv->gc, port);
+	if (!result)
+		priv->gpio_registered = true;
+
+	return result;
+}
+
+static void ftdi_gpio_remove(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	if (priv->gpio_used) {
+		/* Remark: Exiting CBUS-mode does not reset pin states too */
+		ftdi_exit_cbus_mode(port);
+		priv->gpio_used = false;
+	}
+
+	if (priv->gpio_registered) {
+		gpiochip_remove(&priv->gc);
+		priv->gpio_registered = false;
+	}
+}
+
+#else
+
+static int ftdi_gpio_init(struct usb_serial_port *port)
+{
+	return 0;
+}
+
+static void ftdi_gpio_remove(struct usb_serial_port *port) { }
+
+#endif
+
 /*
  * ***************************************************************************
  * FTDI driver specific functions
@@ -1794,7 +2100,7 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv;
 	const struct ftdi_sio_quirk *quirk = usb_get_serial_data(port->serial);
-
+	int result;
 
 	priv = kzalloc(sizeof(struct ftdi_private), GFP_KERNEL);
 	if (!priv)
@@ -1813,6 +2119,14 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 		priv->latency = 16;
 	write_latency_timer(port);
 	create_sysfs_attrs(port);
+
+	result = ftdi_gpio_init(port);
+	if (result < 0) {
+		dev_err(&port->serial->interface->dev,
+			"GPIO initialisation failed: %d\n",
+			result);
+	}
+
 	return 0;
 }
 
@@ -1930,6 +2244,8 @@ static int ftdi_sio_port_remove(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 
+	ftdi_gpio_remove(port);
+
 	remove_sysfs_attrs(port);
 
 	kfree(priv);
diff --git a/drivers/usb/serial/ftdi_sio.h b/drivers/usb/serial/ftdi_sio.h
index dcd0b6e05baf..5a296e9e87a2 100644
--- a/drivers/usb/serial/ftdi_sio.h
+++ b/drivers/usb/serial/ftdi_sio.h
@@ -35,7 +35,10 @@
 #define FTDI_SIO_SET_EVENT_CHAR		6 /* Set the event character */
 #define FTDI_SIO_SET_ERROR_CHAR		7 /* Set the error character */
 #define FTDI_SIO_SET_LATENCY_TIMER	9 /* Set the latency timer */
-#define FTDI_SIO_GET_LATENCY_TIMER	10 /* Get the latency timer */
+#define FTDI_SIO_GET_LATENCY_TIMER	0x0a /* Get the latency timer */
+#define FTDI_SIO_SET_BITMODE		0x0b /* Set CBUS GPIO pin mode */
+#define FTDI_SIO_READ_PINS		0x0c /* Read immediate value of pins */
+#define FTDI_SIO_READ_EEPROM		0x90 /* Read EEPROM */
 
 /* Interface indices for FT2232, FT2232H and FT4232H devices */
 #define INTERFACE_A		1
@@ -433,6 +436,28 @@ enum ftdi_sio_baudrate {
  *         1 = active
  */
 
+/* FTDI_SIO_SET_BITMODE */
+#define FTDI_SIO_SET_BITMODE_REQUEST_TYPE 0x40
+#define FTDI_SIO_SET_BITMODE_REQUEST FTDI_SIO_SET_BITMODE
+
+/* Possible bitmodes for FTDI_SIO_SET_BITMODE_REQUEST */
+#define FTDI_SIO_BITMODE_RESET		0x00
+#define FTDI_SIO_BITMODE_CBUS		0x20
+
+/* FTDI_SIO_READ_PINS */
+#define FTDI_SIO_READ_PINS_REQUEST_TYPE 0xc0
+#define FTDI_SIO_READ_PINS_REQUEST FTDI_SIO_READ_PINS
+
+/*
+ * FTDI_SIO_READ_EEPROM
+ *
+ * EEPROM format found in FTDI AN_201, "FT-X MTP memory Configuration",
+ * http://www.ftdichip.com/Support/Documents/AppNotes/AN_201_FT-X%20MTP%20Memory%20Configuration.pdf
+ */
+#define FTDI_SIO_READ_EEPROM_REQUEST_TYPE 0xc0
+#define FTDI_SIO_READ_EEPROM_REQUEST FTDI_SIO_READ_EEPROM
+
+#define FTDI_SIO_CBUS_MUX_GPIO		8
 
 
 /* Descriptors returned by the device
-- 
2.18.0