From e0b7be2ad39d65ddd59e65e654ce4196b8be69bc Mon Sep 17 00:00:00 2001
From: "Mychaela N. Falconia" <falcon@freecalypso.org>
Date: Fri, 2 Oct 2020 18:01:12 +0000
Subject: [PATCH 2/2] USB: serial: ftdi_sio: add support for FreeCalypso
 DUART28C adapter

FreeCalypso DUART28C is an FT2232D-based USB to dual UART adapter
with a special quirk: Channel B RTS and DTR outputs (BDBUS2 and BDBUS4
on the chip) have been repurposed to drive PWON and RESET controls
on Calypso targets.  The circuit is wired such that BDBUS[24] high
(RTS/DTR inactive) is the normal state with Iota VRPC controls
NOT activated, whereas BDBUS[24] low (RTS or DTR active) turn ON
the corresponding open drain control signal drivers.

A special ftdi_sio driver quirk is needed in order to suppress
automatic assertion of DTR & RTS on device open: this device's
special PWON and RESET control drivers MUST NOT be activated
when the port is ordinarily opened for plain serial communication,
instead they must only be activated when a special userspace
application explicitly requests such activation with a TIOCMBIS ioctl.
These special userspace applications are responsible for making the
needed pulse with a TIOCMBIS, delay, TIOCMBIC sequence.

The special quirk is conditionalized on the DUART28C adapter's custom
USB ID, and is further limited to FT2232D Channel B only: Channel A
is wired normally, with the chip's ADBUS2 and ADBUS4 outputs
actually being RTS and DTR rather than something else.

Signed-off-by: Mychaela N. Falconia <falcon@freecalypso.org>
---
 drivers/usb/serial/ftdi_sio.c     | 61 +++++++++++++++++++++++++++++++++++----
 drivers/usb/serial/ftdi_sio_ids.h |  1 +
 2 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 1587c22180c0..0ab2835d2c10 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -85,6 +85,8 @@ struct ftdi_private {
 				   this value */
 	int force_rtscts;	/* if non-zero, force RTS-CTS to always
 				   be enabled */
+	int no_auto_dtr_rts;	/* if non-zero, suppress automatic assertion
+				   of DTR & RTS on device open */
 
 	unsigned int latency;		/* latency setting in use */
 	unsigned short max_packet_size;
@@ -112,6 +114,7 @@ static int   ftdi_stmclite_probe(struct usb_serial *serial);
 static int   ftdi_8u2232c_probe(struct usb_serial *serial);
 static void  ftdi_USB_UIRT_setup(struct usb_serial_port *port);
 static void  ftdi_HE_TIRA1_setup(struct usb_serial_port *port);
+static void  ftdi_duart28c_setup(struct usb_serial_port *port);
 
 static const struct ftdi_quirk ftdi_jtag_quirk = {
 	.probe	= ftdi_jtag_probe,
@@ -137,6 +140,10 @@ static const struct ftdi_quirk ftdi_8u2232c_quirk = {
 	.probe	= ftdi_8u2232c_probe,
 };
 
+static const struct ftdi_quirk ftdi_duart28c_quirk = {
+	.port_probe = ftdi_duart28c_setup,
+};
+
 /*
  * The 8U232AM has the same API as the sio except for:
  * - it can support MUCH higher baudrates; up to:
@@ -1077,6 +1084,8 @@ static const struct usb_device_id id_table_combined[] = {
 		.driver_info = (kernel_ulong_t)&ftdi_jtag_quirk },
 	{ USB_DEVICE(FTDI_VID, FTDI_FALCONIA_JTAG_UNBUF_PID),
 		.driver_info = (kernel_ulong_t)&ftdi_jtag_quirk },
+	{ USB_DEVICE(FTDI_VID, FTDI_FALCONIA_DUART28C_PID),
+		.driver_info = (kernel_ulong_t)&ftdi_duart28c_quirk },
 	{ }					/* Terminating entry */
 };
 
@@ -2338,6 +2347,39 @@ static int ftdi_stmclite_probe(struct usb_serial *serial)
 	return 0;
 }
 
+/*
+ * FreeCalypso DUART28C is an FT2232D-based USB to dual UART adapter
+ * with a special quirk: Channel B RTS and DTR outputs (BDBUS2 and BDBUS4
+ * on the chip) have been repurposed to drive PWON and RESET controls
+ * on Calypso targets.  The circuit is wired such that BDBUS[24] high
+ * (RTS/DTR inactive) is the normal state with Iota VRPC controls
+ * NOT activated, whereas BDBUS[24] low (RTS or DTR active) turn ON
+ * the corresponding open drain control signal drivers.
+ *
+ * A special ftdi_sio driver quirk is needed in order to suppress
+ * automatic assertion of DTR & RTS on device open: this device's
+ * special PWON and RESET control drivers MUST NOT be activated
+ * when the port is ordinarily opened for plain serial communication,
+ * instead they must only be activated when a special userspace
+ * application explicitly requests such activation with a TIOCMBIS ioctl.
+ * These special userspace applications are responsible for making the
+ * needed pulse with a TIOCMBIS, delay, TIOCMBIC sequence.
+ *
+ * The special quirk must be applied only to FT2232D Channel B:
+ * Channel A is wired normally, with the chip's ADBUS2 and ADBUS4 outputs
+ * actually being RTS and DTR rather than something else.
+ */
+static void ftdi_duart28c_setup(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	struct usb_interface *intf = serial->interface;
+	int ifnum = intf->cur_altsetting->desc.bInterfaceNumber;
+
+	if (ifnum == 1)
+		priv->no_auto_dtr_rts = 1;
+}
+
 static void ftdi_port_remove(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
@@ -2385,10 +2427,18 @@ static void ftdi_dtr_rts(struct usb_serial_port *port, int on)
 			dev_err(&port->dev, "error from flowcontrol urb\n");
 		}
 	}
-	/* drop RTS and DTR */
-	if (on)
-		set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
-	else
+	/*
+	 * Assert or negate RTS and DTR as requested.  When DUART28C
+	 * quirk is applied, we suppress automatic assertion, but
+	 * automatic negation on device close is retained - these
+	 * special control signals are meant to be pulsed, and leaving
+	 * either of them stuck on when the responsible userspace
+	 * program has terminated unexpectedly is undesirable.
+	 */
+	if (on) {
+		if (!priv->no_auto_dtr_rts)
+			set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+	} else
 		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 }
 
@@ -2737,7 +2787,8 @@ static void ftdi_set_termios(struct tty_struct *tty,
 			dev_err(ddev, "%s urb failed to set baudrate\n", __func__);
 		mutex_unlock(&priv->cfg_lock);
 		/* Ensure RTS and DTR are raised when baudrate changed from 0 */
-		if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
+		if (old_termios && (old_termios->c_cflag & CBAUD) == B0
+		    && !priv->no_auto_dtr_rts)
 			set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 	}
 
diff --git a/drivers/usb/serial/ftdi_sio_ids.h b/drivers/usb/serial/ftdi_sio_ids.h
index e2099445db70..713c38190352 100644
--- a/drivers/usb/serial/ftdi_sio_ids.h
+++ b/drivers/usb/serial/ftdi_sio_ids.h
@@ -52,6 +52,7 @@
  */
 #define FTDI_FALCONIA_JTAG_BUF_PID	0x7150
 #define FTDI_FALCONIA_JTAG_UNBUF_PID	0x7151
+#define FTDI_FALCONIA_DUART28C_PID	0x7152
 
 /* Sienna Serial Interface by Secyourit GmbH */
 #define FTDI_SIENNA_PID		0x8348
-- 
2.9.0