TTY/Serial driver fixes for 4.15-rc3

Here are some small serdev and serial fixes for 4.15-rc3.  They resolve
 some reported problems:
 	- a number of serdev fixes to resolve crashes
 	- MIPS build fixes for their serial port
 	- a new 8250 device id
 
 All of these have been in linux-next for a while with no reported
 issues.
 
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Merge tag 'tty-4.15-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial driver fixes from Greg KH:
 "Here are some small serdev and serial fixes for 4.15-rc3. They resolve
  some reported problems:

   - a number of serdev fixes to resolve crashes

   - MIPS build fixes for their serial port

   - a new 8250 device id

  All of these have been in linux-next for a while with no reported
  issues"

* tag 'tty-4.15-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  MIPS: Add custom serial.h with BASE_BAUD override for generic kernel
  serdev: ttyport: fix tty locking in close
  serdev: ttyport: fix NULL-deref on hangup
  serdev: fix receive_buf return value when no callback
  serdev: ttyport: add missing receive_buf sanity checks
  serial: 8250_early: Only set divisor if valid clk & baud
  serial: 8250_pci: Add Amazon PCI serial device ID

arch/mips/include/asm/Kbuild

@@ -16,7 +16,6 @@ generic-y += qrwlock.h
 generic-y += qspinlock.h
 generic-y += sections.h
 generic-y += segment.h
-generic-y += serial.h
 generic-y += trace_clock.h
 generic-y += unaligned.h
 generic-y += user.h

arch/mips/include/asm/serial.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2017 MIPS Tech, LLC
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ */
+#ifndef __ASM__SERIAL_H
+#define __ASM__SERIAL_H
+
+#ifdef CONFIG_MIPS_GENERIC
+/*
+ * Generic kernels cannot know a correct value for all platforms at
+ * compile time. Set it to 0 to prevent 8250_early using it
+ */
+#define BASE_BAUD 0
+#else
+#include <asm-generic/serial.h>
+#endif
+
+#endif /* __ASM__SERIAL_H */

drivers/tty/serdev/serdev-ttyport.c

@@ -27,23 +27,41 @@ static int ttyport_receive_buf(struct tty_port *port, const unsigned char *cp,
 {
 	struct serdev_controller *ctrl = port->client_data;
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	int ret;
 
 	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
 		return 0;
 
-	return serdev_controller_receive_buf(ctrl, cp, count);
+	ret = serdev_controller_receive_buf(ctrl, cp, count);
+
+	dev_WARN_ONCE(&ctrl->dev, ret < 0 || ret > count,
+				"receive_buf returns %d (count = %zu)\n",
+				ret, count);
+	if (ret < 0)
+		return 0;
+	else if (ret > count)
+		return count;
+
+	return ret;
 }
 
 static void ttyport_write_wakeup(struct tty_port *port)
 {
 	struct serdev_controller *ctrl = port->client_data;
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	struct tty_struct *tty;
 
-	if (test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &port->tty->flags) &&
+	tty = tty_port_tty_get(port);
+	if (!tty)
+		return;
+
+	if (test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags) &&
 	    test_bit(SERPORT_ACTIVE, &serport->flags))
 		serdev_controller_write_wakeup(ctrl);
 
-	wake_up_interruptible_poll(&port->tty->write_wait, POLLOUT);
+	wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
+
+	tty_kref_put(tty);
 }
 
 static const struct tty_port_client_operations client_ops = {
@@ -136,8 +154,10 @@ static void ttyport_close(struct serdev_controller *ctrl)
 
 	clear_bit(SERPORT_ACTIVE, &serport->flags);
 
+	tty_lock(tty);
 	if (tty->ops->close)
 		tty->ops->close(tty, NULL);
+	tty_unlock(tty);
 
 	tty_release_struct(tty, serport->tty_idx);
 }

drivers/tty/serial/8250/8250_early.c

@@ -122,12 +122,14 @@ static void __init init_port(struct earlycon_device *device)
 	serial8250_early_out(port, UART_FCR, 0);	/* no fifo */
 	serial8250_early_out(port, UART_MCR, 0x3);	/* DTR + RTS */
 
-	divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
-	c = serial8250_early_in(port, UART_LCR);
-	serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
-	serial8250_early_out(port, UART_DLL, divisor & 0xff);
-	serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
-	serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
+	if (port->uartclk && device->baud) {
+		divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
+		c = serial8250_early_in(port, UART_LCR);
+		serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
+		serial8250_early_out(port, UART_DLL, divisor & 0xff);
+		serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
+		serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
+	}
 }
 
 int __init early_serial8250_setup(struct earlycon_device *device,

drivers/tty/serial/8250/8250_pci.c

@@ -5135,6 +5135,9 @@ static const struct pci_device_id serial_pci_tbl[] = {
 	{ PCI_DEVICE(0x1601, 0x0800), .driver_data = pbn_b0_4_1250000 },
 	{ PCI_DEVICE(0x1601, 0xa801), .driver_data = pbn_b0_4_1250000 },
 
+	/* Amazon PCI serial device */
+	{ PCI_DEVICE(0x1d0f, 0x8250), .driver_data = pbn_b0_1_115200 },
+
 	/*
 	 * These entries match devices with class COMMUNICATION_SERIAL,
 	 * COMMUNICATION_MODEM or COMMUNICATION_MULTISERIAL

include/linux/serdev.h

@@ -184,7 +184,7 @@ static inline int serdev_controller_receive_buf(struct serdev_controller *ctrl,
 	struct serdev_device *serdev = ctrl->serdev;
 
 	if (!serdev || !serdev->ops->receive_buf)
-		return -EINVAL;
+		return 0;
 
 	return serdev->ops->receive_buf(serdev, data, count);
 }