Merge tag 'tty-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty / serial driver updates from Greg KH:
 "Here is the big set of tty and serial driver updates for 5.16-rc1.

  Nothing major in here at all, just lots of tiny serial and tty driver
  updates for various reported things, and some good cleanups. These
  include:

   - more good tty api cleanups from Jiri

   - stm32 serial driver updates

   - softlockup fix for non-preempt systems under high serial load

   - rpmsg serial driver update

   - 8250 drivers updates and fixes

   - n_gsm line discipline fixes and updates as people are finally
     starting to use it.

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

* tag 'tty-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (86 commits)
  tty: Fix extra "not" in TTY_DRIVER_REAL_RAW description
  serial: cpm_uart: Protect udbg definitions by CONFIG_SERIAL_CPM_CONSOLE
  tty: rpmsg: Define tty name via constant string literal
  tty: rpmsg: Add pr_fmt() to prefix messages
  tty: rpmsg: Use dev_err_probe() in ->probe()
  tty: rpmsg: Unify variable used to keep an error code
  tty: rpmsg: Assign returned id to a local variable
  serial: stm32: push DMA RX data before suspending
  serial: stm32: terminate / restart DMA transfer at suspend / resume
  serial: stm32: rework RX dma initialization and release
  serial: 8250_pci: Remove empty stub pci_quatech_exit()
  serial: 8250_pci: Replace custom pci_match_id() implementation
  serial: xilinx_uartps: Fix race condition causing stuck TX
  serial: sunzilog: Mark sunzilog_putchar() __maybe_unused
  Revert "tty: hvc: pass DMA capable memory to put_chars()"
  Revert "virtio-console: remove unnecessary kmemdup()"
  serial: 8250_pci: Replace dev_*() by pci_*() macros
  serial: 8250_pci: Get rid of redundant 'else' keyword
  serial: 8250_pci: Refactor the loop in pci_ite887x_init()
  tty: add rpmsg driver
  ...

2 files changed, 63 insertions, 10 deletions

diff --git a/Documentation/driver-api/serial/n_gsm.rst b/Documentation/driver-api/serial/n_gsm.rst
index 87dfcd54a96b..8fe723ab9c67 100644
--- a/Documentation/driver-api/serial/n_gsm.rst
+++ b/Documentation/driver-api/serial/n_gsm.rst
@@ -12,13 +12,16 @@ modems connected to a physical serial port.
 
 How to use it
 -------------
-1. initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
-   its serial port. Depending on the modem used, you can pass more or less
-   parameters to this command,
-2. switch the serial line to using the n_gsm line discipline by using
-   TIOCSETD ioctl,
-3. configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
-4. obtain base gsmtty number for the used serial port,
+1. config initiator
+^^^^^^^^^^^^^^^^^^^^^
+
+1.1 initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
+    its serial port. Depending on the modem used, you can pass more or less
+    parameters to this command.
+1.2 switch the serial line to using the n_gsm line discipline by using
+    TIOCSETD ioctl.
+1.3 configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl.
+1.4 obtain base gsmtty number for the used serial port.
 
 Major parts of the initialization program :
 (a good starting point is util-linux-ng/sys-utils/ldattach.c)::
@@ -70,14 +73,14 @@ Major parts of the initialization program :
 	daemon(0,0);
 	pause();
 
-5. use these devices as plain serial ports.
+1.5 use these devices as plain serial ports.
 
    for example, it's possible:
 
    - and to use gnokii to send / receive SMS on ttygsm1
    - to use ppp to establish a datalink on ttygsm2
 
-6. first close all virtual ports before closing the physical port.
+1.6 first close all virtual ports before closing the physical port.
 
    Note that after closing the physical port the modem is still in multiplexing
    mode. This may prevent a successful re-opening of the port later. To avoid
@@ -87,6 +90,56 @@ Major parts of the initialization program :
 
       0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9.
 
+2. config requester
+^^^^^^^^^^^^^^^^^^^^^
+
+2.1 receive string "AT+CMUX= command" through its serial port,initialize
+    mux mode config
+2.2 switch the serial line to using the n_gsm line discipline by using
+    TIOCSETD ioctl.
+2.3 configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl.
+2.4 obtain base gsmtty number for the used serial port,
+
+  #include <stdio.h>
+  #include <stdint.h>
+  #include <linux/gsmmux.h>
+  #include <linux/tty.h>
+  #define DEFAULT_SPEED	B115200
+  #define SERIAL_PORT	/dev/ttyS0
+
+	int ldisc = N_GSM0710;
+	struct gsm_config c;
+	struct termios configuration;
+	uint32_t first;
+
+	/* open the serial port */
+	fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
+
+	/* configure the serial port : speed, flow control ... */
+
+	/* get serial data and check "AT+CMUX=command" parameter ... */
+
+	/* use n_gsm line discipline */
+	ioctl(fd, TIOCSETD, &ldisc);
+
+	/* get n_gsm configuration */
+	ioctl(fd, GSMIOC_GETCONF, &c);
+	/* we are requester and need encoding 0 (basic) */
+	c.initiator = 0;
+	c.encapsulation = 0;
+	/* our modem defaults to a maximum size of 127 bytes */
+	c.mru = 127;
+	c.mtu = 127;
+	/* set the new configuration */
+	ioctl(fd, GSMIOC_SETCONF, &c);
+	/* get first gsmtty device node */
+	ioctl(fd, GSMIOC_GETFIRST, &first);
+	printf("first muxed line: /dev/gsmtty%i\n", first);
+
+	/* and wait for ever to keep the line discipline enabled */
+	daemon(0,0);
+	pause();
+
 Additional Documentation
 ------------------------
 More practical details on the protocol and how it's supported by industrial
diff --git a/Documentation/driver-api/serial/tty.rst b/Documentation/driver-api/serial/tty.rst
index dd972caacf3e..4b709f392713 100644
--- a/Documentation/driver-api/serial/tty.rst
+++ b/Documentation/driver-api/serial/tty.rst
@@ -58,7 +58,7 @@ close()			This is called on a terminal when the line
 hangup()		Called when the tty line is hung up.
 			The line discipline should cease I/O to the tty.
 			No further calls into the ldisc code will occur.
-			The return value is ignored. Can sleep.
+			Can sleep.
 
 read()			(optional) A process requests reading data from
 			the line. Multiple read calls may occur in parallel