Merge tag 'tty-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty / serial updates from Greg KH:
 "Here is the big set of tty/serial driver updates for 6.4-rc1.

  Nothing major, just lots of tiny, constant, forward development. This
  includes:

   - obligatory n_gsm updates and feature additions

   - 8250_em driver updates

   - sh-sci driver updates

   - dts cleanups and updates

   - general cleanups and improvements by Ilpo and Jiri

   - other small serial driver core fixes and driver updates

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

* tag 'tty-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (87 commits)
  n_gsm: Use array_index_nospec() with index that comes from userspace
  tty: vt: drop checks for undefined VT_SINGLE_DRIVER
  tty: vt: distribute EXPORT_SYMBOL()
  tty: vt: simplify some cases in tioclinux()
  tty: vt: reformat tioclinux()
  tty: serial: sh-sci: Fix end of transmission on SCI
  tty: serial: sh-sci: Add support for tx end interrupt handling
  tty: serial: sh-sci: Fix TE setting on SCI IP
  tty: serial: sh-sci: Add RZ/G2L SCIFA DMA rx support
  tty: serial: sh-sci: Add RZ/G2L SCIFA DMA tx support
  serial: max310x: fix IO data corruption in batched operations
  serial: core: Disable uart_start() on uart_remove_one_port()
  serial: 8250: Reinit port->pm on port specific driver unbind
  serial: 8250: Add missing wakeup event reporting
  tty: serial: fsl_lpuart: use UARTMODIR register bits for lpuart32 platform
  tty: serial: fsl_lpuart: adjust buffer length to the intended size
  serial: fix TIOCSRS485 locking
  serial: make SiFive serial drivers depend on ARCH_ symbols
  tty: synclink_gt: don't allocate and pass dummy flags
  tty: serial: simplify qcom_geni_serial_send_chunk_fifo()
  ...

1 files changed, 33 insertions, 3 deletions

diff --git a/Documentation/admin-guide/serial-console.rst b/Documentation/admin-guide/serial-console.rst
index 58b32832e50a..8c8b94e54e26 100644
--- a/Documentation/admin-guide/serial-console.rst
+++ b/Documentation/admin-guide/serial-console.rst
@@ -33,8 +33,11 @@ The format of this option is::
 			9600n8. The maximum baudrate is 115200.
 
 You can specify multiple console= options on the kernel command line.
-Output will appear on all of them. The last device will be used when
-you open ``/dev/console``. So, for example::
+
+The behavior is well defined when each device type is mentioned only once.
+In this case, the output will appear on all requested consoles. And
+the last device will be used when you open ``/dev/console``.
+So, for example::
 
 	console=ttyS1,9600 console=tty0
 
@@ -42,7 +45,34 @@ defines that opening ``/dev/console`` will get you the current foreground
 virtual console, and kernel messages will appear on both the VGA
 console and the 2nd serial port (ttyS1 or COM2) at 9600 baud.
 
-Note that you can only define one console per device type (serial, video).
+The behavior is more complicated when the same device type is defined more
+times. In this case, there are the following two rules:
+
+1. The output will appear only on the first device of each defined type.
+
+2. ``/dev/console`` will be associated with the first registered device.
+   Where the registration order depends on how kernel initializes various
+   subsystems.
+
+   This rule is used also when the last console= parameter is not used
+   for other reasons. For example, because of a typo or because
+   the hardware is not available.
+
+The result might be surprising. For example, the following two command
+lines have the same result:
+
+	console=ttyS1,9600 console=tty0 console=tty1
+	console=tty0 console=ttyS1,9600 console=tty1
+
+The kernel messages are printed only on ``tty0`` and ``ttyS1``. And
+``/dev/console`` gets associated with ``tty0``. It is because kernel
+tries to register graphical consoles before serial ones. It does it
+because of the default behavior when no console device is specified,
+see below.
+
+Note that the last ``console=tty1`` parameter still makes a difference.
+The kernel command line is used also by systemd. It would use the last
+defined ``tty1`` as the login console.
 
 If no console device is specified, the first device found capable of
 acting as a system console will be used. At this time, the system