Merge tag 'tty-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty and serial driver updates from Greg KH:
 "Here is the big set of tty and serial driver updates for 5.19-rc1.

  Lots of tiny cleanups in here, the major stuff is:

   - termbit cleanups and unification by Ilpo. A much needed change that
     goes a long way to making things simpler for all of the different
     arches

   - tty documentation cleanups and movements to their own place in the
     documentation tree

   - old tty driver cleanups and fixes from Jiri to bring some existing
     drivers into the modern world

   - RS485 cleanups and unifications to make it easier for individual
     drivers to support this mode instead of having to duplicate logic
     in each driver

   - Lots of 8250 driver updates and additions

   - new device id additions

   - n_gsm continued fixes and cleanups

   - other minor serial driver updates and cleanups

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

* tag 'tty-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (166 commits)
  tty: Rework receive flow control char logic
  pcmcia: synclink_cs: Don't allow CS5-6
  serial: stm32-usart: Correct CSIZE, bits, and parity
  serial: st-asc: Sanitize CSIZE and correct PARENB for CS7
  serial: sifive: Sanitize CSIZE and c_iflag
  serial: sh-sci: Don't allow CS5-6
  serial: txx9: Don't allow CS5-6
  serial: rda-uart: Don't allow CS5-6
  serial: digicolor-usart: Don't allow CS5-6
  serial: uartlite: Fix BRKINT clearing
  serial: cpm_uart: Fix build error without CONFIG_SERIAL_CPM_CONSOLE
  serial: core: Do stop_rx in suspend path for console if console_suspend is disabled
  tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate.
  dt-bindings: serial: renesas,em-uart: Add RZ/V2M clock to access the registers
  serial: 8250_fintek: Check SER_RS485_RTS_* only with RS485
  Revert "serial: 8250_mtk: Make sure to select the right FEATURE_SEL"
  serial: msm_serial: disable interrupts in __msm_console_write()
  serial: meson: acquire port->lock in startup()
  serial: 8250_dw: Use dev_err_probe()
  serial: 8250_dw: Use devm_add_action_or_reset()
  ...

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index 8d60e0ff67b4..4f9264d005c0 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -87,6 +87,25 @@ config HVC_DCC
 	  driver. This console is used through a JTAG only on ARM. If you don't have
 	  a JTAG then you probably don't want this option.
 
+config HVC_DCC_SERIALIZE_SMP
+	bool "Use DCC only on CPU core 0"
+	depends on SMP && HVC_DCC
+	help
+	  This is a DEBUG option to serialize all console input and output to CPU 0.
+	  Some external debuggers, do not handle reads/writes from/to DCC on more
+	  than one CPU core. Each core has its own DCC device registers, so when a
+	  CPU core reads or writes from/to DCC, it only accesses its own DCC device.
+	  Since kernel code can run on any CPU core, every time the kernel wants to
+	  write to the console, it might write to a different DCC.
+
+	  In SMP mode, external debuggers create multiple windows, and each window
+	  shows the DCC output only from that core's DCC. The result is that
+	  console output is either lost or scattered across windows.
+
+	  Enable this option only if you are sure that you do not need features like
+	  CPU hotplug to work. For example, during early chipset bringups without
+	  debug serial console support. If unsure, say N.
+
 config HVC_RISCV_SBI
 	bool "RISC-V SBI console support"
 	depends on RISCV_SBI_V01