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Lukas Wunner 7c622181fa serial: core: Initialize rs485 RTS polarity already on probe 
commit 2dd8a74fdd upstream.

RTS polarity of rs485-enabled ports is currently initialized on uart
open via:

tty_port_open()
  tty_port_block_til_ready()
    tty_port_raise_dtr_rts()  # if (C_BAUD(tty))
      uart_dtr_rts()
        uart_port_dtr_rts()

There's at least three problems here:

First, if no baud rate is set, RTS polarity is not initialized.
That's the right thing to do for rs232, but not for rs485, which
requires that RTS is deasserted unconditionally.

Second, if the DeviceTree property "linux,rs485-enabled-at-boot-time" is
present, RTS should be deasserted as early as possible, i.e. on probe.
Otherwise it may remain asserted until first open.

Third, even though RTS is deasserted on open and close, it may
subsequently be asserted by uart_throttle(), uart_unthrottle() or
uart_set_termios() because those functions aren't rs485-aware.
(Only uart_tiocmset() is.)

To address these issues, move RTS initialization from uart_port_dtr_rts()
to uart_configure_port().  Prevent subsequent modification of RTS
polarity by moving the existing rs485 check from uart_tiocmget() to
uart_update_mctrl().

That way, RTS is initialized on probe and then remains unmodified unless
the uart transmits data.  If rs485 is enabled at runtime (instead of at
boot) through a TIOCSRS485 ioctl(), RTS is initialized by the uart
driver's ->rs485_config() callback and then likewise remains unmodified.

The PL011 driver initializes RTS on uart open and prevents subsequent
modification in its ->set_mctrl() callback.  That code is obsoleted by
the present commit, so drop it.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Su Bao Cheng <baocheng.su@siemens.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/2d2acaf3a69e89b7bf687c912022b11fd29dfa1e.1642909284.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-06-25 15:18:40 +02:00
arch s390/mm: use non-quiescing sske for KVM switch to keyed guest 2022-06-25 15:18:40 +02:00
block block: Fix handling of offline queues in blk_mq_alloc_request_hctx() 2022-06-22 14:22:02 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: memneq - move into lib/ 2022-06-22 14:22:03 +02:00
Documentation x86/speculation/mmio: Add sysfs reporting for Processor MMIO Stale Data 2022-06-16 13:30:33 +02:00
drivers serial: core: Initialize rs485 RTS polarity already on probe 2022-06-25 15:18:40 +02:00
fs zonefs: fix zonefs_iomap_begin() for reads 2022-06-25 15:18:40 +02:00
include init: Initialize noop_backing_dev_info early 2022-06-22 14:22:02 +02:00
init Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 2022-06-09 10:23:26 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:23:10 +02:00
kernel bpf: Fix calling global functions from BPF_PROG_TYPE_EXT programs 2022-06-25 15:18:40 +02:00
lib crypto: memneq - move into lib/ 2022-06-22 14:22:03 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm init: Initialize noop_backing_dev_info early 2022-06-22 14:22:02 +02:00
net net: ax25: Fix deadlock caused by skb_recv_datagram in ax25_recvmsg 2022-06-22 14:22:01 +02:00
samples samples/landlock: Format with clang-format 2022-06-09 10:23:23 +02:00
scripts faddr2line: Fix overlapping text section failures, the sequel 2022-06-22 14:22:02 +02:00
security KEYS: trusted: tpm2: Fix migratable logic 2022-06-14 18:36:25 +02:00
sound ALSA: hda/realtek: fix right sounds and mute/micmute LEDs for HP machine 2022-06-22 14:22:05 +02:00
tools selftests/bpf: Add selftest for calling global functions from freplace 2022-06-25 15:18:40 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: avoid NULL pointer dereference in kvm_dirty_ring_push 2022-04-13 20:59:26 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add git tree for random.c 2022-05-30 09:28:59 +02:00
Makefile Linux 5.15.49 2022-06-22 14:22:05 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.