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Filename Latest commit message Latest commit date
Lukas Wunner c526d53edd serial: Fix incorrect rs485 polarity on uart open
commit d3b3404df318504ec084213ab1065b73f49b0f1d upstream.

Commit a6845e1e1b ("serial: core: Consider rs485 settings to drive
RTS") sought to deassert RTS when opening an rs485-enabled uart port.
That way, the transceiver does not occupy the bus until it transmits
data.

Unfortunately, the commit mixed up the logic and *asserted* RTS instead
of *deasserting* it:

The commit amended uart_port_dtr_rts(), which raises DTR and RTS when
opening an rs232 port.  "Raising" actually means lowering the signal
that's coming out of the uart, because an rs232 transceiver not only
changes a signal's voltage level, it also *inverts* the signal.  See
the simplified schematic in the MAX232 datasheet for an example:
https://www.ti.com/lit/ds/symlink/max232.pdf

So, to raise RTS on an rs232 port, TIOCM_RTS is *set* in port->mctrl
and that results in the signal being driven low.

In contrast to rs232, the signal level for rs485 Transmit Enable is the
identity, not the inversion:  If the transceiver expects a "high" RTS
signal for Transmit Enable, the signal coming out of the uart must also
be high, so TIOCM_RTS must be *cleared* in port->mctrl.

The commit did the exact opposite, but it's easy to see why given the
confusing semantics of rs232 and rs485.  Fix it.

Fixes: a6845e1e1b ("serial: core: Consider rs485 settings to drive RTS")
Cc: stable@vger.kernel.org # v4.14+
Cc: Rafael Gago Castano <rgc@hms.se>
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/9395767847833f2f3193c49cde38501eeb3b5669.1639821059.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-01-27 09:19:49 +01:00
arch MIPS: Octeon: Fix build errors using clang 2022-01-27 09:19:48 +01:00
block block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2) 2021-12-14 14:49:02 +01:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-15 09:47:29 +02:00
crypto crypto: pcrypt - Delay write to padata->info 2021-11-17 09:48:40 +01:00
Documentation Input: i8042 - add deferred probe support 2022-01-05 12:37:43 +01:00
drivers serial: Fix incorrect rs485 polarity on uart open 2022-01-27 09:19:49 +01:00
fs fuse: Pass correct lend value to filemap_write_and_wait_range() 2022-01-27 09:19:49 +01:00
include ACPICA: actypes.h: Expand the ACPI_ACCESS_ definitions 2022-01-27 09:19:45 +01:00
init
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-12-01 09:23:35 +01:00
kernel audit: ensure userspace is penalized the same as the kernel when under pressure 2022-01-27 09:19:44 +01:00
lib siphash: use _unaligned version by default 2021-12-08 09:01:12 +01:00
LICENSES
mm shmem: fix a race between shmem_unused_huge_shrink and shmem_evict_inode 2022-01-27 09:19:29 +01:00
net mac80211: allow non-standard VHT MCS-10/11 2022-01-27 09:19:46 +01:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-17 09:48:39 +01:00
scripts recordmcount.pl: fix typo in s390 mcount regex 2022-01-05 12:37:44 +01:00
security selinux: fix potential memleak in selinux_add_opt() 2022-01-27 09:19:35 +01:00
sound ASoC: mediatek: mt8173: fix device_node leak 2022-01-27 09:19:48 +01:00
tools bpftool: Enable line buffering for stdout 2022-01-27 09:19:35 +01:00
usr
virt KVM: do not shrink halt_poll_ns below grow_start 2021-10-09 14:39:50 +02:00
.clang-format
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Makefile Linux 5.4.173 2022-01-20 09:19:19 +01:00
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