linux-stable.git/drivers/tty/serial/serial_core.c, branch linux-5.18.y

serial: 8250: Fix PM usage_count for console handover

2022-07-22T08:21:58+00:00

commit f9b11229b79c0fb2100b5bb4628a101b1d37fbf6 upstream.

When console is enabled, univ8250_console_setup() calls
serial8250_console_setup() before .dev is set to uart_port. Therefore,
it will not call pm_runtime_get_sync(). Later, when the actual driver
is going to take over univ8250_console_exit() is called. As .dev is
already set, serial8250_console_exit() makes pm_runtime_put_sync() call
with usage count being zero triggering PM usage count warning
(extra debug for univ8250_console_setup(), univ8250_console_exit(), and
serial8250_register_ports()):

[    0.068987] univ8250_console_setup ttyS0 nodev
[    0.499670] printk: console [ttyS0] enabled
[    0.717955] printk: console [ttyS0] printing thread started
[    1.960163] serial8250_register_ports assigned dev for ttyS0
[    1.976830] printk: console [ttyS0] disabled
[    1.976888] printk: console [ttyS0] printing thread stopped
[    1.977073] univ8250_console_exit ttyS0 usage:0
[    1.977075] serial8250 serial8250: Runtime PM usage count underflow!
[    1.977429] dw-apb-uart.6: ttyS0 at MMIO 0x4010006000 (irq = 33, base_baud = 115200) is a 16550A
[    1.977812] univ8250_console_setup ttyS0 usage:2
[    1.978167] printk: console [ttyS0] printing thread started
[    1.978203] printk: console [ttyS0] enabled

To fix the issue, call pm_runtime_get_sync() in
serial8250_register_ports() as soon as .dev is set for an uart_port
if it has console enabled.

This problem became apparent only recently because 82586a721595 ("PM:
runtime: Avoid device usage count underflows") added the warning
printout. I confirmed this problem also occurs with v5.18 (w/o the
warning printout, obviously).

Fixes: bedb404e91bb ("serial: 8250_port: Don't use power management for kernel console")
Cc: stable 
Tested-by: Tony Lindgren 
Reviewed-by: Andy Shevchenko 
Reviewed-by: Tony Lindgren 
Signed-off-by: Ilpo Järvinen 
Link: https://lore.kernel.org/r/b4f428e9-491f-daf2-2232-819928dc276e@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

serial: 8250: fix XOFF/XON sending when DMA is used

2022-03-18T12:30:54+00:00

When 8250 UART is using DMA, x_char (XON/XOFF) is never sent
to the wire. After this change, x_char is injected correctly.

Create uart_xchar_out() helper for sending the x_char out and
accounting related to it. It seems that almost every driver
does these same steps with x_char. Except for 8250, however,
almost all currently lack .serial_out so they cannot immediately
take advantage of this new helper.

The downside of this patch is that it might reintroduce
the problems some devices faced with mixed DMA/non-DMA transfer
which caused revert f967fc8f165f (Revert "serial: 8250_dma:
don't bother DMA with small transfers"). However, the impact
should be limited to cases with XON/XOFF (that didn't work
with DMA capable devices to begin with so this problem is not
very likely to cause a major issue, if any at all).

Fixes: 9ee4b83e51f74 ("serial: 8250: Add support for dmaengine")
Reported-by: Gilles Buloz 
Tested-by: Gilles Buloz 
Reviewed-by: Andy Shevchenko 
Signed-off-by: Ilpo Järvinen 
Link: https://lore.kernel.org/r/20220314091432.4288-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

serial: make uart_console_write->putchar()'s character an unsigned char

2022-03-03T14:06:31+00:00

Currently, uart_console_write->putchar's second parameter (the
character) is of type int. It makes little sense, provided uart_console_write()
accepts the input string as "const char *s" and passes its content -- the
characters -- to putchar(). So switch the character's type to unsigned
char.

We don't use char as that is signed on some platforms. That would cause
troubles for drivers which (implicitly) cast the char to u16 when
writing to the device. Sign extension would happen in that case and the
value written would be completely different to the provided char. DZ is
an example of such a driver -- on MIPS, it uses u16 for dz_out in
dz_console_putchar().

Note we do the char -> uchar conversion implicitly in
uart_console_write(). Provided we do not change size of the data type,
sign extension does not happen there, so the problem is void.

This makes the types consistent and unified with the rest of the uart
layer, which uses unsigned char in most places already. One exception is
xmit_buf, but that is going to be converted later.

Cc: Paul Cercueil 
Cc: Tobias Klauser 
Cc: Russell King 
Cc: Vineet Gupta 
Cc: Nicolas Ferre 
Cc: Alexandre Belloni 
Cc: Ludovic Desroches 
Cc: Florian Fainelli 
Cc: bcm-kernel-feedback-list@broadcom.com
Cc: Alexander Shiyan 
Cc: Baruch Siach 
Cc: "Maciej W. Rozycki" 
Cc: Paul Walmsley 
Cc: Palmer Dabbelt 
Cc: Albert Ou 
Cc: Shawn Guo 
Cc: Sascha Hauer 
Cc: Pengutronix Kernel Team 
Cc: Fabio Estevam 
Cc: NXP Linux Team 
Cc: Karol Gugala 
Cc: Mateusz Holenko 
Cc: Vladimir Zapolskiy 
Cc: Neil Armstrong 
Cc: Kevin Hilman 
Cc: Jerome Brunet 
Cc: Martin Blumenstingl 
Cc: Taichi Sugaya 
Cc: Takao Orito 
Cc: Liviu Dudau 
Cc: Sudeep Holla 
Cc: Lorenzo Pieralisi 
Cc: "Andreas Färber" 
Cc: Manivannan Sadhasivam 
Cc: Michael Ellerman 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Andy Gross 
Cc: Bjorn Andersson 
Cc: Krzysztof Kozlowski 
Cc: Orson Zhai 
Cc: Baolin Wang 
Cc: Chunyan Zhang 
Cc: Patrice Chotard 
Cc: Maxime Coquelin 
Cc: Alexandre Torgue 
Cc: "David S. Miller" 
Cc: Peter Korsgaard 
Cc: Michal Simek 
Acked-by: Richard Genoud  [atmel_serial]
Acked-by: Uwe Kleine-König 
Acked-by: Paul Cercueil 
Acked-by: Neil Armstrong  # meson_serial
Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20220303080831.21783-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

serial: core: Drop duplicate NULL check in uart_*shutdown()

2022-02-04T15:58:59+00:00

The free_page(addr), which becomes free_pages(addr, 0) checks addr
against 0. No need to repeat this check in the callers.

Acked-by: Jiri Slaby 
Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20220204152808.10808-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

Merge tag 'v5.17-rc2' into tty-next

2022-01-30T14:24:36+00:00

We need the tty/serial fixes in here as well.

Signed-off-by: Greg Kroah-Hartman

serial: core: clean up EXPORT_SYMBOLs

2022-01-26T13:54:48+00:00

Some EXPORT_SYMBOLs are grouped at one location. Some follow functions
they export, but a newline is present before them. Fix all these and
move them where they belong.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20220124071430.14907-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

serial: core: Initialize rs485 RTS polarity already on probe

2022-01-26T13:53:12+00:00

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 
Cc: Su Bao Cheng 
Signed-off-by: Lukas Wunner 
Link: https://lore.kernel.org/r/2d2acaf3a69e89b7bf687c912022b11fd29dfa1e.1642909284.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman

serial: core: Keep mctrl register state and cached copy in sync

2022-01-06T15:01:48+00:00

struct uart_port contains a cached copy of the Modem Control signals.
It is used to skip register writes in uart_update_mctrl() if the new
signal state equals the old signal state.  It also avoids a register
read to obtain the current state of output signals.

When a uart_port is registered, uart_configure_port() changes signal
state but neglects to keep the cached copy in sync.  That may cause
a subsequent register write to be incorrectly skipped.  Fix it before
it trips somebody up.

This behavior has been present ever since the serial core was introduced
in 2002:
https://git.kernel.org/history/history/c/33c0d1b0c3eb

So far it was never an issue because the cached copy is initialized to 0
by kzalloc() and when uart_configure_port() is executed, at most DTR has
been set by uart_set_options() or sunsu_console_setup().  Therefore,
a stable designation seems unnecessary.

Signed-off-by: Lukas Wunner 
Link: https://lore.kernel.org/r/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman

serial: Fix incorrect rs485 polarity on uart open

2021-12-30T12:21:02+00:00

Commit a6845e1e1b78 ("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: a6845e1e1b78 ("serial: core: Consider rs485 settings to drive RTS")
Cc: stable@vger.kernel.org # v4.14+
Cc: Rafael Gago Castano 
Cc: Jan Kiszka 
Cc: Su Bao Cheng 
Signed-off-by: Lukas Wunner 
Link: https://lore.kernel.org/r/9395767847833f2f3193c49cde38501eeb3b5669.1639821059.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman

Merge 5.16-rc4 into tty-next

2021-12-06T08:32:47+00:00

We need the tty/serial driver fixes in here as well.

Signed-off-by: Greg Kroah-Hartman