uart_handle_break() and uart_prepare_sysrq_char() (in
include/linux/serial_core.h) capture a SysRq character into
port->sysrq_ch while the port lock is held and rely on the unlock
helper -- uart_unlock_and_check_sysrq_irqrestore() -- to dispatch the
captured character to handle_sysrq() on scope exit.
The existing guard(uart_port_lock_irqsave) cannot be used by IRQ
handlers that process RX, because its destructor calls plain
uart_port_unlock_irqrestore() and silently drops port->sysrq_ch.
Add a dedicated guard(uart_port_lock_check_sysrq_irqsave) variant
whose destructor is the sysrq-aware unlock helper. The lock side is
identical to uart_port_lock_irqsave -- only the unlock-time behaviour
differs. Callers that may capture SysRq characters must use
guard(uart_port_lock_check_sysrq_irqsave); the existing
guard(uart_port_lock_irqsave) keeps its current plain-unlock semantics
for the many callers that do not process RX.
The new macro is placed after the CONFIG_MAGIC_SYSRQ_SERIAL block so
both definitions of uart_unlock_and_check_sysrq_irqrestore() (sysrq
enabled and disabled) are visible at expansion time. When
CONFIG_MAGIC_SYSRQ_SERIAL=n the destructor degenerates to plain
uart_port_unlock_irqrestore(), so there is no overhead.
No functional change on its own; users are converted in the following
patches.
Cc: [email protected]
Signed-off-by: Jacques Nilo <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Link: https://patch.msgid.link/3849af4bc55d5d2a424fa850844e94d641b2f8a6.1778675349.git.jnilo@free.fr
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Having this, guards like these work:
guard(uart_port_lock_irq)(&up->port);
or
scoped_guard(uart_port_lock_irqsave, port) {
...
}
See e.g. "serial: 8250: use guard()s" later in this series.
Signed-off-by: "Jiri Slaby (SUSE)" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
The inline-defined constants look weird. Instead, define a proper enum
for them and type uart_port::iotype as that enum. This allows for proper
checking in switch-case labels (somewhere, a default or UPIO_UNKNOWN
label needs to be added/handled).
Signed-off-by: Jiri Slaby (SUSE) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
In a future patch HAS_IOPORT=n will disable inb()/outb() and friends at
compile time. We thus need to add HAS_IOPORT as dependency for those
drivers using them unconditionally. Some 8250 serial drivers support
MMIO only use, so fence only the parts requiring I/O ports and print an
error message if a device can't be supported with the current
configuration.
Co-developed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Maciej W. Rozycki <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Currently the port->lock wrappers uart_port_lock(),
uart_port_unlock() (and their variants) only lock/unlock
the spin_lock.
If the port is an nbcon console that has implemented the
write_atomic() callback, the wrappers must also acquire/release
the console context and mark the region as unsafe. This allows
general port->lock synchronization to be synchronized against
the nbcon write_atomic() callback.
Note that __uart_port_using_nbcon() relies on the port->lock
being held while a console is added and removed from the
console list (i.e. all uart nbcon drivers *must* take the
port->lock in their device_lock() callbacks).
Signed-off-by: John Ogness <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>
Introduce uart_port_set_cons() as a wrapper to set @cons of a
uart_port. The wrapper sets @cons under the port lock in order
to prevent @cons from disappearing while another context is
holding the port lock. This is necessary for a follow-up
commit relating to the port lock wrappers, which rely on @cons
not changing between lock and unlock.
Signed-off-by: John Ogness <[email protected]>
Tested-by: Théo Lebrun <[email protected]> # EyeQ5, AMBA-PL011
Acked-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>
It will be necessary at times for the uart nbcon console
drivers to acquire the port lock directly (without the
additional nbcon functionality of the port lock wrappers).
These are special cases such as the implementation of the
device_lock()/device_unlock() callbacks or for internal
port lock wrapper synchronization.
Provide low-level variants __uart_port_lock_irqsave() and
__uart_port_unlock_irqrestore() for this purpose.
Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>
This reverts commit 7bfb915a59.
This commit broke pxa and omap-serial, because it inhibited them from
calling stop_tx() if their TX FIFOs weren't completely empty. This
resulted in these two drivers hanging during transmits because the TX
interrupt would stay enabled, and a new TX interrupt would never fire.
Cc: [email protected]
Fixes: 7bfb915a59 ("serial: core: only stop transmit when HW fifo is empty")
Signed-off-by: Doug Brown <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
In some APIs we would like to assign the special value to iotype
and compare against it in another places. Introduce UPIO_UNKNOWN
for this purpose.
Note, we can't use 0, because it's a valid value for IO port access.
Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
If the circular buffer is empty, it just means we fit all characters to
send into the HW fifo, but not that the hardware finished transmitting
them.
So if we immediately call stop_tx() after that, this may abort any
pending characters in the HW fifo, and cause dropped characters on the
console.
Fix this by only stopping tx when the tx HW fifo is actually empty.
Fixes: 8275b48b27 ("tty: serial: introduce transmit helpers")
Cc: [email protected]
Signed-off-by: Jonas Gorski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
The function uart_fifo_timeout() returns an unsigned long value, which
is the number of jiffies. Therefore, change the variable timeout in the
function uart_poll_timeout() from int to unsigned long.
Change the return type of the function uart_poll_timeout() from int to
unsigned long to be consistent with the type of timeout values.
Signed-off-by: Vamshi Gajjela <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
When a serial port is used for kernel console output, then all
modifications to the UART registers which are done from other contexts,
e.g. getty, termios, are interference points for the kernel console.
So far this has been ignored and the printk output is based on the
principle of hope. The rework of the console infrastructure which aims to
support threaded and atomic consoles, requires to mark sections which
modify the UART registers as unsafe. This allows the atomic write function
to make informed decisions and eventually to restore operational state. It
also allows to prevent the regular UART code from modifying UART registers
while printk output is in progress.
All modifications of UART registers are guarded by the UART port lock,
which provides an obvious synchronization point with the console
infrastructure.
To avoid adding this functionality to all UART drivers, wrap the
spin_[un]lock*() invocations for uart_port::lock into helper functions
which just contain the spin_[un]lock*() invocations for now. In a
subsequent step these helpers will gain the console synchronization
mechanisms.
Converted with coccinelle. No functional change.
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
When a serial port is used for kernel console output, then all
modifications to the UART registers which are done from other contexts,
e.g. getty, termios, are interference points for the kernel console.
So far this has been ignored and the printk output is based on the
principle of hope. The rework of the console infrastructure which aims to
support threaded and atomic consoles, requires to mark sections which
modify the UART registers as unsafe. This allows the atomic write function
to make informed decisions and eventually to restore operational state. It
also allows to prevent the regular UART code from modifying UART registers
while printk output is in progress.
All modifications of UART registers are guarded by the UART port lock,
which provides an obvious synchronization point with the console
infrastructure.
Provide wrapper functions for spin_[un]lock*(port->lock) invocations so
that the console mechanics can be applied later on at a single place and
does not require to copy the same logic all over the drivers.
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
The serial core port id should be serial core controller specific port
instance, which is not always the port->line index.
For example, 8250 driver maps a number of legacy ports, and when a
hardware specific device driver takes over, we typically have one
driver instance for each port. Let's instead add port->port_id to
keep track serial ports mapped to each serial core controller instance.
Currently this is only a cosmetic issue for the serial core port device
names. The issue can be noticed looking at /sys/bus/serial-base/devices
for example though. Let's fix the issue to avoid port addressing issues
later on.
Fixes: 84a9582fd2 ("serial: core: Start managing serial controllers to enable runtime PM")
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
We want to enable runtime PM for serial port device drivers in a generic
way. To do this, we want to have the serial core layer manage the
registered physical serial controller devices.
To manage serial controllers, let's set up a struct bus and struct device
for the serial core controller as suggested by Greg and Jiri. The serial
core controller devices are children of the physical serial port device.
The serial core controller device is needed to support multiple different
kind of ports connected to single physical serial port device.
Let's also set up a struct device for the serial core port. The serial
core port instances are children of the serial core controller device.
With the serial core port device we can now flush pending TX on the
runtime PM resume as suggested by Johan.
Suggested-by: Andy Shevchenko <[email protected]>
Suggested-by: Greg Kroah-Hartman <[email protected]>
Suggested-by: Jiri Slaby <[email protected]>
Suggested-by: Johan Hovold <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
The return value is only ever used as a return value for remove callbacks
of platform drivers. This return value is ignored by the driver core.
(The only effect is an error message, but uart_remove_one_port() already
emitted one in this case.)
So the return value isn't used at all and uart_remove_one_port() can be
changed to return void without any loss. Also this better matches the
Linux device model as remove functions are not supposed to fail.
Signed-off-by: Uwe Kleine-König <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Convert hw_stopped in uart_port to bool because its more appropriate
type for how it is used.
Also convert the local variable in uart_change_line_settings() caching
old hw_stopped to bool.
Signed-off-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Convert uart_handle_cts_change() to bool which is more appropriate
than unsigned int.
Rename status to active to better describe what the parameter means.
While at it, make the comment about the active parameter easier to
parse.
Cleanup callsites from operations that are not necessary with bool.
Reviewed-by: Jiri Slaby <[email protected]>
Signed-off-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This patch provides a generic GPIO variable for outputting the state
of RS485 RX_DURING_TX. The GPIO is defined by the devicetree property
"rs485-rx-during-tx-gpios". To use it in a low level serial driver,
the evaluation of this variable must be implemented there accordingly.
Signed-off-by: Christoph Niedermaier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Now that the clock frequency is also part of the options, 16 bytes is
too little.
Without this patch dmesg does not show the whole options, Eg:
earlycon: uart0 at MMIO32 0x00000000fedc9000 (options '115200n8,480000')
instead of: '115200n8,48000000'
Signed-off-by: Ricardo Ribalda <[email protected]>
Reviewed-by: Jiri Slaby <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Pull tty/serial driver updates from Greg KH:
"Here is the "big" set of tty/serial driver changes for 6.2-rc1.
As in previous kernel releases, nothing big here at all, just some
small incremental serial/tty layer cleanups and some individual driver
additions and fixes. Highlights are:
- serial helper macros from Jiri Slaby to reduce the amount of
duplicated code in serial drivers
- api cleanups and consolidations from Ilpo Järvinen in lots of
serial drivers
- the usual set of n_gsm fixes from Daniel Starke as that code gets
exercised more
- TIOCSTI is finally able to be disabled if requested (security
hardening feature from Kees Cook)
- fsl_lpuart driver fixes and features added
- other small serial driver additions and fixes
All of these have been in linux-next for a while with no reported
problems"
* tag 'tty-6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (97 commits)
serial: atmel: don't stop the transmitter when doing PIO
serial: atmel: cleanup atmel_start+stop_tx()
tty: serial: fsl_lpuart: switch to new dmaengine_terminate_* API
serial: sunsab: Fix error handling in sunsab_init()
serial: altera_uart: fix locking in polling mode
serial: pch: Fix PCI device refcount leak in pch_request_dma()
tty: serial: fsl_lpuart: Use pm_ptr() to avoid need to make pm __maybe_unused
tty: serial: fsl_lpuart: Add runtime pm support
tty: serial: fsl_lpuart: enable wakeup source for lpuart
serdev: Replace poll loop by readx_poll_timeout() macro
tty: synclink_gt: unwind actions in error path of net device open
serial: stm32: move dma_request_chan() before clk_prepare_enable()
dt-bindings: serial: xlnx,opb-uartlite: Drop 'contains' from 'xlnx,use-parity'
serial: pl011: Do not clear RX FIFO & RX interrupt in unthrottle.
serial: amba-pl011: avoid SBSA UART accessing DMACR register
tty: serial: altera_jtaguart: remove struct altera_jtaguart
tty: serial: altera_jtaguart: use uart_port::read_status_mask
tty: serial: altera_jtaguart: remove unused altera_jtaguart::sigs
tty: serial: altera_jtaguart: remove flag from altera_jtaguart_rx_chars()
n_tty: Rename tail to old_tail in n_tty_read()
...
All users of uart_console_enabled() really want to know if a console
is registered. It is not reliable to check for CON_ENABLED in order
to identify if a console is registered. Use console_is_registered()
instead.
A _locked() variant is provided because uart_set_options() is always
called with the console_list_lock held and must check if a console
is registered in order to synchronize with kgdboc.
Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Many serial drivers do the same thing:
* send x_char if set
* keep sending from the xmit circular buffer until either
- the loop reaches the end of the xmit buffer
- TX is stopped
- HW fifo is full
* check for pending characters and:
- wake up tty writers to fill for more data into xmit buffer
- stop TX if there is nothing in the xmit buffer
The only differences are:
* how to write the character to the HW fifo
* the check of the end condition:
- is the HW fifo full?
- is limit of the written characters reached?
So unify the above into two helpers:
* uart_port_tx_limited() -- it performs the above taking the written
characters limit into account, and
* uart_port_tx() -- the same as above, except it only checks the HW
readiness, not the characters limit.
The HW specific operations (as stated as "differences" above) are passed
as arguments to the macros. They are:
* tx_ready -- returns true if HW can accept more data.
* put_char -- write a character to the device.
* tx_done -- when the write loop is done, perform arbitrary action
before potential invocation of ops->stop_tx() happens.
Note that the above are macros. This means the code is generated in
place and the above 3 arguments are "inlined". I.e. no added penalty by
generating call instructions for every single character. Nor any
indirect calls. (As in some previous versions of this patchset.)
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Jiri Slaby (SUSE) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
When a UART port is newly registered, uart_configure_port() seeks to
deassert RS485 Transmit Enable by setting the RTS bit in port->mctrl.
However a number of UART drivers interpret a set RTS bit as *assertion*
instead of deassertion: Affected drivers include those using
serial8250_em485_config() (except 8250_bcm2835aux.c) and some using
mctrl_gpio (e.g. imx.c).
Since the interpretation of the RTS bit is driver-specific, it is not
suitable as a means to centrally deassert Transmit Enable in the serial
core. Instead, the serial core must call on drivers to deassert it in
their driver-specific way. One way to achieve that is to call
->rs485_config(). It implicitly deasserts Transmit Enable.
So amend uart_configure_port() and uart_resume_port() to invoke
uart_rs485_config(). That allows removing calls to uart_rs485_config()
from drivers' ->probe() hooks and declaring the function static.
Skip any invocation of ->set_mctrl() if RS485 is enabled. RS485 has no
hardware flow control, so the modem control lines are irrelevant and
need not be touched. When leaving RS485 mode, reset the modem control
lines to the state stored in port->mctrl. That way, UARTs which are
muxed between RS485 and RS232 transceivers drive the lines correctly
when switched to RS232. (serial8250_do_startup() historically raises
the OUT1 modem signal because otherwise interrupts are not signaled on
ancient PC UARTs, but I believe that no longer applies to modern,
RS485-capable UARTs and is thus safe to be skipped.)
imx.c modifies port->mctrl whenever Transmit Enable is asserted and
deasserted. Stop it from doing that so port->mctrl reflects the RS232
line state.
8250_omap.c deasserts Transmit Enable on ->runtime_resume() by calling
->set_mctrl(). Because that is now a no-op in RS485 mode, amend the
function to call serial8250_em485_stop_tx().
fsl_lpuart.c retrieves and applies the RS485 device tree properties
after registering the UART port. Because applying now happens on
registration in uart_configure_port(), move retrieval of the properties
ahead of uart_add_one_port().
Link: https://lore.kernel.org/all/[email protected]/
Link: https://lore.kernel.org/all/[email protected]/
Fixes: d3b3404df3 ("serial: Fix incorrect rs485 polarity on uart open")
Cc: [email protected] # v4.14+
Reported-by: Matthias Schiffer <[email protected]>
Reported-by: Roosen Henri <[email protected]>
Tested-by: Matthias Schiffer <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Lukas Wunner <[email protected]>
Link: https://lore.kernel.org/r/2de36eba3fbe11278d5002e4e501afe0ceaca039.1663863805.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Use BIT_ULL rather than encoding bits explicitly where applicable with
UART port flags. This makes a (__force upf_t) cast redundant, but keep
it for visual consistency with the flags defined in terms of userspace
macros.
Signed-off-by: Maciej W. Rozycki <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
A SERIAL_8250_16550A_VARIANTS configuration option has been recently
defined that lets one request the 8250 driver not to probe for 16550A
device features so as to reduce the driver's device startup time in
virtual machines.
Some actual hardware devices require these features to have been fully
determined however for their driver to work correctly, so define a flag
to let drivers request full 16550A feature probing on a device-by-device
basis if required regardless of the SERIAL_8250_16550A_VARIANTS option
setting chosen.
Fixes: dc56ecb81a ("serial: 8250: Support disabling mdelay-filled probes of 16550A variants")
Cc: [email protected] # v5.6+
Reported-by: Anders Blomdell <[email protected]>
Signed-off-by: Maciej W. Rozycki <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Pull tty / serial driver updates from Greg KH:
"Here is the big set of tty and serial driver changes for 6.0-rc1.
It was delayed from last week as I wanted to make sure the last commit
here got some good testing in linux-next and elsewhere as it seemed to
show up only late in testing for some reason.
Nothing major here, just lots of cleanups from Jiri and Ilpo to make
the tty core cleaner (Jiri) and the rs485 code simpler to use (Ilpo).
Also included in here is the obligatory n_gsm updates from Daniel
Starke and lots of tiny driver updates and minor fixes and tweaks for
other smaller serial drivers.
All of these have been in linux-next for a while with no reported
problems"
* tag 'tty-6.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (186 commits)
tty: serial: qcom-geni-serial: Fix %lu -> %u in print statements
tty: amiserial: Fix comment typo
tty: serial: document uart_get_console()
tty: serial: serial_core, reformat kernel-doc for functions
Documentation: serial: link uart_ops properly
Documentation: serial: move GPIO kernel-doc to the functions
Documentation: serial: dedup kernel-doc for uart functions
Documentation: serial: move uart_ops documentation to the struct
dt-bindings: serial: snps-dw-apb-uart: Document Rockchip RV1126
serial: mvebu-uart: uart2 error bits clearing
tty: serial: fsl_lpuart: correct the count of break characters
serial: stm32: make info structs static to avoid sparse warnings
serial: fsl_lpuart: zero out parity bit in CS7 mode
tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate.
serial: 8250_bcm2835aux: Add missing clk_disable_unprepare()
tty: vt: initialize unicode screen buffer
serial: remove VR41XX serial driver
serial: 8250: lpc18xx: Remove redundant sanity check for RS485 flags
serial: 8250_dwlib: remove redundant sanity check for RS485 flags
dt_bindings: rs485: Correct delay values
...
While it's a lot of text, it always helps to keep it up to date when
it's by the source. (And not in a separate file.)
The documentation tooling also makes sure that all members of the
structure are documented. (If not, it complains loudly.)
Finally, there needs to be no comments inlined in the structure, so they
are dropped as they are superfluous now.
The compilation time of this header (tested with serial_core.c) didn't
change in my testing at all.
Signed-off-by: Jiri Slaby <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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 82586a7215 ("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: bedb404e91 ("serial: 8250_port: Don't use power management for kernel console")
Cc: stable <[email protected]>
Tested-by: Tony Lindgren <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Tony Lindgren <[email protected]>
Signed-off-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Jacques Nilo