linux-stable.git/drivers/tty/serial, branch v6.18.41 Linux kernel stable tree serial: 8250_omap: clear rx_running on zero-length DMA completes 2026-07-24T14:15:41+00:00 Matthias Feser mfe@KBSgmbhfr.onmicrosoft.com 2026-05-26T07:35:09+00:00 2ecd118fb6913584a4889a4a778aef5283bae579 commit 061b627ba534230a18ec4d7251562af12325d06a upstream. On AM33xx RX DMA only triggers when the FIFO reaches the configured threshold (typically 48 bytes). For smaller bursts no DMA request is issued and the FIFO is drained by RX timeout. In this case __dma_rx_do_complete() can legitimately see count == 0. The current code exits early in this case and does not clear dma->rx_running, leaving the DMA state inconsistent. This can prevent RX DMA from restarting and may cause omap_8250_rx_dma_flush() to fail, marking DMA as broken. Fix this by clearing dma->rx_running once the DMA transfer has completed or been terminated, even if no data was transferred. Fixes: a5fd8945a478 ("serial: 8250: 8250_omap.c: Clear DMA RX running status only after DMA termination is done") Cc: stable <stable@kernel.org> Signed-off-by: Matthias Feser <mfe@KBSgmbhfr.onmicrosoft.com> Reviewed-by: Moteen Shah <m-shah@ti.com> Link: https://patch.msgid.link/BE3P281MB55155F2F5795E411F5A65282EE0B2@BE3P281MB5515.DEUP281.PROD.OUTLOOK.COM Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 061b627ba534230a18ec4d7251562af12325d06a upstream.

On AM33xx RX DMA only triggers when the FIFO reaches the
configured threshold (typically 48 bytes). For smaller bursts
no DMA request is issued and the FIFO is drained by RX timeout.

In this case __dma_rx_do_complete() can legitimately see count == 0.

The current code exits early in this case and does not clear
dma->rx_running, leaving the DMA state inconsistent. This can
prevent RX DMA from restarting and may cause
omap_8250_rx_dma_flush() to fail, marking DMA as broken.

Fix this by clearing dma->rx_running once the DMA transfer has
completed or been terminated, even if no data was transferred.

Fixes: a5fd8945a478 ("serial: 8250: 8250_omap.c: Clear DMA RX running status only after DMA termination is done")
Cc: stable <stable@kernel.org>
Signed-off-by: Matthias Feser <mfe@KBSgmbhfr.onmicrosoft.com>
Reviewed-by: Moteen Shah <m-shah@ti.com>
Link: https://patch.msgid.link/BE3P281MB55155F2F5795E411F5A65282EE0B2@BE3P281MB5515.DEUP281.PROD.OUTLOOK.COM
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: max310x: implement gpio_chip::get_direction() 2026-07-24T14:15:41+00:00 Tapio Reijonen tapio.reijonen@vaisala.com 2026-06-15T06:38:40+00:00 c37095c431c39000ce818d3ff568a61b0e0ee02a commit a483b1a91b33b7533280e7c3efd2bc1275caef18 upstream. It's strongly recommended for GPIO drivers to always implement the .get_direction() callback - even when the direction is tracked in software. The GPIO core emits a warning when the callback is missing and a user reads the direction of a line, e.g. via /sys/kernel/debug/gpio. The MAX310X keeps the GPIO direction in the GPIOCFG register (a set bit selects output), which the existing direction_input/output callbacks already program, so the current direction can be read back directly. Fixes: f65444187a66 ("serial: New serial driver MAX310X") Cc: stable <stable@kernel.org> Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com> Reviewed-by: Linus Walleij <linusw@kernel.org> Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com> Reviewed-by: Hugo Villeneuve <hvilleneuve@dimonoff.com> Link: https://patch.msgid.link/20260615-b4-serial-max310x-gpio-get-direction-v2-1-4704ba2b181a@vaisala.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit a483b1a91b33b7533280e7c3efd2bc1275caef18 upstream.

It's strongly recommended for GPIO drivers to always implement the
.get_direction() callback - even when the direction is tracked in
software. The GPIO core emits a warning when the callback is missing
and a user reads the direction of a line, e.g. via
/sys/kernel/debug/gpio.

The MAX310X keeps the GPIO direction in the GPIOCFG register (a set bit
selects output), which the existing direction_input/output callbacks
already program, so the current direction can be read back directly.

Fixes: f65444187a66 ("serial: New serial driver MAX310X")
Cc: stable <stable@kernel.org>
Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://patch.msgid.link/20260615-b4-serial-max310x-gpio-get-direction-v2-1-4704ba2b181a@vaisala.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: msm: Disable DMA for kernel console UART 2026-07-24T14:15:41+00:00 Stephan Gerhold stephan.gerhold@linaro.org 2026-07-06T18:03:32+00:00 d354716245192de2d203f2b35f22ab8dc13595e2 commit 22dd2777e6c180e1c945b00f6d18550979436324 upstream. At the moment, concurrent writes from userspace and the kernel to the console can trigger a race condition that results in an infinite loop of the same messages printed over and over again. This is most likely to happen during system startup or shutdown when the init system starts/stops a large number of system services that interact with various kernel code. When userspace writes to the TTY device, the driver initiates an asynchronous DMA transfer and releases the port lock. At the same moment, the kernel printk path might grab the port lock and re-configure the UART controller for PIO, without waiting for the DMA operation to complete. It seems like this collision results in zero progress being reported for the DMA engine, so the same text is printed to the console over and over again. For the kernel console, we want a reliable output path that will be functional even during crashes etc. So rather than implementing complex code to synchronize the kernel console write routines with the userspace DMA write routines, simply disable DMA for the console UART instance. Similar checks exist in many other serial drivers, e.g. 8250_port.c, imx.c, sh-sci.c etc. Cc: stable <stable@kernel.org> Fixes: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support") Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org> Acked-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com> Link: https://patch.msgid.link/20260706-serial-msm-console-dma-collision-v1-1-3179b8cb1d89@linaro.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 22dd2777e6c180e1c945b00f6d18550979436324 upstream.

At the moment, concurrent writes from userspace and the kernel to the
console can trigger a race condition that results in an infinite loop of
the same messages printed over and over again. This is most likely to
happen during system startup or shutdown when the init system starts/stops
a large number of system services that interact with various kernel code.

When userspace writes to the TTY device, the driver initiates an
asynchronous DMA transfer and releases the port lock. At the same moment,
the kernel printk path might grab the port lock and re-configure the UART
controller for PIO, without waiting for the DMA operation to complete. It
seems like this collision results in zero progress being reported for the
DMA engine, so the same text is printed to the console over and over again.

For the kernel console, we want a reliable output path that will be
functional even during crashes etc. So rather than implementing complex
code to synchronize the kernel console write routines with the userspace
DMA write routines, simply disable DMA for the console UART instance.

Similar checks exist in many other serial drivers, e.g. 8250_port.c,
imx.c, sh-sci.c etc.

Cc: stable <stable@kernel.org>
Fixes: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support")
Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Acked-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://patch.msgid.link/20260706-serial-msm-console-dma-collision-v1-1-3179b8cb1d89@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: 8250_mid: Disable DMA for selected platforms 2026-07-18T14:53:22+00:00 Andy Shevchenko andriy.shevchenko@linux.intel.com 2026-06-26T09:49:37+00:00 1cd54e217c6e2cdb794a897b2f855e13ffcee586 commit b1b4efea05a56c0995e4702a86d6624b4fdff32f upstream. In accordance with Errata (specification updates) HSUART May Stop Functioning when DMA is Active. - Denverton document #572409, rev 3.4, DNV60 - Ice Lake Xeon D document #714070, ICXD65 - Snowridge document #731931, SNR44 For a quick fix just disable the respective callbacks during the device probe. Depending on the future development we might remove them completely. Reported-by: micas-opensource <zjianan156@gmail.com> Closes: https://lore.kernel.org/linux-serial/20250625031409.2404219-1-opensource@ruijie.com.cn/ Fixes: 6ede6dcd87aa ("serial: 8250_mid: add support for DMA engine handling from UART MMIO") Cc: stable <stable@kernel.org> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://patch.msgid.link/20260626094937.561776-1-andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit b1b4efea05a56c0995e4702a86d6624b4fdff32f upstream.

In accordance with Errata (specification updates)
HSUART May Stop Functioning when DMA is Active.

- Denverton document #572409, rev 3.4, DNV60
- Ice Lake Xeon D document #714070, ICXD65
- Snowridge document #731931, SNR44

For a quick fix just disable the respective callbacks during the device probe.
Depending on the future development we might remove them completely.

Reported-by: micas-opensource <zjianan156@gmail.com>
Closes: https://lore.kernel.org/linux-serial/20250625031409.2404219-1-opensource@ruijie.com.cn/
Fixes: 6ede6dcd87aa ("serial: 8250_mid: add support for DMA engine handling from UART MMIO")
Cc: stable <stable@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260626094937.561776-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: 8250_dw: unregister 8250 port if clk_notifier_register() fails 2026-07-04T11:44:21+00:00 Stepan Ionichev sozdayvek@gmail.com 2026-05-14T14:37:45+00:00 3d205fe80f2181f0109150ad1fa06ee5bc046935 commit 10fc708b4de7f86002d2d735a2dbf3b5b7f65692 upstream. dw8250_probe() registers the 8250 port via serial8250_register_8250_port() and then, if the device has a clock, registers a clock notifier. If clk_notifier_register() fails, probe returns the error but leaves the 8250 port registered. The matching serial8250_unregister_port() lives in dw8250_remove(), which is not called when probe fails, so the port slot stays occupied until the device is rebound or the system is rebooted. The devm-allocated driver data is freed while the port still references it (via the saved private_data and serial_in/serial_out callbacks), so any access to that port slot before a rebind is a use-after-free hazard. Unregister the port on the clk_notifier_register() error path. Fixes: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition") Cc: stable@vger.kernel.org Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://patch.msgid.link/20260514143746.23671-2-sozdayvek@gmail.com Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 10fc708b4de7f86002d2d735a2dbf3b5b7f65692 upstream.

dw8250_probe() registers the 8250 port via serial8250_register_8250_port()
and then, if the device has a clock, registers a clock notifier. If
clk_notifier_register() fails, probe returns the error but leaves the
8250 port registered. The matching serial8250_unregister_port() lives
in dw8250_remove(), which is not called when probe fails, so the port
slot stays occupied until the device is rebound or the system is
rebooted. The devm-allocated driver data is freed while the port still
references it (via the saved private_data and serial_in/serial_out
callbacks), so any access to that port slot before a rebind is a
use-after-free hazard.

Unregister the port on the clk_notifier_register() error path.

Fixes: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition")
Cc: stable@vger.kernel.org
Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260514143746.23671-2-sozdayvek@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: qcom_geni: Fix RX DMA stall when SE_DMA_RX_LEN_IN is zero 2026-06-27T10:06:50+00:00 Viken Dadhaniya viken.dadhaniya@oss.qualcomm.com 2026-05-28T17:18:07+00:00 50b72074c5e8d6fe7d8c39c71277dba6d3ac225c commit b93062b6d8a1b2d9bad235cac25558a909819026 upstream. In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero, for example when the RX stale counter fires on an idle line, the handler returns without calling geni_se_rx_dma_prep(). The next RX DMA interrupt then hits the !port->rx_dma_addr guard and returns immediately, so the RX DMA buffer is never rearmed and later input is lost. Keep the handler on the rearm path when rx_in is zero. Warn about the unexpected zero-length DMA completion, skip received-data handling, and always call geni_se_rx_dma_prep(). Fixes: 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA") Cc: stable@vger.kernel.org Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com> Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com> Link: https://patch.msgid.link/20260528-serial-rx-0-byte-fix-v2-1-b4195cfe342f@oss.qualcomm.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit b93062b6d8a1b2d9bad235cac25558a909819026 upstream.

In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears
port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero,
for example when the RX stale counter fires on an idle line, the handler
returns without calling geni_se_rx_dma_prep().

The next RX DMA interrupt then hits the !port->rx_dma_addr guard and
returns immediately, so the RX DMA buffer is never rearmed and later input
is lost.

Keep the handler on the rearm path when rx_in is zero. Warn about the
unexpected zero-length DMA completion, skip received-data handling, and
always call geni_se_rx_dma_prep().

Fixes: 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")
Cc: stable@vger.kernel.org
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>
Link: https://patch.msgid.link/20260528-serial-rx-0-byte-fix-v2-1-b4195cfe342f@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: 8250_dw: dispatch SysRq character in dw8250_handle_irq() 2026-06-09T10:28:49+00:00 Jacques Nilo jnilo@free.fr 2026-05-13T13:30:25+00:00 71b88acec0a7142964b1a2b77faa5c51072244a2 commit 2e211723953f7740e54b53f3d3a0d5e351a5e223 upstream. dw8250_handle_irq() calls serial8250_handle_irq_locked() with the port lock held via guard(uart_port_lock_irqsave). The guard destructor is plain uart_port_unlock_irqrestore(), so a SysRq character captured into port->sysrq_ch by uart_prepare_sysrq_char() is dropped without ever being dispatched to handle_sysrq(). This is the same regression pattern as in serial8250_handle_irq(), introduced when 883c5a2bc934 ("serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling") moved the function to the guard()-based locking scheme without using the sysrq-aware unlock helper. Switch to guard(uart_port_lock_check_sysrq_irqsave) so that captured sysrq_ch is dispatched on scope exit, matching the fix in serial8250_handle_irq(). Fixes: 883c5a2bc934 ("serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling") Cc: stable@vger.kernel.org Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Signed-off-by: Jacques Nilo <jnilo@free.fr> Link: https://patch.msgid.link/ed56fcaf4af24e4ed011a7bce206e0182acb761c.1778675349.git.jnilo@free.fr Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 2e211723953f7740e54b53f3d3a0d5e351a5e223 upstream.

dw8250_handle_irq() calls serial8250_handle_irq_locked() with the port
lock held via guard(uart_port_lock_irqsave). The guard destructor is
plain uart_port_unlock_irqrestore(), so a SysRq character captured into
port->sysrq_ch by uart_prepare_sysrq_char() is dropped without ever
being dispatched to handle_sysrq().

This is the same regression pattern as in serial8250_handle_irq(),
introduced when 883c5a2bc934 ("serial: 8250_dw: Rework
dw8250_handle_irq() locking and IIR handling") moved the function to
the guard()-based locking scheme without using the sysrq-aware unlock
helper.

Switch to guard(uart_port_lock_check_sysrq_irqsave) so that captured
sysrq_ch is dispatched on scope exit, matching the fix in
serial8250_handle_irq().

Fixes: 883c5a2bc934 ("serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling")
Cc: stable@vger.kernel.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jacques Nilo <jnilo@free.fr>
Link: https://patch.msgid.link/ed56fcaf4af24e4ed011a7bce206e0182acb761c.1778675349.git.jnilo@free.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: 8250: dispatch SysRq character in serial8250_handle_irq() 2026-06-09T10:28:49+00:00 Jacques Nilo jnilo@free.fr 2026-05-13T13:30:24+00:00 7f8b194ed7206bc866d554b9f63f47e11d97c2c0 commit 71f42b2149a1307a97165b409493665579462ea0 upstream. serial8250_handle_irq() captures a SysRq character into port->sysrq_ch inside serial8250_handle_irq_locked() via uart_prepare_sysrq_char() (reached from serial8250_read_char()). Dispatch of that captured character to handle_sysrq() is expected to happen at port-unlock time, through uart_unlock_and_check_sysrq[_irqrestore](). After commit 8324a54f604d ("serial: 8250: Add serial8250_handle_irq_locked()") the function was reduced to a wrapper that takes the port lock via guard(uart_port_lock_irqsave) whose destructor is plain uart_port_unlock_irqrestore(). The sysrq-aware unlock helper is no longer called, so port->sysrq_ch is captured but never dispatched: BREAK + SysRq key is consumed silently. This was the very condition Johan Hovold's 853a9ae29e978 ("serial: 8250: fix handle_irq locking", 2021) introduced uart_unlock_and_check_sysrq_irqrestore() to address. Switch to the new guard(uart_port_lock_check_sysrq_irqsave), whose destructor is the sysrq-aware unlock helper, restoring the pre-split behaviour. Update the Context: comment on serial8250_handle_irq_locked() so future HW-specific 8250 wrappers know to use the same guard or the explicit sysrq-aware unlock. Verified on RTL8196E with CONFIG_MAGIC_SYSRQ_SERIAL=y: BREAK + 'h' on the console UART produces the SysRq help dump in dmesg and the brk counter in /proc/tty/driver/serial increments correctly. Fixes: 8324a54f604d ("serial: 8250: Add serial8250_handle_irq_locked()") Cc: stable@vger.kernel.org Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Signed-off-by: Jacques Nilo <jnilo@free.fr> Link: https://patch.msgid.link/52692ae6c3501f7940347cef364ad7fcacaab7e5.1778675349.git.jnilo@free.fr Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 71f42b2149a1307a97165b409493665579462ea0 upstream.

serial8250_handle_irq() captures a SysRq character into port->sysrq_ch
inside serial8250_handle_irq_locked() via uart_prepare_sysrq_char()
(reached from serial8250_read_char()). Dispatch of that captured
character to handle_sysrq() is expected to happen at port-unlock time,
through uart_unlock_and_check_sysrq[_irqrestore]().

After commit 8324a54f604d ("serial: 8250: Add
serial8250_handle_irq_locked()") the function was reduced to a wrapper
that takes the port lock via guard(uart_port_lock_irqsave) whose
destructor is plain uart_port_unlock_irqrestore(). The sysrq-aware
unlock helper is no longer called, so port->sysrq_ch is captured but
never dispatched: BREAK + SysRq key is consumed silently.

This was the very condition Johan Hovold's 853a9ae29e978 ("serial:
8250: fix handle_irq locking", 2021) introduced
uart_unlock_and_check_sysrq_irqrestore() to address.

Switch to the new guard(uart_port_lock_check_sysrq_irqsave), whose
destructor is the sysrq-aware unlock helper, restoring the pre-split
behaviour. Update the Context: comment on serial8250_handle_irq_locked()
so future HW-specific 8250 wrappers know to use the same guard or the
explicit sysrq-aware unlock.

Verified on RTL8196E with CONFIG_MAGIC_SYSRQ_SERIAL=y: BREAK + 'h' on
the console UART produces the SysRq help dump in dmesg and the brk
counter in /proc/tty/driver/serial increments correctly.

Fixes: 8324a54f604d ("serial: 8250: Add serial8250_handle_irq_locked()")
Cc: stable@vger.kernel.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jacques Nilo <jnilo@free.fr>
Link: https://patch.msgid.link/52692ae6c3501f7940347cef364ad7fcacaab7e5.1778675349.git.jnilo@free.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: zs: Convert to use a platform device 2026-06-09T10:28:49+00:00 Maciej W. Rozycki macro@orcam.me.uk 2026-05-06T22:42:52+00:00 237dc8c08de3cb293b6607aaee8b13b3a671e267 commit 7cac59d08a73cb866ec51a483a6f3fe0f531947c upstream. Prevent a crash from happening as the first serial port is initialised: Console: switching to mono frame buffer device 160x64 fb0: PMAG-AA frame buffer device at tc0 DECstation Z85C30 serial driver version 0.10 CPU 0 Unable to handle kernel paging request at virtual address 0000002c, epc == 803ab00c, ra == 803aafe0 Oops[#1]: CPU: 0 PID: 1 Comm: swapper Not tainted 6.4.0-rc3-00031-g84a9582fd203-dirty #57 $ 0 : 00000000 10012c00 803aaeb0 00000000 $ 4 : 80e12f60 80e12f50 80e12f58 81000030 $ 8 : 00000000 805ff37c 00000000 33433538 $12 : 65732030 00000006 80c2915d 6c616972 $16 : 80e12f00 807b7630 00000000 00000000 $20 : 00000004 00000348 000001a0 807623b8 $24 : 00000018 00000000 $28 : 80c24000 80c25d60 8078b148 803aafe0 Hi : 00000000 Lo : 00000000 epc : 803ab00c serial_base_ctrl_add+0x78/0xf4 ra : 803aafe0 serial_base_ctrl_add+0x4c/0xf4 Status: 10012c03 KERNEL EXL IE Cause : 00000008 (ExcCode 02) BadVA : 0000002c PrId : 00000440 (R4400SC) Modules linked in: Process swapper (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000) Stack : 80760000 00000cc0 00400044 00400040 803aa02c 80d61ab8 00000000 807b7630 80760000 807623b8 807b7628 803aa644 80386998 00000000 80e17780 80220f68 80e17780 80d61ab8 80c17d80 80e17780 80e17780 8063c798 80e17780 80383fa0 00000010 80e17780 00000000 80386998 807a0000 00000000 00400040 8038f848 807623b8 80d61ab8 00000004 80e17780 00000000 803a68e4 80c25e2c 803bb884 ... Call Trace: [<803ab00c>] serial_base_ctrl_add+0x78/0xf4 [<803aa644>] serial_core_register_port+0x174/0x69c [<8077e9ac>] zs_init+0xc8/0xfc [<800404d4>] do_one_initcall+0x40/0x2ac [<8076cecc>] kernel_init_freeable+0x1e4/0x270 [<80605bec>] kernel_init+0x20/0x108 [<800431e8>] ret_from_kernel_thread+0x14/0x1c Code: 2442aeb0 ae120024 ae0200d0 <8c67002c> 50e00001 8c670000 3c06806e 3c05806e afb30010 ---[ end trace 0000000000000000 ]--- (report at the offending commit) -- where a pointer is dereferenced that has been derived from a null pointer to the port's parent device. Since no device is available with legacy probing and it's not anymore a preferable way to discover devices anyway, switch the driver to using a platform device and use it as the port's parent device. Update resource handling accordingly and only request the actual span of addresses used within the slot, which will have had its resource already requested by generic platform device code. Use platform_driver_probe() not just because SCC devices are fixed with solder on board and not straightforward to remove, but foremost because the associated TTY's major device number is the same as used by the dz driver and the first driver to claim it will prevent the other one from using it. Either one DZ device or some SCC devices will be present in a given system but never both at a time, and therefore we want the major device number to be claimed by the first driver to actually successfully bind to its device and platform_driver_probe() is a way to fulfil that. An unfortunate consequence of the switch to a platform device is we now hand the console over from the bootconsole much later in the bootstrap. The firmware console handler appears good enough though to work so late and in particular with interrupts enabled. Since there is one way only remaining to reach zs_reset() now, remove the port initialisation marker as no longer needed and go through the channel reset unconditionally. Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM") Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Cc: stable@vger.kernel.org # needs to use .remove_new for <= 6.10 Link: https://patch.msgid.link/alpine.DEB.2.21.2605062328480.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 7cac59d08a73cb866ec51a483a6f3fe0f531947c upstream.

Prevent a crash from happening as the first serial port is initialised:

  Console: switching to mono frame buffer device 160x64
  fb0: PMAG-AA frame buffer device at tc0
  DECstation Z85C30 serial driver version 0.10
  CPU 0 Unable to handle kernel paging request at virtual address 0000002c, epc == 803ab00c, ra == 803aafe0
  Oops[#1]:
  CPU: 0 PID: 1 Comm: swapper Not tainted 6.4.0-rc3-00031-g84a9582fd203-dirty #57
  $ 0   : 00000000 10012c00 803aaeb0 00000000
  $ 4   : 80e12f60 80e12f50 80e12f58 81000030
  $ 8   : 00000000 805ff37c 00000000 33433538
  $12   : 65732030 00000006 80c2915d 6c616972
  $16   : 80e12f00 807b7630 00000000 00000000
  $20   : 00000004 00000348 000001a0 807623b8
  $24   : 00000018 00000000
  $28   : 80c24000 80c25d60 8078b148 803aafe0
  Hi    : 00000000
  Lo    : 00000000
  epc   : 803ab00c serial_base_ctrl_add+0x78/0xf4
  ra    : 803aafe0 serial_base_ctrl_add+0x4c/0xf4
  Status: 10012c03	KERNEL EXL IE
  Cause : 00000008 (ExcCode 02)
  BadVA : 0000002c
  PrId  : 00000440 (R4400SC)
  Modules linked in:
  Process swapper (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000)
  Stack : 80760000 00000cc0 00400044 00400040 803aa02c 80d61ab8 00000000 807b7630
          80760000 807623b8 807b7628 803aa644 80386998 00000000 80e17780 80220f68
          80e17780 80d61ab8 80c17d80 80e17780 80e17780 8063c798 80e17780 80383fa0
          00000010 80e17780 00000000 80386998 807a0000 00000000 00400040 8038f848
          807623b8 80d61ab8 00000004 80e17780 00000000 803a68e4 80c25e2c 803bb884
          ...
  Call Trace:
  [<803ab00c>] serial_base_ctrl_add+0x78/0xf4
  [<803aa644>] serial_core_register_port+0x174/0x69c
  [<8077e9ac>] zs_init+0xc8/0xfc
  [<800404d4>] do_one_initcall+0x40/0x2ac
  [<8076cecc>] kernel_init_freeable+0x1e4/0x270
  [<80605bec>] kernel_init+0x20/0x108
  [<800431e8>] ret_from_kernel_thread+0x14/0x1c

  Code: 2442aeb0  ae120024  ae0200d0 <8c67002c> 50e00001  8c670000  3c06806e  3c05806e  afb30010

  ---[ end trace 0000000000000000 ]---

(report at the offending commit) -- where a pointer is dereferenced that
has been derived from a null pointer to the port's parent device.

Since no device is available with legacy probing and it's not anymore a
preferable way to discover devices anyway, switch the driver to using a
platform device and use it as the port's parent device.  Update resource
handling accordingly and only request the actual span of addresses used
within the slot, which will have had its resource already requested by
generic platform device code.

Use platform_driver_probe() not just because SCC devices are fixed with
solder on board and not straightforward to remove, but foremost because
the associated TTY's major device number is the same as used by the dz
driver and the first driver to claim it will prevent the other one from
using it.  Either one DZ device or some SCC devices will be present in a
given system but never both at a time, and therefore we want the major
device number to be claimed by the first driver to actually successfully
bind to its device and platform_driver_probe() is a way to fulfil that.

An unfortunate consequence of the switch to a platform device is we now
hand the console over from the bootconsole much later in the bootstrap.
The firmware console handler appears good enough though to work so late
and in particular with interrupts enabled.

Since there is one way only remaining to reach zs_reset() now, remove
the port initialisation marker as no longer needed and go through the
channel reset unconditionally.

Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # needs to use .remove_new for <= 6.10
Link: https://patch.msgid.link/alpine.DEB.2.21.2605062328480.46195@angie.orcam.me.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
serial: zs: Switch to using channel reset 2026-06-09T10:28:49+00:00 Maciej W. Rozycki macro@orcam.me.uk 2026-05-06T22:42:43+00:00 81984447eac41d0807107234652d9ef28e7a07cc commit 8572955630f30948837088aa98bcbe0532d1ceac upstream. Switch the driver to using the channel reset rather than hardware reset, simplifying handling by removing an interference between channels that causes the other channel to become uninitialised afterwards. There is little difference between the two kinds of reset in terms of register settings that result, and we initialise the whole register set right away anyway. However this prevents a hang from happening should the console output handler in the firmware try to access the other port whose transmitter has been disabled and line parameters messed up. For example this will happen if the keyboard port (port A) is chosen for the system console, unusually but not insanely for a headless system, as the port is wired to a standard DA-15 connector and an adapter can be easily made. Or with the next change in place this would happen for the regular console port (port B), since the keyboard port (port A) will be initialised first. Just remove the unnecessary complication then, a channel reset is good enough. We still need the initialisation marker, now per channel rather than per SCC, as for the console port zs_reset() will be called twice: once early on via zs_serial_console_init() for the console setup only, and then again via zs_config_port() as the port is associated with a TTY device. Fixes: 8b4a40809e53 ("zs: move to the serial subsystem") Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Cc: stable@vger.kernel.org # v2.6.23+ Link: https://patch.msgid.link/alpine.DEB.2.21.2605062323430.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 8572955630f30948837088aa98bcbe0532d1ceac upstream.

Switch the driver to using the channel reset rather than hardware reset,
simplifying handling by removing an interference between channels that
causes the other channel to become uninitialised afterwards.

There is little difference between the two kinds of reset in terms of
register settings that result, and we initialise the whole register set
right away anyway.  However this prevents a hang from happening should
the console output handler in the firmware try to access the other port
whose transmitter has been disabled and line parameters messed up.

For example this will happen if the keyboard port (port A) is chosen for
the system console, unusually but not insanely for a headless system, as
the port is wired to a standard DA-15 connector and an adapter can be
easily made.  Or with the next change in place this would happen for the
regular console port (port B), since the keyboard port (port A) will be
initialised first.

Just remove the unnecessary complication then, a channel reset is good
enough.  We still need the initialisation marker, now per channel rather
than per SCC, as for the console port zs_reset() will be called twice:
once early on via zs_serial_console_init() for the console setup only,
and then again via zs_config_port() as the port is associated with a TTY
device.

Fixes: 8b4a40809e53 ("zs: move to the serial subsystem")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v2.6.23+
Link: https://patch.msgid.link/alpine.DEB.2.21.2605062323430.46195@angie.orcam.me.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>