kernel/linux.git/drivers/tty, branch v7.1-rc6

serial: dz: Enable modular build

2026-05-22T09:52:34+00:00

Enable modular build since the driver now has a proper module_exit() handler. There's nothing specific to DZ hardware to prevent driver unloading and reloading from working. Signed-off-by: Maciej W. Rozycki Link: https://patch.msgid.link/alpine.DEB.2.21.2605062331420.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman

serial: zs: Convert to use a platform device

2026-05-22T09:52:34+00:00

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 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

serial: dz: Convert to use a platform device

2026-05-22T09:52:34+00:00

Prevent a crash from happening as the first serial port is initialised: Console: switching to colour frame buffer device 160x64 tgafb: SFB+ detected, rev=0x02 fb0: Digital ZLX-E1 frame buffer device at 0x1e000000 DECstation DZ serial driver version 1.04 CPU 0 Unable to handle kernel paging request at virtual address 000000bc, epc == 8048b3a4, ra == 80470a78 Oops[#1]: CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0-dirty #35 NONE $ 0 : 00000000 1000ac00 00000004 804707ac $ 4 : 00000000 80e20850 80e20858 81000030 $ 8 : 00000000 8072c81c 00000008 fefefeff $12 : 6c616972 00000006 80c5917f 69726420 $16 : 80e20800 00000000 808f8968 80e20800 $20 : 00000000 807f5a90 808b0094 808d3bc8 $24 : 00000018 80479030 $28 : 80c2e000 80c2fd70 00000069 80470a78 Hi : 00000004 Lo : 00000000 epc : 8048b3a4 __dev_fwnode+0x0/0xc ra : 80470a78 serial_base_ctrl_add+0xa0/0x168 Status: 1000ac04 IEp Cause : 30000008 (ExcCode 02) BadVA : 000000bc PrId : 00000220 (R3000) Modules linked in: Process swapper/0 (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000) Stack : 00400044 00400040 8046f4cc 00000000 808a6148 808a0000 808f8968 8086983c 808e0000 8046fc84 1000ac01 00000028 80e20700 802ba3f8 80e20700 80d34a94 80c1b900 80e20700 80e20700 80e20700 80e20700 80444650 00000000 00000000 00000000 807f5a90 808b0094 80447080 00400040 808e0000 80d34a94 808a6148 80d34a94 00000004 80e20700 00000000 8076974c 80469810 80c2fe3c 1000ac01 ... Call Trace: [<8048b3a4>] __dev_fwnode+0x0/0xc [<80470a78>] serial_base_ctrl_add+0xa0/0x168 [<8046fc84>] serial_core_register_port+0x1c8/0x974 [<808c6af0>] dz_init+0x74/0xc8 [<800470e0>] do_one_initcall+0x44/0x2d4 [<808b111c>] kernel_init_freeable+0x258/0x308 [<8072e434>] kernel_init+0x20/0x114 [<80049cd0>] ret_from_kernel_thread+0x14/0x1c Code: 27bd0018 03e00008 2402ffea <8c8200bc> 03e00008 00000000 27bdffc0 afbe0038 afb30024 ---[ end trace 0000000000000000 ]--- -- 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 the DZ device is 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 zs 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. Conversely only starting the console port so late lets the reset code fully utilise our delay handlers, so switch from udelay() to fsleep() for transmitter draining so as to avoid busy-waiting for an excessive amount of time. Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM") Signed-off-by: Maciej W. Rozycki Cc: stable@vger.kernel.org # needs to use .remove_new for <= 6.10 Link: https://patch.msgid.link/alpine.DEB.2.21.2605062326540.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman

serial: zs: Switch to using channel reset

2026-05-22T09:52:34+00:00

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 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

serial: zs: Fix bootconsole handover lockup

2026-05-22T09:52:34+00:00

Calling zs_reset() in the course of setting up the serial device causes line parameters to be reset and the transmitter disabled. We've been lucky in that no message is usually produced to the kernel log between this call and the later call to uart_set_options() in the course of console setup done by zs_serial_console_init(), or the system would hang as the console output handler in the firmware tried to access a port the transmitter of which has been disabled and line parameters messed up. This will change with the next change to the driver, so fix zs_reset() such that line parameters are set for 9600n8 console operation as with the system firmware and the transmitter re-enabled after reset. This also means zs_pm() serves no purpose anymore, so drop it. Fixes: 8b4a40809e53 ("zs: move to the serial subsystem") Signed-off-by: Maciej W. Rozycki Cc: stable@vger.kernel.org # v2.6.23+ Link: https://patch.msgid.link/alpine.DEB.2.21.2605062308040.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman

serial: dz: Fix bootconsole handover lockup

2026-05-22T09:52:34+00:00

Calling dz_reset() in the course of setting up the serial device causes line parameters to be reset and the transmitter disabled. We've been lucky in that no message is usually produced to the kernel log between this call and the later call to uart_set_options() in the course of console setup done by dz_serial_console_init(), or the system would hang as the console output handler in the firmware tried to access a port the transmitter of which has been disabled and line parameters messed up. This will change with the next change to the driver, so fix dz_reset() such that line parameters are set for 9600n8 console operation as with the system firmware and the transmitter re-enabled after reset. This also means dz_pm() serves no purpose anymore, so drop it. Fixes: e6ee512f5a77 ("dz.c: Resource management") Signed-off-by: Maciej W. Rozycki Cc: stable@vger.kernel.org # v2.6.25+ Link: https://patch.msgid.link/alpine.DEB.2.21.2605062302010.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman

serial: dz: Fix bootconsole message clobbering at chip reset

2026-05-22T09:52:33+00:00

In the DZ interface as implemented by the DC7085 gate array the serial transmitters are double buffered, meaning that at the time a transmitter is ready to accept the next character there is one in the transmit shift register still being sent to the line. Issuing a master clear at this time causes this character to be lost, so wait an extra amount of time sufficient for the transmit shift register to drain at 9600bps, which is the baud rate setting used by the firmware console. Mind the specified 1.4us TRDY recovery time in the course and continue using iob() as the completion barrier, since the platforms involved use a write buffer that can delay and combine writes, and reorder them with respect to reads regardless of the MMIO locations accessed and we still lack a platform-independent handler for that. When called from dz_serial_console_init() this is too early for fsleep() to work and even before lpj has been calculated and therefore the delay is actually not sufficient for the transmitter to drain and is merely a placeholder now. This will be addressed in a follow-up change. Fixes: e6ee512f5a77 ("dz.c: Resource management") Signed-off-by: Maciej W. Rozycki Cc: stable@vger.kernel.org # v2.6.25+ Link: https://patch.msgid.link/alpine.DEB.2.21.2605062259080.46195@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman

serial: 8250_dw: dispatch SysRq character in dw8250_handle_irq()

2026-05-22T09:51:35+00:00

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 Signed-off-by: Jacques Nilo Link: https://patch.msgid.link/ed56fcaf4af24e4ed011a7bce206e0182acb761c.1778675349.git.jnilo@free.fr Signed-off-by: Greg Kroah-Hartman

serial: 8250: dispatch SysRq character in serial8250_handle_irq()

2026-05-22T09:51:35+00:00

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 Signed-off-by: Jacques Nilo Link: https://patch.msgid.link/52692ae6c3501f7940347cef364ad7fcacaab7e5.1778675349.git.jnilo@free.fr Signed-off-by: Greg Kroah-Hartman

tty: serial: samsung: Remove redundant port lock acquisition in rx helpers

2026-05-22T09:48:38+00:00

Sashiko identified a deadlock when the console flow is engaged [1]. When console flow control is enabled (UPF_CONS_FLOW), s3c24xx_serial_stop_tx() calls s3c24xx_serial_rx_enable() and s3c24xx_serial_start_tx() calls s3c24xx_serial_rx_disable(). The serial core framework invokes the .stop_tx() and .start_tx() callbacks with the port->lock spinlock already held. Furthermore, all internal driver paths that invoke stop_tx (such as the DMA TX completion handler s3c24xx_serial_tx_dma_complete() or the PIO TX IRQ handler s3c24xx_serial_tx_irq()) also acquire port->lock prior to calling it. (Note that s3c24xx_serial_start_tx() is only invoked by the serial core). However, s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable() unconditionally attempt to acquire port->lock again using uart_port_lock_irqsave(). Since spinlocks are not recursive, this causes a deadlock on the same CPU when console flow control is engaged. Remove the redundant lock acquisition from both rx helper functions. Cc: stable Fixes: b497549a035c ("[ARM] S3C24XX: Split serial driver into core and per-cpu drivers") Reported-by: John Ogness Closes: https://sashiko.dev/#/patchset/20260506121606.5805-1-john.ogness%40linutronix.de [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260515-samsung-tty-flow-control-deadlock-v1-1-93255edbc9bc@linaro.org Signed-off-by: Greg Kroah-Hartman