kernel/linux.git/Documentation/driver-api/serial, branch v6.1.168

serial: mctrl_gpio: split disable_ms into sync and no_sync APIs

2025-06-04T12:40:13+00:00

[ Upstream commit 1bd2aad57da95f7f2d2bb52f7ad15c0f4993a685 ] The following splat has been observed on a SAMA5D27 platform using atmel_serial: BUG: sleeping function called from invalid context at kernel/irq/manage.c:738 in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 27, name: kworker/u5:0 preempt_count: 1, expected: 0 INFO: lockdep is turned off. irq event stamp: 0 hardirqs last enabled at (0): [<00000000>] 0x0 hardirqs last disabled at (0): [] copy_process+0x1c4c/0x7bec softirqs last enabled at (0): [] copy_process+0x1ca0/0x7bec softirqs last disabled at (0): [<00000000>] 0x0 CPU: 0 UID: 0 PID: 27 Comm: kworker/u5:0 Not tainted 6.13.0-rc7+ #74 Hardware name: Atmel SAMA5 Workqueue: hci0 hci_power_on [bluetooth] Call trace: unwind_backtrace from show_stack+0x18/0x1c show_stack from dump_stack_lvl+0x44/0x70 dump_stack_lvl from __might_resched+0x38c/0x598 __might_resched from disable_irq+0x1c/0x48 disable_irq from mctrl_gpio_disable_ms+0x74/0xc0 mctrl_gpio_disable_ms from atmel_disable_ms.part.0+0x80/0x1f4 atmel_disable_ms.part.0 from atmel_set_termios+0x764/0x11e8 atmel_set_termios from uart_change_line_settings+0x15c/0x994 uart_change_line_settings from uart_set_termios+0x2b0/0x668 uart_set_termios from tty_set_termios+0x600/0x8ec tty_set_termios from ttyport_set_flow_control+0x188/0x1e0 ttyport_set_flow_control from wilc_setup+0xd0/0x524 [hci_wilc] wilc_setup [hci_wilc] from hci_dev_open_sync+0x330/0x203c [bluetooth] hci_dev_open_sync [bluetooth] from hci_dev_do_open+0x40/0xb0 [bluetooth] hci_dev_do_open [bluetooth] from hci_power_on+0x12c/0x664 [bluetooth] hci_power_on [bluetooth] from process_one_work+0x998/0x1a38 process_one_work from worker_thread+0x6e0/0xfb4 worker_thread from kthread+0x3d4/0x484 kthread from ret_from_fork+0x14/0x28 This warning is emitted when trying to toggle, at the highest level, some flow control (with serdev_device_set_flow_control) in a device driver. At the lowest level, the atmel_serial driver is using serial_mctrl_gpio lib to enable/disable the corresponding IRQs accordingly. The warning emitted by CONFIG_DEBUG_ATOMIC_SLEEP is due to disable_irq (called in mctrl_gpio_disable_ms) being possibly called in some atomic context (some tty drivers perform modem lines configuration in regions protected by port lock). Split mctrl_gpio_disable_ms into two differents APIs, a non-blocking one and a blocking one. Replace mctrl_gpio_disable_ms calls with the relevant version depending on whether the call is protected by some port lock. Suggested-by: Jiri Slaby Signed-off-by: Alexis Lothoré Acked-by: Richard Genoud Link: https://lore.kernel.org/r/20250217-atomic_sleep_mctrl_serial_gpio-v3-1-59324b313eef@bootlin.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin

tty: serial: document uart_get_console()

2022-07-28T08:37:42+00:00

This was the only function mentioned in the text, but was neither linked nor documented. So document and link it, so that hyperlinking works in the text. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220728061056.20799-6-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

tty: serial: serial_core, reformat kernel-doc for functions

2022-07-28T08:37:42+00:00

There are many annotated functions in serial_core.c, but they do not completely conform to the kernel-doc style. So reformat them and link them from the Documentation. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220728061056.20799-5-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

Documentation: serial: link uart_ops properly

2022-07-28T08:37:42+00:00

The syntax to reference a struct in text is "struct XY". So reference uart_ops properly, so that hyperlinks work. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220728061056.20799-4-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

Documentation: serial: move GPIO kernel-doc to the functions

2022-07-28T08:37:42+00:00

The GPIO uart functions are documented in Documentation. Move and transform this documentation into kernel-doc directly in the code and reference it in Documentation using kernel-doc:. This makes it easier to update, maintain and check by the build. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220728061056.20799-3-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

Documentation: serial: dedup kernel-doc for uart functions

2022-07-28T08:37:42+00:00

Some of the serial (uart_*) functions are documented twice. Once as kernel-doc along their sources and once in Documentation. So deduplicate these texts, merge them into kernel-doc in the sources, and link them using kernel-doc: from the Documentation. To be properly linked and rendered, tabulators had to be removed from the comments. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220728061056.20799-2-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

Documentation: serial: move uart_ops documentation to the struct

2022-07-28T08:37:42+00:00

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 Link: https://lore.kernel.org/r/20220728061056.20799-1-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman

serial: Support for RS-485 multipoint addresses

2022-06-27T12:44:20+00:00

Add support for RS-485 multipoint addressing using 9th bit [*]. The addressing mode is configured through ->rs485_config(). ADDRB in termios indicates 9th bit addressing mode is enabled. In this mode, 9th bit is used to indicate an address (byte) within the communication line. ADDRB can only be enabled/disabled through ->rs485_config() that is also responsible for setting the destination and receiver (filter) addresses. Add traps to detect unwanted changes to struct serial_rs485 layout using static_assert(). [*] Technically, RS485 is just an electronic spec and does not itself specify the 9th bit addressing mode but 9th bit seems at least "semi-standard" way to do addressing with RS485. Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20220624204210.11112-6-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman

serial: Drop timeout from uart_port

2022-06-27T12:34:45+00:00

Since commit 31f6bd7fad3b ("serial: Store character timing information to uart_port"), per frame timing information is available on uart_port. Uart port's timeout can be derived from frame_time by multiplying with fifosize. Most callers of uart_poll_timeout are not made under port's lock. To be on the safe side, make sure frame_time is only accessed once. As fifo_size is effectively a constant, it shouldn't cause any issues. Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20220613113905.22962-1-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman

serial: Sanitize rs485_struct

2022-06-10T11:49:57+00:00

Sanitize serial_rs485 struct before calling into rs485_setup. The drivers provide supported_rs485 to help sanitization of the fields. If neither of SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND supported, don't pretend they can be set to sane settings but clear them both instead. If only one of them is supported it may look tempting to use the one driver supports to set the other, however, the userspace does not have that information readily available so it wouldn't be helpful. While adjusting the documentation, remove also the claim that TIOCGRS485 would call driver specific code. In reality, it does nothing else than copies the stored serial_rs485 structure from uart_port to userspace. Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20220606100433.13793-23-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman