kernel/linux.git/drivers/tty/pty.c, branch v7.1-rc5

tty: tty_port: add workqueue to flip TTY buffer

2026-03-12T14:26:29+00:00

On the embedded platform, certain critical data, such as IMU data, is transmitted through UART. The tty_flip_buffer_push() interface in the TTY layer uses system_dfl_wq to handle the flipping of the TTY buffer. Although the unbound workqueue can create new threads on demand and wake up the kworker thread on an idle CPU, it may be preempted by real-time tasks or other high-prio tasks. flush_to_ldisc() needs to wake up the relevant data handle thread. When executing __wake_up_common_lock(), it calls spin_lock_irqsave(), which does not disable preemption but disables migration in RT-Linux. This prevents the kworker thread from being migrated to other cores by CPU's balancing logic, resulting in long delays. The call trace is as follows: __wake_up_common_lock __wake_up ep_poll_callback __wake_up_common __wake_up_common_lock __wake_up n_tty_receive_buf_common n_tty_receive_buf2 tty_ldisc_receive_buf tty_port_default_receive_buf flush_to_ldisc In our system, the processing interval for each frame of IMU data transmitted via UART can experience significant jitter due to this issue. Instead of the expected 10 to 15 ms frame processing interval, we see spikes up to 30 to 35 ms. Moreover, in just one or two hours, there can be 2 to 3 occurrences of such high jitter, which is quite frequent. This jitter exceeds the software's tolerable limit of 20 ms. Introduce flip_wq in tty_port which can be set by tty_port_link_wq() or as default linked to default workqueue allocated when tty_register_driver(). The default workqueue is allocated with flag WQ_SYSFS, so that cpumask and nice can be set dynamically. The execution timing of tty_port_link_wq() is not clearly restricted. The newly added function tty_port_link_driver_wq() checks whether the flip_wq of the tty_port has already been assigned when linking the default tty_driver's workqueue to the port. After the user has set a custom workqueue for a certain tty_port using tty_port_link_wq(), the system will only use this custom workqueue, even if tty_driver does not have %TTY_DRIVER_NO_WORKQUEUE flag. When tty_port register device, flip_wq link operation is done by tty_port_link_driver_wq(), but for in-memory devices the link operation cannot cover all the cases. Although tty_port_install() is dedicated for in-memory devices lik PTY to link port allocated on demand, the logic of tty_port_install() is so simple that people may not call it, vc_cons[0].d->port is one such case. We check the buf.flip_wq when flip TTY buffer, if buf.flip_wq of TTY port is NULL, use system_dfl_wq as a backup. To avoid naming conflict of the default tty_driver's workqueue, using '"%s-%s", driver->name, driver->driver_name' as the workqueue name. In cases where driver_name is not specified and therefore is NULL, the workqueue is not created. Drivers that do not define driver_name are potentially in-memory devices like vty, which generally do not require special workqueue settings. Even with the combination of name and driver_name, the workqueue names can still be duplicated, as many tty serial drivers use "ttyS" as dev_name and "serial" as driver_name. I modified the conflicting driver_name of these drivers by appending a suffix of _xx based on the corresponding .c file. If this modification is not made, it could not only lead to duplicate workqueue names but also result in duplicate entries for the /proc/tty/driver/ nodes. Introduce %TTY_DRIVER_NO_WORKQUEUE flag meaning not to create the default single tty_driver workqueue. Two reasons why need to introduce the %TTY_DRIVER_NO_WORKQUEUE flag: 1. If the WQ_SYSFS parameter is enabled, workqueue_sysfs_register() will fail when trying to create a workqueue with the same name. The pty is an example of this; if both CONFIG_LEGACY_PTYS and CONFIG_UNIX98_PTYS are enabled, the call to tty_register_driver() in unix98_pty_init() will fail. 2. Different TTY ports may be used for different tasks, which may require separate core binding control via workqueues. In this case, the workqueue created by default in the TTY driver is unnecessary. Enabling this flag prevents the creation of this redundant workqueue. After applying this patch, we can set the related UART TTY flip buffer workqueue by sysfs. We set the cpumask to CPU cores associated with the IMU tasks, and set the nice to -20. Testing has shown significant improvement in the previously described issue, with almost no stuttering occurring anymore. Tested-by: Tommaso Merciai Tested-by: Marek Szyprowski Signed-off-by: Xin Zhao Link: https://patch.msgid.link/20260213085039.3274704-1-jackzxcui1989@163.com Signed-off-by: Greg Kroah-Hartman

Convert 'alloc_obj' family to use the new default GFP_KERNEL argument

2026-02-22T01:09:51+00:00

This was done entirely with mindless brute force, using git grep -l '\

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook

Merge tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2025-12-07T02:38:19+00:00

Pull tty/serial updates from Greg KH: "Here is the big set of tty/serial driver changes for 6.19-rc1. Nothing major at all, just small constant churn to make the tty layer "cleaner" as well as serial driver updates and even a new test added! Included in here are: - More tty/serial cleanups from Jiri - tty tiocsti test added to hopefully ensure we don't regress in this area again - sc16is7xx driver updates - imx serial driver updates - 8250 driver updates - new hardware device ids added - other minor serial/tty driver cleanups and tweaks All of these have been in linux-next for a while with no reported issues" * tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (60 commits) serial: sh-sci: Fix deadlock during RSCI FIFO overrun error dt-bindings: serial: rsci: Drop "uart-has-rtscts: false" LoongArch: dts: Add uart new compatible string serial: 8250: Add Loongson uart driver support dt-bindings: serial: 8250: Add Loongson uart compatible serial: 8250: add driver for KEBA UART serial: Keep rs485 settings for devices without firmware node serial: qcom-geni: Enable Serial on SA8255p Qualcomm platforms serial: qcom-geni: Enable PM runtime for serial driver serial: sprd: Return -EPROBE_DEFER when uart clock is not ready tty: serial: samsung: Declare earlycon for Exynos850 serial: icom: Convert PCIBIOS_* return codes to errnos serial: 8250-of: Fix style issues in 8250_of.c serial: add support of CPCI cards serial: mux: Fix kernel doc for mux_poll() tty: replace use of system_unbound_wq with system_dfl_wq serial: 8250_platform: simplify IRQF_SHARED handling serial: 8250: make share_irqs local to 8250_platform serial: 8250: move skip_txen_test to core serial: drop SERIAL_8250_DEPRECATED_OPTIONS ...

tty: convert ptm_open_peer() to FD_ADD()

2025-11-28T11:42:36+00:00

Christian Brauner says: The fix sent in [1] was squashed into this commit. Fixes: https://lore.kernel.org/37ac7af5-584f-4768-a462-4d1071c43eaf@sirena.org.uk [1] Reported-by: Mark Brown [1] Suggested-by: Linus Torvalds [1] Link: https://patch.msgid.link/20251123-work-fd-prepare-v4-42-b6efa1706cfd@kernel.org Signed-off-by: Christian Brauner

tty: pty: use guard()s

2025-11-21T17:30:39+00:00

Use guards in the pty code. This improves readability, makes error handling easier, and marks locked portions of code explicit. All that while being sure the lock is unlocked. pty_set_pktmode() is handled specially -- the conditions are inverted and return called if conditions unmet. This avoid double nested 'if's. The variable is renamed to want_pktmode so it is not confused with the current state of pktmode. Signed-off-by: Jiri Slaby (SUSE) Link: https://patch.msgid.link/20251119100140.830761-2-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

fsnotify: use accessor to set FMODE_NONOTIFY_*

2025-02-07T09:27:26+00:00

The FMODE_NONOTIFY_* bits are a 2-bits mode. Open coding manipulation of those bits is risky. Use an accessor file_set_fsnotify_mode() to set the mode. Rename file_set_fsnotify_mode() => file_set_fsnotify_mode_from_watchers() to make way for the simple accessor name. Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20250203223205.861346-2-amir73il@gmail.com Signed-off-by: Christian Brauner

tty: make tty_operations::write()'s count size_t

2023-08-11T19:12:46+00:00

Unify with the rest of the code. Use size_t for counts and ssize_t for retval. Signed-off-by: "Jiri Slaby (SUSE)" Link: https://lore.kernel.org/r/20230810091510.13006-30-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: propagate u8 data to tty_operations::write()

2023-08-11T19:12:46+00:00

Data are now typed as u8. Propagate this change to tty_operations::write(). Signed-off-by: "Jiri Slaby (SUSE)" Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Matt Turner Cc: Geert Uytterhoeven Cc: Richard Weinberger Cc: Anton Ivanov Cc: Johannes Berg Cc: Chris Zankel Cc: Max Filippov Cc: Arnd Bergmann Cc: Vaibhav Gupta Cc: Jens Taprogge Cc: Karsten Keil Cc: Scott Branden Cc: Ulf Hansson Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Alexander Gordeev Cc: Christian Borntraeger Cc: Sven Schnelle Cc: David Lin Cc: Johan Hovold Cc: Alex Elder Cc: Laurentiu Tudor Cc: Jiri Kosina Cc: David Sterba Cc: Shawn Guo Cc: Sascha Hauer Cc: Pengutronix Kernel Team Cc: Fabio Estevam Cc: NXP Linux Team Cc: Arnaud Pouliquen Cc: Oliver Neukum Cc: Mathias Nyman Cc: Marcel Holtmann Cc: Johan Hedberg Cc: Luiz Augusto von Dentz Link: https://lore.kernel.org/r/20230810091510.13006-28-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: make tty_class a static const structure

2023-04-03T19:43:07+00:00

Now that the driver core allows for struct class to be in read-only memory, move the tty_class structure to be declared at build time placing it into read-only memory, instead of having to be dynamically allocated at boot time. Cc: "Ilpo Järvinen" Reviewed-by: Jiri Slaby Link: https://lore.kernel.org/r/2023040250-landowner-unfitted-11f4@gregkh Signed-off-by: Greg Kroah-Hartman