fix(kernel/rockchip64-7.0): restore SysRq-via-BREAK on dw-apb-uart (8250_dw) by iav · Pull Request #9750 · armbian/build

iav · 2026-05-03T04:47:40Z

Summary

Restore SysRq-via-BREAK on dw-apb-uart (8250_dw) for linux-7.0.y kernels (RK3399 / helios64 and other rockchip64-7.0 boards).
The regression was introduced upstream in 8324a54f604d "serial: 8250: Add serial8250_handle_irq_locked()" (PATCH v2 4/7) and 883c5a2bc934 "serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling" (PATCH v2 5/7) by Ilpo Järvinen, both in the tty-7.0-rc5 pull (merge d46d5c838344); they replaced the explicit uart_unlock_and_check_sysrq_irqrestore() call with a guard(uart_port_lock_irqsave) scope. The guard releases the port lock at scope exit but never checks port->sysrq_ch, so handle_sysrq() is no longer called.
Other 8250-family drivers (amba-pl011, meson_uart, msm_serial, …) call uart_unlock_and_check_sysrq() explicitly; 8250_dw relied on serial8250_handle_irq() doing it for it. The fix restores that call on both paths.
The first commit was Cc: stable, so the regression also reaches v6.19.10 in the 6.19.y series.
Touches only patch/kernel/archive/rockchip64-7.0/ — no build-framework or extension changes.

Test plan

Verified on helios64 (RK3399, dw-apb-uart, ttyS2 @ 1.5 Mbaud, kernel 7.0.3-edge-rockchip64): on the picocom serial console, C-a C-\ (BREAK) followed by h produces sysrq: HELP : … from the kernel.
Reviewers welcome to test on other rockchip64-7.0 boards using dw-apb-uart.

Summary by CodeRabbit

Bug Fixes
- Fixed a regression preventing UART BREAK and SysRq character handling on dw-apb-uart devices in Linux 7.0.

…250_dw) Sending a serial BREAK followed by a SysRq command character stopped working on dw-apb-uart (e.g. RK3399 / helios64) in linux-7.0.y. The refactor that introduced the regression replaced the explicit uart_unlock_and_check_sysrq_irqrestore() in serial8250_handle_irq() with a guard(uart_port_lock_irqsave) scope. The guard releases the port lock at scope exit, but does NOT check port->sysrq_ch and therefore never calls handle_sysrq(). Other 8250-family drivers (amba-pl011, meson_uart, msm_serial, ...) each call uart_unlock_and_check_sysrq() explicitly in their IRQ handler; 8250_dw relied on serial8250_handle_irq() doing it for it. Fix: in dw8250_handle_irq() replace the guard() with explicit uart_port_lock_irqsave() + uart_unlock_and_check_sysrq_irqrestore() on the normal exit path; early-exit paths (UART_IIR_NO_INT / UART_IIR_BUSY) get plain uart_port_unlock_irqrestore() since they do not process RX chars. The same fix is applied to serial8250_handle_irq() as defence-in-depth for any other caller that goes through it. Verified on helios64 (RK3399, dw-apb-uart, ttyS2 @ 1.5 Mbaud): BREAK + 'h' on the picocom serial console produces the expected 'sysrq: HELP : ...' line from the kernel. Assisted-by: Claude:claude-opus-4-7

coderabbitai · 2026-05-03T04:47:47Z

No actionable comments were generated in the recent review. 🎉

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patch/kernel/archive/rockchip64-7.0/general-serial-8250-fix-sysrq-break-dw-apb.patch

📝 Walkthrough

Walkthrough

This patch fixes a SysRq BREAK handling regression in Linux 7.0's dw-apb-uart driver by refactoring IRQ handler locking patterns. Two functions now use explicit uart_port_lock_irqsave() and uart_unlock_and_check_sysrq_irqrestore() calls instead of scope-based guards to properly restore SysRq processing after handling interrupts.

Changes

SysRq BREAK Handling Fix in UART IRQ Handlers

Layer / File(s)	Summary
Explicit Lock Acquisition `patch/kernel/archive/rockchip64-7.0/general-serial-8250-fix-sysrq-break-dw-apb.patch`	Both `dw8250_handle_irq()` and `serial8250_handle_irq()` replace `guard(uart_port_lock_irqsave)` scope guards with explicit `uart_port_lock_irqsave(port, &flags)` calls to enable precise control over unlock points.
Early Return Path Fixes `patch/kernel/archive/rockchip64-7.0/general-serial-8250-fix-sysrq-break-dw-apb.patch`	`dw8250_handle_irq()` adds explicit `uart_port_unlock_irqrestore()` calls on early exits (no interrupt, BUSY status) to ensure locks are released before returning.
SysRq Restoration on Unlock `patch/kernel/archive/rockchip64-7.0/general-serial-8250-fix-sysrq-break-dw-apb.patch`	Both functions call `uart_unlock_and_check_sysrq_irqrestore()` at their normal exit paths after invoking `serial8250_handle_irq_locked()` to defer SysRq processing until lock release.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

🐰 A BREAK came through the serial line so fine,
SysRq whispered secrets, but lost the time.
With locks now explicit, and unlocks so clear,
The magic of checking returns, crystal near!
No more guard scope ghosts—just straightforward sight,
The dw-apb spins true, SysRq's alight! 🎯✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the main change: restoring SysRq-via-BREAK functionality on dw-apb-uart devices for the rockchip64-7.0 kernel.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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github-actions · 2026-05-04T19:25:31Z

✅ This PR has been reviewed and approved — all set for merge!

The mvebu kernel uses the same dw-apb-uart driver (drivers/tty/serial/8250/8250_dw.c) on Armada 388 / 38x SoCs as RK3399 does, and inherits the same SysRq-via-BREAK regression introduced by the guard(uart_port_lock_irqsave) refactor that PR #9750 fixes for kernel-rockchip64-7.0. Verified on helios4 (Armada 388, kernel-mvebu 6.18-edge) 2026-05-05: - Without patch: BREAK + 'h' through picocom is consumed by the IRQ handler (port->sysrq_ch is latched correctly), but uart_unlock_and_check_sysrq_irqrestore() is never called from the handler tail, so handle_sysrq() never runs. - With patch: BREAK + 'h' produces 'sysrq: HELP : ...' on the serial console (after raising console_loglevel above the boot-default 1). - Diagnostic trace_printk patch (local userpatches, not part of this PR) confirmed that has_sysrq=1, sysrq_armed=jiffies+5HZ after BREAK, sysrq_ch=104 ('h'=0x68) after the next char — i.e. all preconditions for handle_sysrq() are met, the only thing missing was the call site, which this patch restores. This is a verbatim copy of the rockchip64-7.0 patch (PR #9750) into patch/kernel/archive/mvebu-6.18/. Hunk context matches, applies cleanly. Per-board impact is identical to the original PR #9750: any mvebu board whose serial console is dw-apb-uart-derived (Armada 38x family — helios4, espressobin, clearfog, etc.) gets working sysrq via BREAK back. Companion to PR #9750 (rockchip64-7.0). No upstream submission planned (per maintainer decision in #9750 thread). Assisted-by: Claude:claude-opus-4.7 Signed-off-by: Igor Velkov <325961+iav@users.noreply.github.com>

iav requested review from ColorfulRhino, HeyMeco, JohnTheCoolingFan, SuperKali, TheSnowfield, Tonymac32, ahoneybun, amazingfate, brentr, catalinii, chainsx, efectn, igorpecovnik, joekhoobyar, krachlatte, lanefu, paolosabatino, prahal, pyavitz, rpardini and schwar3kat as code owners May 3, 2026 04:47

github-actions Bot added 05 Milestone: Second quarter release size/medium PR with more then 50 and less then 250 lines Needs review Seeking for review Hardware Hardware related like kernel, U-Boot, ... Patches Patches related to kernel, U-Boot, ... labels May 3, 2026

igorpecovnik approved these changes May 4, 2026

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github-actions Bot added the Ready to merge Reviewed, tested and ready for merge label May 4, 2026

github-actions Bot removed the Needs review Seeking for review label May 4, 2026

iav mentioned this pull request May 4, 2026

fix(kernel/mvebu-6.18): restore SysRq-via-BREAK on dw-apb-uart (8250_dw) #9760

Merged

igorpecovnik merged commit ad8f89d into armbian:main May 5, 2026
12 checks passed

iav deleted the fix/sysrq-break-dw8250 branch May 5, 2026 15:03

This was referenced May 7, 2026

feat(extensions): sysrq-serial-trigger + kernel-debug-tiers (on-device kernel debugging via serial console) #9775

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feat(extensions): sysrq-serial-trigger + kernel-debug-tiers (on-device kernel debugging via serial console) #9776

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fix(kernel/rockchip64-7.0): restore SysRq-via-BREAK on dw-apb-uart (8250_dw)#9750

fix(kernel/rockchip64-7.0): restore SysRq-via-BREAK on dw-apb-uart (8250_dw)#9750
igorpecovnik merged 1 commit intoarmbian:mainfrom
iav:fix/sysrq-break-dw8250

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