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impostorscore=0 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605100145 From: Ionut Nechita Hi Greg, Ilpo, This series backports the 8250_dw BUSY deassert fix to 6.12.y, per Ilpo's guidance from the request thread: https://lore.kernel.org/linux-serial/deb9499d-3245-7e38-9034-e533d4b5f512@linux.intel.com/ Background: we ship 6.12 LTS as part of a certified production platform (StarlingX/Yocto) and are hitting the BUSY assertion issue on Intel DesignWare 8250 UARTs - LCR writes get silently ignored under Rx load, causing baud-rate / framing mismatches after set_termios. A major LTS bump is a multi-month re-qualification we can't justify for a single subsystem fix. The original mainline series is 7 patches by Ilpo (plus its dependencies). For 6.12.y, the resulting series here is 8 patches: Prerequisites (per Ilpo): 1/8 serial: 8250: use serial_port_in/out() helpers [dbd26a886e94] 2/8 serial: 8250_dw: Comment possible corner cases ... [bd8cad85561b] BUSY deassert series: 3/8 serial: 8250: Protect LCR write in shutdown [59a33d83bbe6] 4/8 serial: 8250_dw: Avoid unnecessary LCR writes [8002d6d6d0d8] 5/8 serial: 8250: Add serial8250_handle_irq_locked() [8324a54f604d] 6/8 serial: 8250_dw: Rework dw8250_handle_irq() ... [883c5a2bc934] 7/8 serial: 8250_dw: Rework IIR_NO_INT handling ... [73a4ed8f9efa] 8/8 serial: 8250_dw: Ensure BUSY is deasserted [a7b9ce39fbe4] Notes: - Patch 6/7 of the original mainline series, commit e0a368ae7953 ("serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY"), is *already* in 6.12.y as commit 0bae1c670aa8 ("serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY") (Ilpo, 2026-02-03), so it is not re-sent here. Functionally this means patches 3-8 above land on top of the existing late-synchronize_irq() fix; the conflict in patch 3 (LCR write placement around the late synchronize_irq) was resolved accordingly. - Ilpo's other suggested prerequisites are *not* included as prereqs: * commit b339809edda1 ("serial: 8250: use guard()s") * commit fc9ceb501e38 ("serial: 8250: sanitize uart_port::serial_{in,out}() types") * commit c213375e3283 ("serial: 8250_dw: Call dw8250_quirks() conditionally") Reasoning: * commit b339809edda1 ("serial: 8250: use guard()s") is a large refactor and only the shutdown hunk was needed; instead, patches 3, 5, 6, 7 here are adapted to use the existing explicit uart_port_lock_irqsave/unlock_irqrestore form rather than the cleanup-based guard() introduced by that commit; * commit fc9ceb501e38 ("serial: 8250: sanitize uart_port::serial_{in,out}() types") only causes a trivial conflict in patch 8 in code that the BUSY change removes anyway (per Ilpo's note); * commit c213375e3283 ("serial: 8250_dw: Call dw8250_quirks() conditionally") only causes a conflict in patch 7 around the dw8250_setup_dma_filter() helper and the conditional p->handle_irq assignment, neither of which exist in 6.12.y and neither of which is needed for the BUSY fix. - Namespace export syntax: in 6.12.y both EXPORT_SYMBOL_NS_GPL() and MODULE_IMPORT_NS() apply __stringify(ns) to the namespace argument, so it must be a bare identifier. Mainline (where the upstream patches were written) accepts a string literal. Patches 5 and 8 here use the bare-identifier form (SERIAL_8250) instead of the upstream string form ("SERIAL_8250"); without this fix the .vmlinux.export.c link step fails with "expected ':' or ')' before 'SERIAL_8250'". This is noted in the [Ionut: ...] block of the affected patches. Each of patches 3, 5, 6, 7 and 8 carries an explicit "[Ionut: adapt to 6.12.y - ...]" note describing exactly what was changed relative to the upstream commit. Build: - Each patch builds individually on 6.12.87 to a complete vmlinux (bisect-safe), with CONFIG_SERIAL_8250=y, CONFIG_SERIAL_8250_DW=m on x86_64 defconfig. Testing plan: - We will test on Intel platforms with DW APB UART (snps,dw-apb-uart) running 6.12.57-rt / 6.12.87-rt (PREEMPT_RT) to confirm the original symptom (LCR writes silently ignored under Rx load -> baud / framing mismatch after set_termios) is gone. Will report Tested-by once cycles complete. Based on: linux-6.12.y at v6.12.87 (8bf2f55ef536). Andy Shevchenko (1): serial: 8250_dw: Comment possible corner cases in serial_out() implementation Ilpo Järvinen (6): serial: 8250: Protect LCR write in shutdown serial: 8250_dw: Avoid unnecessary LCR writes serial: 8250: Add serial8250_handle_irq_locked() serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm serial: 8250_dw: Ensure BUSY is deasserted Jiri Slaby (SUSE) (1): serial: 8250: use serial_port_in/out() helpers drivers/tty/serial/8250/8250.h | 25 +++ drivers/tty/serial/8250/8250_dw.c | 298 +++++++++++++++++++++++----- drivers/tty/serial/8250/8250_fsl.c | 8 +- drivers/tty/serial/8250/8250_omap.c | 2 +- drivers/tty/serial/8250/8250_port.c | 66 +++--- include/linux/serial_8250.h | 1 + 6 files changed, 319 insertions(+), 81 deletions(-) -- 2.54.0