On Sat, 24 Oct 2026, James Hilliard wrote: > Reserve canceled transmit and receive storage until DMA and its completion > callbacks have retired. Serial-core write backpressure protects a flushed > TX FIFO while normal transfers continue to DMA directly from that FIFO. > > The series separates OMAP's locked completion processing and serializes > asynchronous write wakeups with the port lock before adding the serial-core > reservation helpers and applying them to 8250 TX. Flushing > empties the logical queue immediately. While the old transfer owns its > storage, write_room() reports zero and write-ready notifications wait for > retirement. Failed termination retains the reservation until normal > completion, without advancing the reset FIFO. DMA retirement releases the > reservation independently of port readiness. Serial core keeps writes and > wakeups gated during shutdown until successful startup or resume. > > RX delivers paused data before the PIO fallback and retires callbacks in > process context. Track FIFO access separately from buffer retirement so > PIO and the DesignWare empty-FIFO timeout handling can run once DMA has > released the FIFO. On failure, retain the requested interrupt enables in > the existing IER shadow and mask receive interrupts in hardware until DMA > has stopped. Recovery then leaves RX on PIO until reopen. Shutdown excludes > new retirement work before releasing the channels. > > Based on tty-next with the posted shutdown guard [0], channel > configuration error handling [1], RX TTY accounting fix [2], RZ/N1 > transfer-length fix [3], transmit-PM shutdown fix [4], serport > write-wakeup deferral [5], DesignWare BUSY-safe fractional-divisor > programming [6], and Intel MID RX DMA timeout locking [7]. The serport fix > is needed before serializing the remaining write-wakeup callers with the > port lock. > > [0] > https://lore.kernel.org/r/20261021-submit-serial-8250-dma-shutdown-v1-v1-1-3d3ce383c...@gmail.com > [1] > https://lore.kernel.org/r/20261021-submit-serial-8250-dma-config-errors-v1-v1-1-c067587d1...@gmail.com > [2] > https://lore.kernel.org/r/20261021-submit-serial-8250-dma-rx-accounting-v1-v1-1-c11795914...@gmail.com > [3] > https://lore.kernel.org/r/20261023-submit-serial-8250-dma-tx-length-v1-v2-1-c3106ef4d...@gmail.com > [4] > https://lore.kernel.org/r/20261022-submit-serial-8250-tx-pm-shutdown-v1-v1-1-0e894afa3...@gmail.com > [5] > https://lore.kernel.org/r/20261023-submit-serport-write-wakeup-v1-v1-1-74e731163...@gmail.com > [6] > https://lore.kernel.org/r/20261024-submit-serial-8250-dw-divisor-v1-v2-1-032ca5338...@gmail.com > [7] > https://lore.kernel.org/r/20261024-submit-serial-8250-mid-rx-lock-v1-v1-1-2b9afdf86...@gmail.com > > Assisted-by: Codex:gpt-6-astra > Signed-off-by: James Hilliard <[email protected]> > --- > Changes in v6:
Hi, This series is moving way too fast with new versions. Please slow down. We're not aiming to who manages to produce highest version counter for a series. ;-) You're making non-trivial changes so please do expect human review to take time. Cranking new versions almost back to back (or even every other day) will just fill up inboxes. -- i. > - Use v2 of the DesignWare BUSY-safe fractional-divisor prerequisite. > - Serialize CLPS711x TX servicing and interrupt-enable state with the > port lock. Use non-waiting IRQ disable in stop_tx(), skip queued TX > interrupts after stopping, and drain the handler outside the lock > during shutdown. > - Make the Atmel RX/TX tasklets and SB1250 termios locking IRQ-safe > alongside their interrupt-handler locking, preserving the caller's > interrupt state when releasing the port lock. > - Report RX DMA recovery after releasing the port lock, keeping the > state changes and interrupt-enable restoration serialized. > - Link to v5: > https://patch.msgid.link/20261024-submit-serial-8250-dma-cancel-v1-v5-0-9e5296892...@gmail.com > > Changes in v5: > - Add the posted serport write-wakeup deferral as a prerequisite for the > caller-locking preparation. > - Add a preparatory patch serializing asynchronous write-wakeup callers > with the port lock, including indirect CTS and transmit-helper calls. > Keep sleeping register accesses outside the lock and defer SCCNXP > notifications until its controller lock is released. > - Use the separately posted DesignWare BUSY-safe fractional-divisor fix > and Intel MID RX DMA timeout locking fix as prerequisites, leaving five > patches in this series. > - Separate serial-core write readiness from DMA storage reservations. Record > retirement during startup and shutdown while keeping writes and wakeups > gated until the port is ready. > - Wake deferred writers after successful startup or resume, including when > reopening with a retained FIFO, and restart any retained queued output. > - Keep the write-ready notification pending while retained output is at or > above the normal wakeup threshold, until TX completion drains it. > - Publish resume readiness under the TX restart lock without releasing a > reservation that may belong to a newly flushed transfer. > - Release 8250's TX reservation after shutdown has stopped DMA and unmapped > the source; serial core retains control of write readiness. > - Link to v4: > https://patch.msgid.link/20261023-submit-serial-8250-dma-cancel-v1-v4-0-e759de183...@gmail.com > > Changes in v4: > - Retain flushed TX reservations through shutdown and failed resume. Release > them after successful resume, or when allocating a new FIFO on reopen, > so retirement cannot wake writers into a closing port. > - Treat RX flush as complete once the channel is inactive, and clear the > shutdown guard before startup configures the UART and tests interrupts. > - Check completion after a failed pause so a transfer that finished before > its callback acquired the port lock is delivered and retired normally. > - Keep DesignWare's BUSY-safe divisor setter after fractional-divisor > discovery, writing DLF and DLL/DLH only after confirming DLAB. > - Link to v3: > https://patch.msgid.link/20261023-submit-serial-8250-dma-cancel-v1-v3-0-d78f9e4c4...@gmail.com > > Changes in v3: > - Defer write-ready wakeups while flushed TX storage is reserved, and > serialize the flush wakeup with the reservation under the port lock. > - Suppress ordinary TX starts during the reservation while preserving > high-priority flow-control characters, which use separate storage. > - Separate RX FIFO access from callback retirement, allowing PIO and the > DesignWare empty-FIFO timeout workaround after a successful pause and > termination while keeping the receive buffer reserved. > - Use the existing IER shadow for requested enables and a shared register > writer to keep receive interrupts masked throughout DMA error recovery, > including termios, RS485, modem-status and overrun-backoff updates. > - Preserve the timeout-enable bit across stop_rx(), exclude late shutdown > interrupts from PIO, and avoid FIFO resets during RX DMA recovery. > - Preserve the completion-path LSR read after stop_rx(), while gating DMA > resubmission on the receive interrupt enable. > - Pack the cancellation flags after moving all their accesses under the > port lock, including the recovery worker's snapshot and initialization. > - Apply the early-return, shared-helper and line-wrapping cleanups. > - Link to v2: > https://patch.msgid.link/20261022-submit-serial-8250-dma-cancel-v1-v2-0-088ea51e3...@gmail.com > > Changes in v2: > - Add serial-core helpers to reserve flushed transmit storage until DMA > retirement. Apply write backpressure during that interval and keep normal > TX using the FIFO directly, replacing the private transmit buffer in v1. > - Document the flush callback's reservation, writer backpressure and > retirement requirements, including release before shutdown returns. > - Split the OMAP completion refactor into a preparatory patch and move > the RZ/N1 preparation-order and shutdown PM fixes to independent > submissions, keeping four patches in this series. > - Take runtime PM references around worker UART accesses, and leave normal > RX retirement to release ownership without reading LSR or restarting DMA. > - Synchronize the queued TX ranges before preparing the descriptor and > return the mapping to CPU ownership before releasing the reservation. > - Keep the TX transfer length separate from FIFO cancellation, so a failed > termination can account completion without advancing the reset FIFO. > - Exclude late RX flush work during shutdown, including Intel MID DMA > timeout interrupts which are independent of UART_IER. > - Accept DMA_IN_PROGRESS after successful pause, and recover from failed > pause, termination or DMA_ERROR before handing the receiver to PIO. > - Preserve stop_rx() and shutdown across recovery, and retain the > DesignWare empty-FIFO timeout workaround when receiving through PIO. > - Apply the requested guard spacing and container_of() formatting. > - Link to v1: > https://patch.msgid.link/20261021-submit-serial-8250-dma-cancel-v1-v1-0-efe2b89f2...@gmail.com > > --- > James Hilliard (5): > serial: 8250_omap: separate locked TX DMA completion processing > serial: serialize asynchronous write wakeups with the port lock > serial: core: allow drivers to reserve flushed transmit storage > serial: 8250: drain canceled TX DMA before reusing its buffer > serial: 8250: retire canceled RX DMA before reusing the receive buffer > > drivers/tty/serial/21285.c | 2 + > drivers/tty/serial/8250/8250.h | 59 +++++++- > drivers/tty/serial/8250/8250_core.c | 2 +- > drivers/tty/serial/8250/8250_dma.c | 286 > +++++++++++++++++++++++++++--------- > drivers/tty/serial/8250/8250_dw.c | 27 +++- > drivers/tty/serial/8250/8250_omap.c | 38 +++-- > drivers/tty/serial/8250/8250_port.c | 31 ++-- > drivers/tty/serial/atmel_serial.c | 12 +- > drivers/tty/serial/clps711x.c | 23 ++- > drivers/tty/serial/cpm_uart.c | 2 + > drivers/tty/serial/fsl_lpuart.c | 2 +- > drivers/tty/serial/jsm/jsm_cls.c | 3 +- > drivers/tty/serial/jsm/jsm_neo.c | 9 +- > drivers/tty/serial/lantiq.c | 3 +- > drivers/tty/serial/ma35d1_serial.c | 6 +- > drivers/tty/serial/max3100.c | 6 +- > drivers/tty/serial/max310x.c | 9 +- > drivers/tty/serial/mux.c | 13 +- > drivers/tty/serial/mvebu-uart.c | 2 + > drivers/tty/serial/mxs-auart.c | 2 + > drivers/tty/serial/sb1250-duart.c | 14 +- > drivers/tty/serial/sccnxp.c | 45 ++++-- > drivers/tty/serial/serial_core.c | 100 +++++++++++-- > drivers/tty/serial/ucc_uart.c | 6 +- > include/linux/serial_core.h | 18 ++- > 25 files changed, 551 insertions(+), 169 deletions(-) > --- > base-commit: 1184f87e2790e8af9be3116f608d2e86b4792d7d > change-id: 20261021-submit-serial-8250-dma-cancel-v1-b208f84e89c1 > prerequisite-patch-id: 3604bfaa3a1c214997de1f11162b81a4541af5ab > prerequisite-patch-id: 79dd093ffb35e254e790dffb8887faf51b64f947 > prerequisite-patch-id: 80a5061d84c055a64c760268febed179c687b99f > prerequisite-patch-id: 7dbb404baf1f861982cf6a4b755d39cfec548223 > prerequisite-patch-id: 40881d81a27b3a1aa45203d171214faaf2197768 > prerequisite-patch-id: 4456eb7f800cb5d50a70c898e6d5a452a7f0bca4 > prerequisite-patch-id: c3d8ac0d54d1bfe43657964c517cfa4c7fde11af > prerequisite-patch-id: 48659e5ef3f5fb377d0b751f0830c0de4699262c > > Best regards, > -- > James Hilliard <[email protected]> > -- i.
