linux-kernel - [PATCH v2 0/7] 8250 DW UART fixes when under constant Rx pressure

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Message-Id: <20260128105301.1869-1-ilpo.jarvinen@linux.intel.com>
Date: Wed, 28 Jan 2026 12:52:54 +0200
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	linux-serial@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	qianfan Zhao <qianfanguijin@....com>,
	Adriana Nicolae <adriana@...sta.com>
Cc: linux-kernel@...r.kernel.org,
	"Bandal, Shankar" <shankar.bandal@...el.com>,
	"Murthy, Shanth" <shanth.murthy@...el.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH v2 0/7] 8250 DW UART fixes when under constant Rx pressure

Hi all,

Here are fixes to 8250 DW UART conditions that mostly occur in scenarios
under constant Rx pressure which are made complicated by BUSY handling
of DW UARTs (used when !uart_16550_compatible).

A few of the changes touch also 8250_port but it's mostly moving existing
code around (except for the extra synchronize_irq() in shutdown).

I'll do UART_IIR_RX_TIMEOUT move to switch/case separately from this
fix series and a few other cleanups Andy brought up.


v2:
- Added Fixes tags pointing DW & INTC10EE introducing commits
- Added Cc stable to prerequisite patches
- Separate adding serial8250_handle_irq_locked() to own patch
- Put new exports to SERIAL_8250 namespace (eventually all 8250
  exports should move there, but out-of-scope for this series)
- Changes to no_int_count
	- Change type to u8
	- Use modulo in increment, add a define for it
	- Perform kick only on 4th NO_INT
- Use serial_port_in/out() throughout the series
- Add FIXME comments to ndelay(frame_time) about very low baud rates
- Add cleanup.h
- Tweak lockdep.h place among misordered includes
- Wording tweaks to changelogs and comments

Ilpo Järvinen (7):
  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: Add late synchronize_irq() to shutdown to handle DW UART
    BUSY
  serial: 8250_dw: Ensure BUSY is deasserted

 drivers/tty/serial/8250/8250.h      |  25 +++
 drivers/tty/serial/8250/8250_dw.c   | 309 ++++++++++++++++++++++------
 drivers/tty/serial/8250/8250_port.c |  69 ++++---
 include/linux/serial_8250.h         |   1 +
 4 files changed, 313 insertions(+), 91 deletions(-)


base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
-- 
2.39.5