[PATCH 2/2] serial: 8250_dw: remove clock-notifier infrastructure
From: Stepan Ionichev
Date: Thu May 14 2026 - 10:47:02 EST
The clock notifier and matching work_struct in dw8250_data were added
in 2020 for the Baikal-T1 SoC, whose multiple UART ports share a
single reference clock and need to be informed when another consumer
re-rates that clock.
Baikal SoC support has since been removed from the kernel (see e.g.
commit 5d6c477687ae ("clk: baikal-t1: Remove not-going-to-be-supported
code for Baikal SoC") and the matching removals across bus/, mtd/,
PCI/, hwmon/, memory/). No remaining in-tree user needs the
cross-device baudclk rate-change notification path: the only
configuration that wired up the notifier was Baikal-T1's shared
reference clock topology.
Drop the now-unused clock-notifier and its deferred-update worker:
- struct dw8250_data fields clk_notifier and clk_work,
- the clk_to_dw8250_data() and work_to_dw8250_data() helpers,
- the dw8250_clk_work_cb() and dw8250_clk_notifier_cb() callbacks,
- the INIT_WORK / notifier_call setup in dw8250_probe(),
- the clk_notifier_register() / queue_work() in dw8250_probe(),
- the matching clk_notifier_unregister() / flush_work() in
dw8250_remove(),
- the stale comment in dw8250_set_termios() about the worker
blocking,
- the linux/notifier.h and linux/workqueue.h includes that are
no longer used.
dw8250_set_termios() keeps calling clk_set_rate() directly, which is
all the remaining single-UART configurations require.
Signed-off-by: Stepan Ionichev <sozdayvek@xxxxxxxxx>
---
drivers/tty/serial/8250/8250_dw.c | 81 -------------------------------
1 file changed, 81 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 7dbd79a91..41c5abccd 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -19,13 +19,11 @@
#include <linux/lockdep.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
-#include <linux/notifier.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/property.h>
#include <linux/reset.h>
#include <linux/slab.h>
-#include <linux/workqueue.h>
#include <asm/byteorder.h>
@@ -86,8 +84,6 @@ struct dw8250_data {
u32 msr_mask_off;
struct clk *clk;
struct clk *pclk;
- struct notifier_block clk_notifier;
- struct work_struct clk_work;
struct reset_control *rst;
unsigned int skip_autocfg:1;
@@ -102,16 +98,6 @@ static inline struct dw8250_data *to_dw8250_data(struct dw8250_port_data *data)
return container_of(data, struct dw8250_data, data);
}
-static inline struct dw8250_data *clk_to_dw8250_data(struct notifier_block *nb)
-{
- return container_of(nb, struct dw8250_data, clk_notifier);
-}
-
-static inline struct dw8250_data *work_to_dw8250_data(struct work_struct *work)
-{
- return container_of(work, struct dw8250_data, clk_work);
-}
-
static inline u32 dw8250_modify_msr(struct uart_port *p, unsigned int offset, u32 value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
@@ -484,46 +470,6 @@ static int dw8250_handle_irq(struct uart_port *p)
return 1;
}
-static void dw8250_clk_work_cb(struct work_struct *work)
-{
- struct dw8250_data *d = work_to_dw8250_data(work);
- struct uart_8250_port *up;
- unsigned long rate;
-
- rate = clk_get_rate(d->clk);
- if (rate <= 0)
- return;
-
- up = serial8250_get_port(d->data.line);
-
- serial8250_update_uartclk(&up->port, rate);
-}
-
-static int dw8250_clk_notifier_cb(struct notifier_block *nb,
- unsigned long event, void *data)
-{
- struct dw8250_data *d = clk_to_dw8250_data(nb);
-
- /*
- * We have no choice but to defer the uartclk update due to two
- * deadlocks. First one is caused by a recursive mutex lock which
- * happens when clk_set_rate() is called from dw8250_set_termios().
- * Second deadlock is more tricky and is caused by an inverted order of
- * the clk and tty-port mutexes lock. It happens if clock rate change
- * is requested asynchronously while set_termios() is executed between
- * tty-port mutex lock and clk_set_rate() function invocation and
- * vise-versa. Anyway if we didn't have the reference clock alteration
- * in the dw8250_set_termios() method we wouldn't have needed this
- * deferred event handling complication.
- */
- if (event == POST_RATE_CHANGE) {
- queue_work(system_dfl_wq, &d->clk_work);
- return NOTIFY_OK;
- }
-
- return NOTIFY_DONE;
-}
-
static void
dw8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old)
{
@@ -547,10 +493,6 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
clk_disable_unprepare(d->clk);
rate = clk_round_rate(d->clk, newrate);
if (rate > 0) {
- /*
- * Note that any clock-notifier worker will block in
- * serial8250_update_uartclk() until we are done.
- */
ret = clk_set_rate(d->clk, newrate);
if (!ret)
p->uartclk = rate;
@@ -783,9 +725,6 @@ static int dw8250_probe(struct platform_device *pdev)
return dev_err_probe(dev, PTR_ERR(data->clk),
"failed to get baudclk\n");
- INIT_WORK(&data->clk_work, dw8250_clk_work_cb);
- data->clk_notifier.notifier_call = dw8250_clk_notifier_cb;
-
if (data->clk)
p->uartclk = clk_get_rate(data->clk);
@@ -843,20 +782,6 @@ static int dw8250_probe(struct platform_device *pdev)
if (data->data.line < 0)
return data->data.line;
- /*
- * Some platforms may provide a reference clock shared between several
- * devices. In this case any clock state change must be known to the
- * UART port at least post factum.
- */
- if (data->clk) {
- err = clk_notifier_register(data->clk, &data->clk_notifier);
- if (err) {
- serial8250_unregister_port(data->data.line);
- return dev_err_probe(dev, err, "Failed to set the clock notifier\n");
- }
- queue_work(system_dfl_wq, &data->clk_work);
- }
-
platform_set_drvdata(pdev, data);
pm_runtime_enable(dev);
@@ -871,12 +796,6 @@ static void dw8250_remove(struct platform_device *pdev)
pm_runtime_get_sync(dev);
- if (data->clk) {
- clk_notifier_unregister(data->clk, &data->clk_notifier);
-
- flush_work(&data->clk_work);
- }
-
serial8250_unregister_port(data->data.line);
pm_runtime_disable(dev);
--
2.43.0