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FAILED: patch "[PATCH] serial: sc16is7xx: enable THRI before filling TX FIFO" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 4 messages Aug 17 – Aug 21

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Stable branch TTY layer and serial drivers
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author maintainer
#0 lore raw

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 246ac114f485c2affb454240f3ea4fabfce22456
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026081754-ogle-alkalize-4f27@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 246ac114f485c2affb454240f3ea4fabfce22456 Mon Sep 17 00:00:00 2001
From: Luca Fresi <[email protected]>
Date: Wed, 22 Jul 2026 00:24:04 +0200
Subject: [PATCH] serial: sc16is7xx: enable THRI before filling TX FIFO

sc16is7xx_handle_tx() currently requests the THRI enable only after it has filled the TX FIFO. The request is asynchronous because the IER update is performed later by reg_work.

The SC16IS7xx generates a THRI interrupt when the TX FIFO crosses its trigger level. If the FIFO drains past that level before reg_work enables THRI, the chip does not generate a new interrupt. Characters remain queued indefinitely even though the hardware FIFO is empty.

This was observed on an SC16IS752 while both UART channels were active. During the stall the software TX buffer remained non-empty while TXLVL reported 64 bytes free, LSR reported THR and transmitter empty, IER had THRI enabled, and IIR reported no interrupt pending.

Enable THRI synchronously before filling the FIFO so the threshold crossing cannot be missed.

Fixes cc4c1d05eb10 ("sc16is7xx: Properly resume TX after stop")
Cc stable <[email protected]>
Signed-off-by Luca Fresi <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>
drivers/tty/serial/sc16is7xx.c +3 -0
index 6c97953d593b..9b152ead050f 100644
@@ -827,6 +827,9 @@ static void sc16is7xx_tx_proc(struct kthread_work *ws)
 		msleep(port->rs485.delay_rts_before_send);
 
 	guard(mutex)(&one->lock);
+	sc16is7xx_port_update(port, SC16IS7XX_IER_REG,
+			      SC16IS7XX_IER_THRI_BIT,
+			      SC16IS7XX_IER_THRI_BIT);
 	sc16is7xx_handle_tx(port);
 }
maintainer
#1 lore raw

PATCH 1/3 serial: sc16is7xx: rename EFR mutex with generic name

From: Hugo Villeneuve <[email protected]>

[ Upstream commit d9b2d7ddbb973b981c20b21e9228581bb156f66f ]

This mutex is used as a lock when accessing registers that share the same address space, not necessarily EFR registers.

For example, address 0x06 is shared by MSR, TCR and XOFF1 registers, independently of EFR.

Rename the mutex with a more generic name to avoid misinterpreting its usage.

Signed-off-by Hugo Villeneuve <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>

Stable-dep-of: 246ac114f485 ("serial: sc16is7xx: enable THRI before filling TX FIFO")

Signed-off-by Sasha Levin <[email protected]>
---
 drivers/tty/serial/sc16is7xx.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)
drivers/tty/serial/sc16is7xx.c +13 -13
index 01de811bc1501..f9d4aaff6239a 100644
@@ -327,7 +327,7 @@ struct sc16is7xx_one_config {
 struct sc16is7xx_one {
 	struct uart_port		port;
 	struct regmap			*regmap;
-	struct mutex			efr_lock; /* EFR registers access */
+	struct mutex			lock; /* For registers sharing same address space. */
 	struct kthread_work		tx_work;
 	struct kthread_work		reg_work;
 	struct kthread_delayed_work	ms_work;

@@ -433,7 +433,7 @@ static void sc16is7xx_efr_lock(struct uart_port *port)
 {
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
-	mutex_lock(&one->efr_lock);
+	mutex_lock(&one->lock);
 
 	/* Backup content of LCR. */
 	one->old_lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);

@@ -455,7 +455,7 @@ static void sc16is7xx_efr_unlock(struct uart_port *port)
 	/* Restore original content of LCR */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, one->old_lcr);
 
-	mutex_unlock(&one->efr_lock);
+	mutex_unlock(&one->lock);
 }
 
 static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)

@@ -590,7 +590,7 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 			      SC16IS7XX_MCR_CLKSEL_BIT,
 			      prescaler == 1 ? 0 : SC16IS7XX_MCR_CLKSEL_BIT);
 
-	mutex_lock(&one->efr_lock);
+	mutex_lock(&one->lock);
 
 	/* Backup LCR and access special register set (DLL/DLH) */
 	lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);

@@ -606,7 +606,7 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 	/* Restore LCR and access to general register set */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
 
-	mutex_unlock(&one->efr_lock);
+	mutex_unlock(&one->lock);
 
 	return DIV_ROUND_CLOSEST((clk / prescaler) / 16, div);
 }

@@ -753,7 +753,7 @@ static void sc16is7xx_update_mlines(struct sc16is7xx_one *one)
 	unsigned long flags;
 	unsigned int status, changed;
 
-	lockdep_assert_held_once(&one->efr_lock);
+	lockdep_assert_held_once(&one->lock);
 
 	status = sc16is7xx_get_hwmctrl(port);
 	changed = status ^ one->old_mctrl;

@@ -784,7 +784,7 @@ static bool sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
 	struct uart_port *port = &s->p[portno].port;
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
-	mutex_lock(&one->efr_lock);
+	mutex_lock(&one->lock);
 
 	iir = sc16is7xx_port_read(port, SC16IS7XX_IIR_REG);
 	if (iir & SC16IS7XX_IIR_NO_INT_BIT) {

@@ -831,7 +831,7 @@ static bool sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
 	}
 
 out_port_irq:
-	mutex_unlock(&one->efr_lock);
+	mutex_unlock(&one->lock);
 
 	return rc;
 }

@@ -863,9 +863,9 @@ static void sc16is7xx_tx_proc(struct kthread_work *ws)
 	    (port->rs485.delay_rts_before_send > 0))
 		msleep(port->rs485.delay_rts_before_send);
 
-	mutex_lock(&one->efr_lock);
+	mutex_lock(&one->lock);
 	sc16is7xx_handle_tx(port);
-	mutex_unlock(&one->efr_lock);
+	mutex_unlock(&one->lock);
 }
 
 static void sc16is7xx_reconf_rs485(struct uart_port *port)

@@ -932,9 +932,9 @@ static void sc16is7xx_ms_proc(struct kthread_work *ws)
 	struct sc16is7xx_port *s = dev_get_drvdata(one->port.dev);
 
 	if (one->port.state) {
-		mutex_lock(&one->efr_lock);
+		mutex_lock(&one->lock);
 		sc16is7xx_update_mlines(one);
-		mutex_unlock(&one->efr_lock);
+		mutex_unlock(&one->lock);
 
 		kthread_queue_delayed_work(&s->kworker, &one->ms_work, HZ);
 	}

@@ -1604,7 +1604,7 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
 		s->p[i].old_mctrl	= 0;
 		s->p[i].regmap		= regmaps[i];
 
-		mutex_init(&s->p[i].efr_lock);
+		mutex_init(&s->p[i].lock);
 
 		ret = uart_get_rs485_mode(&s->p[i].port);
 		if (ret)
Signature · 1 line
2.53.0
maintainer
#2 lore raw

PATCH 2/3 serial: sc16is7xx: use guards for simple mutex locks

From: Hugo Villeneuve <[email protected]>

[ Upstream commit 0f4f88bfd7e7bf3f3293045fffdc63586b0a889f ]

Guards can help to make the code more readable, so use them wherever they do so.

In sc16is7xx_port_irq(), labels and 'rc' locals are eliminated completely.

Signed-off-by Hugo Villeneuve <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>

Stable-dep-of: 246ac114f485 ("serial: sc16is7xx: enable THRI before filling TX FIFO")

Signed-off-by Sasha Levin <[email protected]>
---
 drivers/tty/serial/sc16is7xx.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)
drivers/tty/serial/sc16is7xx.c +8 -15
index f9d4aaff6239a..b534a830ab2a7 100644
@@ -11,6 +11,7 @@
 #define DEFAULT_SYMBOL_NAMESPACE "SERIAL_NXP_SC16IS7XX"
 
 #include <linux/bits.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/device.h>

@@ -779,18 +780,15 @@ static void sc16is7xx_update_mlines(struct sc16is7xx_one *one)
 
 static bool sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
 {
-	bool rc = true;
 	unsigned int iir, rxlen;
 	struct uart_port *port = &s->p[portno].port;
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
-	mutex_lock(&one->lock);
+	guard(mutex)(&one->lock);
 
 	iir = sc16is7xx_port_read(port, SC16IS7XX_IIR_REG);
-	if (iir & SC16IS7XX_IIR_NO_INT_BIT) {
-		rc = false;
-		goto out_port_irq;
-	}
+	if (iir & SC16IS7XX_IIR_NO_INT_BIT)
+		return false;
 
 	iir &= SC16IS7XX_IIR_ID_MASK;
 

@@ -830,10 +828,7 @@ static bool sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno)
 		break;
 	}
 
-out_port_irq:
-	mutex_unlock(&one->lock);
-
-	return rc;
+	return true;
 }
 
 static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)

@@ -863,9 +858,8 @@ static void sc16is7xx_tx_proc(struct kthread_work *ws)
 	    (port->rs485.delay_rts_before_send > 0))
 		msleep(port->rs485.delay_rts_before_send);
 
-	mutex_lock(&one->lock);
+	guard(mutex)(&one->lock);
 	sc16is7xx_handle_tx(port);
-	mutex_unlock(&one->lock);
 }
 
 static void sc16is7xx_reconf_rs485(struct uart_port *port)

@@ -932,9 +926,8 @@ static void sc16is7xx_ms_proc(struct kthread_work *ws)
 	struct sc16is7xx_port *s = dev_get_drvdata(one->port.dev);
 
 	if (one->port.state) {
-		mutex_lock(&one->lock);
-		sc16is7xx_update_mlines(one);
-		mutex_unlock(&one->lock);
+		scoped_guard(mutex, &one->lock)
+			sc16is7xx_update_mlines(one);
 
 		kthread_queue_delayed_work(&s->kworker, &one->ms_work, HZ);
 	}
Signature · 1 line
2.53.0
maintainer
#3 lore raw

PATCH 3/3 serial: sc16is7xx: enable THRI before filling TX FIFO

In reply to Sasha Levin

From: Luca Fresi <[email protected]>

[ Upstream commit 246ac114f485c2affb454240f3ea4fabfce22456 ]

sc16is7xx_handle_tx() currently requests the THRI enable only after it has filled the TX FIFO. The request is asynchronous because the IER update is performed later by reg_work.

The SC16IS7xx generates a THRI interrupt when the TX FIFO crosses its trigger level. If the FIFO drains past that level before reg_work enables THRI, the chip does not generate a new interrupt. Characters remain queued indefinitely even though the hardware FIFO is empty.

This was observed on an SC16IS752 while both UART channels were active. During the stall the software TX buffer remained non-empty while TXLVL reported 64 bytes free, LSR reported THR and transmitter empty, IER had THRI enabled, and IIR reported no interrupt pending.

Enable THRI synchronously before filling the FIFO so the threshold crossing cannot be missed.

Fixes cc4c1d05eb10 ("sc16is7xx: Properly resume TX after stop")
Cc stable <[email protected]>
Signed-off-by Luca Fresi <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>
Signed-off-by Sasha Levin <[email protected]>
---
 drivers/tty/serial/sc16is7xx.c | 3 +++
 1 file changed, 3 insertions(+)
drivers/tty/serial/sc16is7xx.c +3 -0
index b534a830ab2a7..80b821f7b9a22 100644
@@ -859,6 +859,9 @@ static void sc16is7xx_tx_proc(struct kthread_work *ws)
 		msleep(port->rs485.delay_rts_before_send);
 
 	guard(mutex)(&one->lock);
+	sc16is7xx_port_update(port, SC16IS7XX_IER_REG,
+			      SC16IS7XX_IER_THRI_BIT,
+			      SC16IS7XX_IER_THRI_BIT);
 	sc16is7xx_handle_tx(port);
 }
Signature · 1 line
2.53.0