FAILED: patch "[PATCH] serial: sc16is7xx: remove useless enable of enhanced features" failed to apply to 6.1-stable tree

FAILED: patch "[PATCH] serial: sc16is7xx: remove useless enable of enhanced features" failed to apply to 6.1-stable tree

[gregkh]

The patch below does not apply to the 6.1-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 <stable@vger.kernel.org>.

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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 1c05bf6c0262f946571a37678250193e46b1ff0f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102739-fable-reroute-e6a6@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 1c05bf6c0262f946571a37678250193e46b1ff0f Mon Sep 17 00:00:00 2001
From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Date: Mon, 6 Oct 2025 10:20:02 -0400
Subject: [PATCH] serial: sc16is7xx: remove useless enable of enhanced features

Commit 43c51bb573aa ("sc16is7xx: make sure device is in suspend once
probed") permanently enabled access to the enhanced features in
sc16is7xx_probe(), and it is never disabled after that.

Therefore, remove re-enable of enhanced features in
sc16is7xx_set_baud(). This eliminates a potential useless read + write
cycle each time the baud rate is reconfigured.

Fixes: 43c51bb573aa ("sc16is7xx: make sure device is in suspend once probed")
Cc: stable <stable@kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://patch.msgid.link/20251006142002.177475-1-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 1a2c4c14f6aa..c7435595dce1 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -588,13 +588,6 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 		div /= prescaler;
 	}
 
-	/* Enable enhanced features */
-	sc16is7xx_efr_lock(port);
-	sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
-			      SC16IS7XX_EFR_ENABLE_BIT,
-			      SC16IS7XX_EFR_ENABLE_BIT);
-	sc16is7xx_efr_unlock(port);
-
 	/* If bit MCR_CLKSEL is set, the divide by 4 prescaler is activated. */
 	sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
 			      SC16IS7XX_MCR_CLKSEL_BIT,

[PATCH 6.1.y 1/4] serial: sc16is7xx: remove unused to_sc16is7xx_port macro

[Sasha Levin]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit 22a048b0749346b6e3291892d06b95278d5ba84a ]

This macro is not used anywhere.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230905181649.134720-1-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 1c05bf6c0262 ("serial: sc16is7xx: remove useless enable of enhanced features")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sc16is7xx.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 63573ef8b9142..a187ae217fc4c 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -358,7 +358,6 @@ static struct uart_driver sc16is7xx_uart = {
 static void sc16is7xx_ier_set(struct uart_port *port, u8 bit);
 static void sc16is7xx_stop_tx(struct uart_port *port);
 
-#define to_sc16is7xx_port(p,e)	((container_of((p), struct sc16is7xx_port, e)))
 #define to_sc16is7xx_one(p,e)	((container_of((p), struct sc16is7xx_one, e)))
 
 static u8 sc16is7xx_port_read(struct uart_port *port, u8 reg)
-- 
2.51.0

[PATCH 6.1.y 2/4] serial: sc16is7xx: reorder code to remove prototype declarations

[Sasha Levin]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit 2de8a1b46756b5a79d8447f99afdfe49e914225a ]

Move/reorder some functions to remove sc16is7xx_ier_set() and
sc16is7xx_stop_tx() prototypes declarations.

No functional change.

sc16is7xx_ier_set() was introduced in
commit cc4c1d05eb10 ("sc16is7xx: Properly resume TX after stop").

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20231221231823.2327894-16-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 1c05bf6c0262 ("serial: sc16is7xx: remove useless enable of enhanced features")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sc16is7xx.c | 75 ++++++++++++++++------------------
 1 file changed, 36 insertions(+), 39 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index a187ae217fc4c..f87fcde9a3d49 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -355,9 +355,6 @@ static struct uart_driver sc16is7xx_uart = {
 	.nr		= SC16IS7XX_MAX_DEVS,
 };
 
-static void sc16is7xx_ier_set(struct uart_port *port, u8 bit);
-static void sc16is7xx_stop_tx(struct uart_port *port);
-
 #define to_sc16is7xx_one(p,e)	((container_of((p), struct sc16is7xx_one, e)))
 
 static u8 sc16is7xx_port_read(struct uart_port *port, u8 reg)
@@ -415,6 +412,42 @@ static void sc16is7xx_power(struct uart_port *port, int on)
 			      on ? 0 : SC16IS7XX_IER_SLEEP_BIT);
 }
 
+static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)
+{
+	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
+	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+	lockdep_assert_held_once(&port->lock);
+
+	one->config.flags |= SC16IS7XX_RECONF_IER;
+	one->config.ier_mask |= bit;
+	one->config.ier_val &= ~bit;
+	kthread_queue_work(&s->kworker, &one->reg_work);
+}
+
+static void sc16is7xx_ier_set(struct uart_port *port, u8 bit)
+{
+	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
+	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+	lockdep_assert_held_once(&port->lock);
+
+	one->config.flags |= SC16IS7XX_RECONF_IER;
+	one->config.ier_mask |= bit;
+	one->config.ier_val |= bit;
+	kthread_queue_work(&s->kworker, &one->reg_work);
+}
+
+static void sc16is7xx_stop_tx(struct uart_port *port)
+{
+	sc16is7xx_ier_clear(port, SC16IS7XX_IER_THRI_BIT);
+}
+
+static void sc16is7xx_stop_rx(struct uart_port *port)
+{
+	sc16is7xx_ier_clear(port, SC16IS7XX_IER_RDI_BIT);
+}
+
 static const struct sc16is7xx_devtype sc16is74x_devtype = {
 	.name		= "SC16IS74X",
 	.nr_gpio	= 0,
@@ -891,42 +924,6 @@ static void sc16is7xx_reg_proc(struct kthread_work *ws)
 		sc16is7xx_reconf_rs485(&one->port);
 }
 
-static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)
-{
-	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
-	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
-
-	lockdep_assert_held_once(&port->lock);
-
-	one->config.flags |= SC16IS7XX_RECONF_IER;
-	one->config.ier_mask |= bit;
-	one->config.ier_val &= ~bit;
-	kthread_queue_work(&s->kworker, &one->reg_work);
-}
-
-static void sc16is7xx_ier_set(struct uart_port *port, u8 bit)
-{
-	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
-	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
-
-	lockdep_assert_held_once(&port->lock);
-
-	one->config.flags |= SC16IS7XX_RECONF_IER;
-	one->config.ier_mask |= bit;
-	one->config.ier_val |= bit;
-	kthread_queue_work(&s->kworker, &one->reg_work);
-}
-
-static void sc16is7xx_stop_tx(struct uart_port *port)
-{
-	sc16is7xx_ier_clear(port, SC16IS7XX_IER_THRI_BIT);
-}
-
-static void sc16is7xx_stop_rx(struct uart_port *port)
-{
-	sc16is7xx_ier_clear(port, SC16IS7XX_IER_RDI_BIT);
-}
-
 static void sc16is7xx_ms_proc(struct kthread_work *ws)
 {
 	struct sc16is7xx_one *one = to_sc16is7xx_one(ws, ms_work.work);
-- 
2.51.0

[PATCH 6.1.y 3/4] serial: sc16is7xx: refactor EFR lock

[Sasha Levin]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit 0c84bea0cabc4e2b98a3de88eeb4ff798931f056 ]

Move common code for EFR lock/unlock of mutex into functions for code reuse
and clarity.

With the addition of old_lcr, move irda_mode within struct sc16is7xx_one to
reduce memory usage:
    Before: /* size: 752, cachelines: 12, members: 10 */
    After:  /* size: 744, cachelines: 12, members: 10 */

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20231221231823.2327894-17-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 1c05bf6c0262 ("serial: sc16is7xx: remove useless enable of enhanced features")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sc16is7xx.c | 106 ++++++++++++++++++---------------
 1 file changed, 57 insertions(+), 49 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index f87fcde9a3d49..c0c2c1450e88d 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -329,8 +329,9 @@ struct sc16is7xx_one {
 	struct kthread_work		reg_work;
 	struct kthread_delayed_work	ms_work;
 	struct sc16is7xx_one_config	config;
-	bool				irda_mode;
 	unsigned int			old_mctrl;
+	u8				old_lcr; /* Value before EFR access. */
+	bool				irda_mode;
 };
 
 struct sc16is7xx_port {
@@ -412,6 +413,49 @@ static void sc16is7xx_power(struct uart_port *port, int on)
 			      on ? 0 : SC16IS7XX_IER_SLEEP_BIT);
 }
 
+/*
+ * In an amazing feat of design, the Enhanced Features Register (EFR)
+ * shares the address of the Interrupt Identification Register (IIR).
+ * Access to EFR is switched on by writing a magic value (0xbf) to the
+ * Line Control Register (LCR). Any interrupt firing during this time will
+ * see the EFR where it expects the IIR to be, leading to
+ * "Unexpected interrupt" messages.
+ *
+ * Prevent this possibility by claiming a mutex while accessing the EFR,
+ * and claiming the same mutex from within the interrupt handler. This is
+ * similar to disabling the interrupt, but that doesn't work because the
+ * bulk of the interrupt processing is run as a workqueue job in thread
+ * context.
+ */
+static void sc16is7xx_efr_lock(struct uart_port *port)
+{
+	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+	mutex_lock(&one->efr_lock);
+
+	/* Backup content of LCR. */
+	one->old_lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
+
+	/* Enable access to Enhanced register set */
+	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, SC16IS7XX_LCR_CONF_MODE_B);
+
+	/* Disable cache updates when writing to EFR registers */
+	regcache_cache_bypass(one->regmap, true);
+}
+
+static void sc16is7xx_efr_unlock(struct uart_port *port)
+{
+	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+	/* Re-enable cache updates when writing to normal registers */
+	regcache_cache_bypass(one->regmap, false);
+
+	/* Restore original content of LCR */
+	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, one->old_lcr);
+
+	mutex_unlock(&one->efr_lock);
+}
+
 static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)
 {
 	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
@@ -538,39 +582,12 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 		div /= prescaler;
 	}
 
-	/* In an amazing feat of design, the Enhanced Features Register shares
-	 * the address of the Interrupt Identification Register, and is
-	 * switched in by writing a magic value (0xbf) to the Line Control
-	 * Register. Any interrupt firing during this time will see the EFR
-	 * where it expects the IIR to be, leading to "Unexpected interrupt"
-	 * messages.
-	 *
-	 * Prevent this possibility by claiming a mutex while accessing the
-	 * EFR, and claiming the same mutex from within the interrupt handler.
-	 * This is similar to disabling the interrupt, but that doesn't work
-	 * because the bulk of the interrupt processing is run as a workqueue
-	 * job in thread context.
-	 */
-	mutex_lock(&one->efr_lock);
-
-	lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
-
-	/* Open the LCR divisors for configuration */
-	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
-			     SC16IS7XX_LCR_CONF_MODE_B);
-
 	/* Enable enhanced features */
-	regcache_cache_bypass(one->regmap, true);
+	sc16is7xx_efr_lock(port);
 	sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
 			      SC16IS7XX_EFR_ENABLE_BIT,
 			      SC16IS7XX_EFR_ENABLE_BIT);
-
-	regcache_cache_bypass(one->regmap, false);
-
-	/* Put LCR back to the normal mode */
-	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
-
-	mutex_unlock(&one->efr_lock);
+	sc16is7xx_efr_unlock(port);
 
 	/* If bit MCR_CLKSEL is set, the divide by 4 prescaler is activated. */
 	sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
@@ -580,7 +597,8 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 
 	mutex_lock(&one->efr_lock);
 
-	/* Open the LCR divisors for configuration */
+	/* Backup LCR and access special register set (DLL/DLH) */
+	lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
 			     SC16IS7XX_LCR_CONF_MODE_A);
 
@@ -590,7 +608,7 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 	sc16is7xx_port_write(port, SC16IS7XX_DLL_REG, div % 256);
 	regcache_cache_bypass(one->regmap, false);
 
-	/* Put LCR back to the normal mode */
+	/* Restore LCR and access to general register set */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
 
 	mutex_unlock(&one->efr_lock);
@@ -1073,17 +1091,7 @@ static void sc16is7xx_set_termios(struct uart_port *port,
 	if (!(termios->c_cflag & CREAD))
 		port->ignore_status_mask |= SC16IS7XX_LSR_BRK_ERROR_MASK;
 
-	/* As above, claim the mutex while accessing the EFR. */
-	mutex_lock(&one->efr_lock);
-
-	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
-			     SC16IS7XX_LCR_CONF_MODE_B);
-
 	/* Configure flow control */
-	regcache_cache_bypass(one->regmap, true);
-	sc16is7xx_port_write(port, SC16IS7XX_XON1_REG, termios->c_cc[VSTART]);
-	sc16is7xx_port_write(port, SC16IS7XX_XOFF1_REG, termios->c_cc[VSTOP]);
-
 	port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS);
 	if (termios->c_cflag & CRTSCTS) {
 		flow |= SC16IS7XX_EFR_AUTOCTS_BIT |
@@ -1095,16 +1103,16 @@ static void sc16is7xx_set_termios(struct uart_port *port,
 	if (termios->c_iflag & IXOFF)
 		flow |= SC16IS7XX_EFR_SWFLOW1_BIT;
 
-	sc16is7xx_port_update(port,
-			      SC16IS7XX_EFR_REG,
-			      SC16IS7XX_EFR_FLOWCTRL_BITS,
-			      flow);
-	regcache_cache_bypass(one->regmap, false);
-
 	/* Update LCR register */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
 
-	mutex_unlock(&one->efr_lock);
+	/* Update EFR registers */
+	sc16is7xx_efr_lock(port);
+	sc16is7xx_port_write(port, SC16IS7XX_XON1_REG, termios->c_cc[VSTART]);
+	sc16is7xx_port_write(port, SC16IS7XX_XOFF1_REG, termios->c_cc[VSTOP]);
+	sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
+			      SC16IS7XX_EFR_FLOWCTRL_BITS, flow);
+	sc16is7xx_efr_unlock(port);
 
 	/* Get baud rate generator configuration */
 	baud = uart_get_baud_rate(port, termios, old,
-- 
2.51.0

[PATCH 6.1.y 4/4] serial: sc16is7xx: remove useless enable of enhanced features

[Sasha Levin]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit 1c05bf6c0262f946571a37678250193e46b1ff0f ]

Commit 43c51bb573aa ("sc16is7xx: make sure device is in suspend once
probed") permanently enabled access to the enhanced features in
sc16is7xx_probe(), and it is never disabled after that.

Therefore, remove re-enable of enhanced features in
sc16is7xx_set_baud(). This eliminates a potential useless read + write
cycle each time the baud rate is reconfigured.

Fixes: 43c51bb573aa ("sc16is7xx: make sure device is in suspend once probed")
Cc: stable <stable@kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://patch.msgid.link/20251006142002.177475-1-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sc16is7xx.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index c0c2c1450e88d..458bf16543724 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -582,13 +582,6 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 		div /= prescaler;
 	}
 
-	/* Enable enhanced features */
-	sc16is7xx_efr_lock(port);
-	sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
-			      SC16IS7XX_EFR_ENABLE_BIT,
-			      SC16IS7XX_EFR_ENABLE_BIT);
-	sc16is7xx_efr_unlock(port);
-
 	/* If bit MCR_CLKSEL is set, the divide by 4 prescaler is activated. */
 	sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
 			      SC16IS7XX_MCR_CLKSEL_BIT,
-- 
2.51.0