* [PATCH 1/6] serial: 8250: Protect LCR write in shutdown
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, linux-kernel
Cc: Ilpo Järvinen, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
The 8250_dw driver needs to potentially perform very complex operations
during LCR writes because its BUSY handling prevents updates to LCR
while UART is BUSY (which is not fully under our control without those
complex operations). Thus, LCR writes should occur under port's lock.
Move LCR write under port's lock in serial8250_do_shutdown(). Also
split the LCR RMW so that the logic is on a separate line for clarity.
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_port.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 719faf92aa8a..f7a3c5555204 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2350,6 +2350,7 @@ static int serial8250_startup(struct uart_port *port)
void serial8250_do_shutdown(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
+ u32 lcr;
serial8250_rpm_get(up);
/*
@@ -2376,13 +2377,13 @@ void serial8250_do_shutdown(struct uart_port *port)
port->mctrl &= ~TIOCM_OUT2;
serial8250_set_mctrl(port, port->mctrl);
+
+ /* Disable break condition */
+ lcr = serial_port_in(port, UART_LCR);
+ lcr &= ~UART_LCR_SBC;
+ serial_port_out(port, UART_LCR, lcr);
}
- /*
- * Disable break condition and FIFOs
- */
- serial_port_out(port, UART_LCR,
- serial_port_in(port, UART_LCR) & ~UART_LCR_SBC);
serial8250_clear_fifos(up);
rsa_disable(up);
--
2.39.5
^ permalink raw reply related
* [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, Ilpo Järvinen, linux-kernel
Cc: Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
When DW UART is configured with BUSY flag, LCR writes may not always
succeed which can make any LCR write complex and very expensive.
Performing write directly can trigger IRQ and the driver has to perform
complex and distruptive sequence while retrying the write.
Therefore, it's better to avoid doing LCR write that would not change
the value of the LCR register. Add LCR write avoidance code into the
8250_dw driver's serial_out functions.
Reported-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_dw.c | 32 +++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 27af83f0ff46..57a760b43da9 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -181,6 +181,23 @@ static void dw8250_check_lcr(struct uart_port *p, unsigned int offset, u32 value
*/
}
+/*
+ * With BUSY, LCR writes can be very expensive (IRQ + complex retry logic).
+ * If the write would not change the value of the LCR register, skip write
+ * entirely.
+ */
+static bool dw8250_can_skip_reg_write(struct uart_port *p, unsigned int offset, u32 value)
+{
+ struct dw8250_data *d = to_dw8250_data(p->private_data);
+ u32 lcr;
+
+ if (offset != UART_LCR || d->uart_16550_compatible)
+ return false;
+
+ lcr = serial_port_in(p, offset);
+ return lcr == value;
+}
+
/* Returns once the transmitter is empty or we run out of retries */
static void dw8250_tx_wait_empty(struct uart_port *p)
{
@@ -207,12 +224,18 @@ static void dw8250_tx_wait_empty(struct uart_port *p)
static void dw8250_serial_out(struct uart_port *p, unsigned int offset, u32 value)
{
+ if (dw8250_can_skip_reg_write(p, offset, value))
+ return;
+
writeb(value, p->membase + (offset << p->regshift));
dw8250_check_lcr(p, offset, value);
}
static void dw8250_serial_out38x(struct uart_port *p, unsigned int offset, u32 value)
{
+ if (dw8250_can_skip_reg_write(p, offset, value))
+ return;
+
/* Allow the TX to drain before we reconfigure */
if (offset == UART_LCR)
dw8250_tx_wait_empty(p);
@@ -237,6 +260,9 @@ static u32 dw8250_serial_inq(struct uart_port *p, unsigned int offset)
static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 value)
{
+ if (dw8250_can_skip_reg_write(p, offset, value))
+ return;
+
value &= 0xff;
__raw_writeq(value, p->membase + (offset << p->regshift));
/* Read back to ensure register write ordering. */
@@ -248,6 +274,9 @@ static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 val
static void dw8250_serial_out32(struct uart_port *p, unsigned int offset, u32 value)
{
+ if (dw8250_can_skip_reg_write(p, offset, value))
+ return;
+
writel(value, p->membase + (offset << p->regshift));
dw8250_check_lcr(p, offset, value);
}
@@ -261,6 +290,9 @@ static u32 dw8250_serial_in32(struct uart_port *p, unsigned int offset)
static void dw8250_serial_out32be(struct uart_port *p, unsigned int offset, u32 value)
{
+ if (dw8250_can_skip_reg_write(p, offset, value))
+ return;
+
iowrite32be(value, p->membase + (offset << p->regshift));
dw8250_check_lcr(p, offset, value);
}
--
2.39.5
^ permalink raw reply related
* [PATCH 3/6] serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, Ilpo Järvinen, linux-kernel
Cc: Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
dw8250_handle_irq() takes port's lock multiple times with no good
reason to release it in between and calls serial8250_handle_irq()
that also takes port's lock.
As serial8250_handle_irq() takes port's lock itself, create
serial8250_handle_irq_locked() that allows caller to hold port's lock
across the call. Take port's lock only once in dw8250_handle_irq() and
call serial8250_handle_irq_locked() directly.
As IIR_NO_INT check in serial8250_handle_irq() was outside of port's
lock, it has to be done already in dw8250_handle_irq().
DW UART can, in addition to IIR_NO_INT, report BUSY_DETECT (0x7) which
collided with the IIR_NO_INT (0x1) check in serial8250_handle_irq()
(because & is used instead of ==) meaning that no other work is done by
serial8250_handle_irq() during an BUSY_DETECT interrupt.
This allows reorganizing code in dw8250_handle_irq() to do both
IIR_NO_INT and BUSY_DETECT handling right at the start simplifying
the logic.
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_dw.c | 35 ++++++++++++++++-------------
drivers/tty/serial/8250/8250_port.c | 24 +++++++++++++-------
include/linux/serial_8250.h | 1 +
3 files changed, 36 insertions(+), 24 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 57a760b43da9..7cee89f14179 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -9,6 +9,8 @@
* LCR is written whilst busy. If it is, then a busy detect interrupt is
* raised, the LCR needs to be rewritten and the uart status register read.
*/
+#include <linux/bitfield.h>
+#include <linux/bits.h>
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/device.h>
@@ -40,6 +42,8 @@
#define RZN1_UART_RDMACR 0x110 /* DMA Control Register Receive Mode */
/* DesignWare specific register fields */
+#define DW_UART_IIR_IID GENMASK(3, 0)
+
#define DW_UART_MCR_SIRE BIT(6)
/* Renesas specific register fields */
@@ -313,7 +317,19 @@ static int dw8250_handle_irq(struct uart_port *p)
bool rx_timeout = (iir & 0x3f) == UART_IIR_RX_TIMEOUT;
unsigned int quirks = d->pdata->quirks;
unsigned int status;
- unsigned long flags;
+
+ switch (FIELD_GET(DW_UART_IIR_IID, iir)) {
+ case UART_IIR_NO_INT:
+ return 0;
+
+ case UART_IIR_BUSY:
+ /* Clear the USR */
+ serial_port_in(p, d->pdata->usr_reg);
+
+ return 1;
+ }
+
+ guard(uart_port_lock_irqsave)(p);
/*
* There are ways to get Designware-based UARTs into a state where
@@ -326,20 +342,15 @@ static int dw8250_handle_irq(struct uart_port *p)
* so we limit the workaround only to non-DMA mode.
*/
if (!up->dma && rx_timeout) {
- uart_port_lock_irqsave(p, &flags);
status = serial_lsr_in(up);
if (!(status & (UART_LSR_DR | UART_LSR_BI)))
serial_port_in(p, UART_RX);
-
- uart_port_unlock_irqrestore(p, flags);
}
/* Manually stop the Rx DMA transfer when acting as flow controller */
if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
- uart_port_lock_irqsave(p, &flags);
status = serial_lsr_in(up);
- uart_port_unlock_irqrestore(p, flags);
if (status & (UART_LSR_DR | UART_LSR_BI)) {
dw8250_writel_ext(p, RZN1_UART_RDMACR, 0);
@@ -347,17 +358,9 @@ static int dw8250_handle_irq(struct uart_port *p)
}
}
- if (serial8250_handle_irq(p, iir))
- return 1;
-
- if ((iir & UART_IIR_BUSY) == UART_IIR_BUSY) {
- /* Clear the USR */
- serial_port_in(p, d->pdata->usr_reg);
+ serial8250_handle_irq_locked(p, iir);
- return 1;
- }
-
- return 0;
+ return 1;
}
static void dw8250_clk_work_cb(struct work_struct *work)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index f7a3c5555204..02576ed30abb 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -16,6 +16,7 @@
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/irq.h>
+#include <linux/lockdep.h>
#include <linux/console.h>
#include <linux/gpio/consumer.h>
#include <linux/sysrq.h>
@@ -1782,20 +1783,16 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
}
/*
- * This handles the interrupt from one port.
+ * Context: port's lock must be held by the caller.
*/
-int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
+void serial8250_handle_irq_locked(struct uart_port *port, unsigned int iir)
{
struct uart_8250_port *up = up_to_u8250p(port);
struct tty_port *tport = &port->state->port;
bool skip_rx = false;
- unsigned long flags;
u16 status;
- if (iir & UART_IIR_NO_INT)
- return 0;
-
- uart_port_lock_irqsave(port, &flags);
+ lockdep_assert_held_once(&port->lock);
status = serial_lsr_in(up);
@@ -1828,8 +1825,19 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
else if (!up->dma->tx_running)
__stop_tx(up);
}
+}
+EXPORT_SYMBOL_GPL(serial8250_handle_irq_locked);
- uart_unlock_and_check_sysrq_irqrestore(port, flags);
+/*
+ * This handles the interrupt from one port.
+ */
+int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
+{
+ if (iir & UART_IIR_NO_INT)
+ return 0;
+
+ guard(uart_port_lock_irqsave)(port);
+ serial8250_handle_irq_locked(port, iir);
return 1;
}
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 01efdce0fda0..a95b2d143d24 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -195,6 +195,7 @@ void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl);
void serial8250_do_set_divisor(struct uart_port *port, unsigned int baud,
unsigned int quot);
int fsl8250_handle_irq(struct uart_port *port);
+void serial8250_handle_irq_locked(struct uart_port *port, unsigned int iir);
int serial8250_handle_irq(struct uart_port *port, unsigned int iir);
u16 serial8250_rx_chars(struct uart_8250_port *up, u16 lsr);
void serial8250_read_char(struct uart_8250_port *up, u16 lsr);
--
2.39.5
^ permalink raw reply related
* [PATCH 4/6] serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, Ilpo Järvinen, linux-kernel
Cc: Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
INTC10EE UART can end up into an interrupt storm where it reports
IIR_NO_INT (0x1). If the storm happens during active UART operation, it
is promptly stopped by IIR value change due to Rx or Tx events.
However, when there is no activity, either due to idle serial line or
due to specific circumstances such as during shutdown that writes
IER=0, there is nothing to stop the storm.
During shutdown the storm is particularly problematic because
serial8250_do_shutdown() calls synchronize_irq() that will hang in
waiting for the storm to finish which never happens.
This problem can also result in triggering a warning:
irq 45: nobody cared (try booting with the "irqpoll" option)
[...snip...]
handlers:
serial8250_interrupt
Disabling IRQ #45
Normal means to reset interrupt status by reading LSR, MSR, USR, or RX
register do not result in the UART deasserting the IRQ.
Add a quirk to INTC10EE UARTs to enable Tx interrupts if UART's Tx is
currently empty and inactive. Rework IIR_NO_INT to keep track of the
number of consecutive IIR_NO_INT, and on third one perform the quirk.
Enabling Tx interrupts should change IIR value from IIR_NO_INT to
IIR_THRI which has been observed to stop the storm.
Reported-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_dw.c | 60 ++++++++++++++++++++++++++++---
1 file changed, 56 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 7cee89f14179..a40c0851f39c 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -60,6 +60,7 @@
#define DW_UART_QUIRK_IS_DMA_FC BIT(3)
#define DW_UART_QUIRK_APMC0D08 BIT(4)
#define DW_UART_QUIRK_CPR_VALUE BIT(5)
+#define DW_UART_QUIRK_IER_KICK BIT(6)
struct dw8250_platform_data {
u8 usr_reg;
@@ -81,6 +82,8 @@ struct dw8250_data {
unsigned int skip_autocfg:1;
unsigned int uart_16550_compatible:1;
+
+ u64 no_int_count;
};
static inline struct dw8250_data *to_dw8250_data(struct dw8250_port_data *data)
@@ -308,6 +311,29 @@ static u32 dw8250_serial_in32be(struct uart_port *p, unsigned int offset)
return dw8250_modify_msr(p, offset, value);
}
+/*
+ * INTC10EE UART can IRQ storm while reporting IIR_NO_INT. Inducing IIR value
+ * change has been observed to break the storm.
+ *
+ * If Tx is empty (THRE asserted), we use here IER_THRI to cause IIR_NO_INT ->
+ * IIR_THRI transition.
+ */
+static void dw8250_quirk_ier_kick(struct uart_port *p)
+{
+ struct uart_8250_port *up = up_to_u8250p(p);
+ u32 lsr;
+
+ if (up->ier & UART_IER_THRI)
+ return;
+
+ lsr = serial_lsr_in(up);
+ if (!(lsr & UART_LSR_THRE))
+ return;
+
+ serial_out(up, UART_IER, up->ier | UART_IER_THRI);
+ serial_in(up, UART_LCR); /* safe, no side-effects */
+ serial_out(up, UART_IER, up->ier);
+}
static int dw8250_handle_irq(struct uart_port *p)
{
@@ -318,18 +344,29 @@ static int dw8250_handle_irq(struct uart_port *p)
unsigned int quirks = d->pdata->quirks;
unsigned int status;
+ guard(uart_port_lock_irqsave)(p);
+
switch (FIELD_GET(DW_UART_IIR_IID, iir)) {
case UART_IIR_NO_INT:
+ if (d->uart_16550_compatible || up->dma)
+ return 0;
+
+ d->no_int_count++;
+ if (d->no_int_count > 2 && quirks & DW_UART_QUIRK_IER_KICK)
+ dw8250_quirk_ier_kick(p);
+
return 0;
case UART_IIR_BUSY:
/* Clear the USR */
serial_port_in(p, d->pdata->usr_reg);
+ d->no_int_count = 0;
+
return 1;
}
- guard(uart_port_lock_irqsave)(p);
+ d->no_int_count = 0;
/*
* There are ways to get Designware-based UARTs into a state where
@@ -562,6 +599,14 @@ static void dw8250_reset_control_assert(void *data)
reset_control_assert(data);
}
+static void dw8250_shutdown(struct uart_port *port)
+{
+ struct dw8250_data *d = to_dw8250_data(port->private_data);
+
+ serial8250_do_shutdown(port);
+ d->no_int_count = 0;
+}
+
static int dw8250_probe(struct platform_device *pdev)
{
struct uart_8250_port uart = {}, *up = &uart;
@@ -685,10 +730,12 @@ static int dw8250_probe(struct platform_device *pdev)
dw8250_quirks(p, data);
/* If the Busy Functionality is not implemented, don't handle it */
- if (data->uart_16550_compatible)
+ if (data->uart_16550_compatible) {
p->handle_irq = NULL;
- else if (data->pdata)
+ } else if (data->pdata) {
p->handle_irq = dw8250_handle_irq;
+ p->shutdown = dw8250_shutdown;
+ }
dw8250_setup_dma_filter(p, data);
@@ -815,6 +862,11 @@ static const struct dw8250_platform_data dw8250_skip_set_rate_data = {
.quirks = DW_UART_QUIRK_SKIP_SET_RATE,
};
+static const struct dw8250_platform_data dw8250_intc10ee = {
+ .usr_reg = DW_UART_USR,
+ .quirks = DW_UART_QUIRK_IER_KICK,
+};
+
static const struct of_device_id dw8250_of_match[] = {
{ .compatible = "snps,dw-apb-uart", .data = &dw8250_dw_apb },
{ .compatible = "cavium,octeon-3860-uart", .data = &dw8250_octeon_3860_data },
@@ -844,7 +896,7 @@ static const struct acpi_device_id dw8250_acpi_match[] = {
{ "INT33C5", (kernel_ulong_t)&dw8250_dw_apb },
{ "INT3434", (kernel_ulong_t)&dw8250_dw_apb },
{ "INT3435", (kernel_ulong_t)&dw8250_dw_apb },
- { "INTC10EE", (kernel_ulong_t)&dw8250_dw_apb },
+ { "INTC10EE", (kernel_ulong_t)&dw8250_intc10ee },
{ },
};
MODULE_DEVICE_TABLE(acpi, dw8250_acpi_match);
--
2.39.5
^ permalink raw reply related
* [PATCH 5/6] serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, linux-kernel
Cc: Ilpo Järvinen, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
When DW UART is !uart_16550_compatible, it can indicate BUSY at any
point (when under constant Rx pressure) unless a complex sequence of
steps is performed. Any LCR write can run a foul with the condition
that prevents writing LCR while the UART is BUSY, which triggers
BUSY_DETECT interrupt that seems unmaskable using IER bits.
Normal flow is that dw8250_handle_irq() handles BUSY_DETECT condition
by reading USR register. This BUSY feature, however, breaks the
assumptions made in serial8250_do_shutdown(), which runs
synchronize_irq() after clearing IER and assumes no interrupts can
occur after that point but then proceeds to update LCR, which on DW
UART can trigger an interrupt.
If serial8250_do_shutdown() releases the interrupt handler before the
handler has run and processed the BUSY_DETECT condition by read the USR
register, the IRQ is not deasserted resulting in interrupt storm that
triggers "irq x: nobody cared" warning leading to disabling the IRQ.
Add late synchronize_irq() into serial8250_do_shutdown() to ensure
BUSY_DETECT from DW UART is handled before port's interrupt handler is
released. Alternative would be to add DW UART specific shutdown
function but it would mostly duplicate the generic code and the extra
synchronize_irq() seems pretty harmless in serial8250_do_shutdown().
Reported-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_port.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 02576ed30abb..fa982e5cbe90 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2401,6 +2401,12 @@ void serial8250_do_shutdown(struct uart_port *port)
* the IRQ chain.
*/
serial_port_in(port, UART_RX);
+ /*
+ * LCR writes on DW UART can trigger late (unmaskable) IRQs.
+ * Handle them before releasing the handler.
+ */
+ synchronize_irq(port->irq);
+
serial8250_rpm_put(up);
up->ops->release_irq(up);
--
2.39.5
^ permalink raw reply related
* [PATCH 6/6] serial: 8250_dw: Ensure BUSY is deasserted
From: Ilpo Järvinen @ 2026-01-23 17:27 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, linux-serial, Andy Shevchenko,
qianfan Zhao, Adriana Nicolae, Ilpo Järvinen, Markus Mayer,
Tim Kryger, Matt Porter, Heikki Krogerus, Jamie Iles,
linux-kernel
Cc: stable, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-1-ilpo.jarvinen@linux.intel.com>
DW UART cannot write to LCR, DLL, and DLH while BUSY is asserted.
Existance of BUSY depends on uart_16550_compatible, if UART HW is
configured with 16550 compatible those registers can always be written.
There currently is dw8250_force_idle() which attempts to archive
non-BUSY state by disabling FIFO, however, the solution is unreliable
when Rx keeps getting more and more characters.
Create a sequence of operations to enforce that ensures UART cannot
keep BUSY asserted indefinitely. The new sequence relies on enabling
loopback mode temporarily to prevent incoming Rx characters keeping
UART BUSY.
Ensure no Tx in ongoing while the UART is switches into the loopback
mode (requires exporting serial8250_fifo_wait_for_lsr_thre() and adding
DMA Tx pause/resume functions).
According to tests performed by Adriana Nicolae <adriana@arista.com>,
simply disabling FIFO or clearing FIFOs only once does not always
ensure BUSY is deasserted but up to two tries may be needed. This could
be related to ongoing Rx of a character (a guess, not known for sure).
Therefore, retry FIFO clearing a few times (retry limit 4 is arbitrary
number but using, e.g., p->fifosize seems overly large). Tests
performed by others did not exhibit similar challenge but it does not
seem harmful to leave the FIFO clearing loop in place for all DW UARTs
with BUSY functionality.
Use the new dw8250_idle_enter/exit() to do divisor writes and LCR
writes. In case of plain LCR writes, opportunistically try to update
LCR first and only invoke dw8250_idle_enter() if the write did not
succeed (it has been observed that in practice most LCR writes do
succeed without complications).
This issue was first reported by qianfan Zhao who put lots of debugging
effort into understanding the solution space.
Fixes: c49436b657d0 ("serial: 8250_dw: Improve unwritable LCR workaround")
Fixes: 7d4008ebb1c9 ("tty: add a DesignWare 8250 driver")
Cc: <stable@vger.kernel.org>
Reported-by: qianfan Zhao <qianfanguijin@163.com>
Link: https://lore.kernel.org/linux-serial/289bb78a-7509-1c5c-2923-a04ed3b6487d@163.com/
Reported-by: Adriana Nicolae <adriana@arista.com>
Link: https://lore.kernel.org/linux-serial/20250819182322.3451959-1-adriana@arista.com/
Reported-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250.h | 25 ++++
drivers/tty/serial/8250/8250_dw.c | 172 ++++++++++++++++++++--------
drivers/tty/serial/8250/8250_port.c | 28 ++---
3 files changed, 166 insertions(+), 59 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 8caecfc85d93..77fe0588fd6b 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -175,7 +175,9 @@ static unsigned int __maybe_unused serial_icr_read(struct uart_8250_port *up,
return value;
}
+void serial8250_clear_fifos(struct uart_8250_port *p);
void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p);
+void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count);
void serial8250_rpm_get(struct uart_8250_port *p);
void serial8250_rpm_put(struct uart_8250_port *p);
@@ -400,6 +402,26 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)
return dma && dma->tx_running;
}
+
+static inline void serial8250_tx_dma_pause(struct uart_8250_port *p)
+{
+ struct uart_8250_dma *dma = p->dma;
+
+ if (!dma->tx_running)
+ return;
+
+ dmaengine_pause(dma->txchan);
+}
+
+static inline void serial8250_tx_dma_resume(struct uart_8250_port *p)
+{
+ struct uart_8250_dma *dma = p->dma;
+
+ if (!dma->tx_running)
+ return;
+
+ dmaengine_resume(dma->txchan);
+}
#else
static inline int serial8250_tx_dma(struct uart_8250_port *p)
{
@@ -421,6 +443,9 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)
{
return false;
}
+
+static inline void serial8250_tx_dma_pause(struct uart_8250_port *p) { }
+static inline void serial8250_tx_dma_resume(struct uart_8250_port *p) { }
#endif
static inline int ns16550a_goto_highspeed(struct uart_8250_port *up)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index a40c0851f39c..8166ed15fd08 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -15,6 +15,7 @@
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/io.h>
+#include <linux/lockdep.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/notifier.h>
@@ -46,6 +47,8 @@
#define DW_UART_MCR_SIRE BIT(6)
+#define DW_UART_USR_BUSY BIT(0)
+
/* Renesas specific register fields */
#define RZN1_UART_xDMACR_DMA_EN BIT(0)
#define RZN1_UART_xDMACR_1_WORD_BURST (0 << 1)
@@ -82,6 +85,7 @@ struct dw8250_data {
unsigned int skip_autocfg:1;
unsigned int uart_16550_compatible:1;
+ unsigned int in_idle:1;
u64 no_int_count;
};
@@ -115,77 +119,152 @@ static inline u32 dw8250_modify_msr(struct uart_port *p, unsigned int offset, u3
}
/*
- * This function is being called as part of the uart_port::serial_out()
- * routine. Hence, it must not call serial_port_out() or serial_out()
- * against the modified registers here, i.e. LCR.
+ * Ensure BUSY is not asserted. If DW UART is configured with
+ * !uart_16550_compatible, the writes to LCR, DLL, and DLH fail while
+ * BUSY is asserted.
+ *
+ * Context: port's lock must be held
*/
-static void dw8250_force_idle(struct uart_port *p)
+static int dw8250_idle_enter(struct uart_port *p)
{
+ struct dw8250_data *d = to_dw8250_data(p->private_data);
struct uart_8250_port *up = up_to_u8250p(p);
- unsigned int lsr;
+ unsigned int usr_reg = DW_UART_USR;
+ int retries;
+ u32 lsr;
- /*
- * The following call currently performs serial_out()
- * against the FCR register. Because it differs to LCR
- * there will be no infinite loop, but if it ever gets
- * modified, we might need a new custom version of it
- * that avoids infinite recursion.
- */
- serial8250_clear_and_reinit_fifos(up);
+ lockdep_assert_held_once(&p->lock);
+
+ if (d->uart_16550_compatible)
+ return 0;
+
+ if (d->pdata)
+ usr_reg = d->pdata->usr_reg;
+
+ d->in_idle = 1;
+
+ /* Prevent triggering interrupt from RBR filling */
+ p->serial_out(p, UART_IER, 0);
+
+ if (up->dma) {
+ serial8250_rx_dma_flush(up);
+ if (serial8250_tx_dma_running(up))
+ serial8250_tx_dma_pause(up);
+ }
/*
- * With PSLVERR_RESP_EN parameter set to 1, the device generates an
- * error response when an attempt to read an empty RBR with FIFO
- * enabled.
+ * Wait until Tx becomes empty + one extra frame time to ensure all bits
+ * have been sent on the wire.
*/
- if (up->fcr & UART_FCR_ENABLE_FIFO) {
- lsr = serial_port_in(p, UART_LSR);
- if (!(lsr & UART_LSR_DR))
- return;
+ serial8250_fifo_wait_for_lsr_thre(up, p->fifosize);
+ ndelay(p->frame_time);
+
+ p->serial_out(p, UART_MCR, up->mcr | UART_MCR_LOOP);
+
+ retries = 4; /* Arbitrary limit, 2 was always enough in tests */
+ do {
+ serial8250_clear_fifos(up);
+ if (!(p->serial_in(p, usr_reg) & DW_UART_USR_BUSY))
+ break;
+ ndelay(p->frame_time);
+ } while (--retries);
+
+ lsr = serial_lsr_in(up);
+ if (lsr & UART_LSR_DR) {
+ p->serial_in(p, UART_RX);
+ up->lsr_saved_flags = 0;
}
- serial_port_in(p, UART_RX);
+ /* Now guaranteed to have BUSY deasserted? Just sanity check */
+ if (p->serial_in(p, usr_reg) & DW_UART_USR_BUSY)
+ return -EBUSY;
+
+ return 0;
+}
+
+static void dw8250_idle_exit(struct uart_port *p)
+{
+ struct dw8250_data *d = to_dw8250_data(p->private_data);
+ struct uart_8250_port *up = up_to_u8250p(p);
+
+ if (d->uart_16550_compatible)
+ return;
+
+ if (up->capabilities & UART_CAP_FIFO)
+ p->serial_out(p, UART_FCR, up->fcr);
+ p->serial_out(p, UART_MCR, up->mcr);
+ p->serial_out(p, UART_IER, up->ier);
+
+ /* DMA Rx is restarted by IRQ handler as needed. */
+ if (up->dma)
+ serial8250_tx_dma_resume(up);
+
+ d->in_idle = 0;
+}
+
+static void dw8250_set_divisor(struct uart_port *p, unsigned int baud,
+ unsigned int quot, unsigned int quot_frac)
+{
+ struct uart_8250_port *up = up_to_u8250p(p);
+ int ret;
+
+ ret = dw8250_idle_enter(p);
+ if (ret < 0)
+ goto idle_failed;
+
+ p->serial_out(p, UART_LCR, up->lcr | UART_LCR_DLAB);
+ if (!(p->serial_in(p, UART_LCR) & UART_LCR_DLAB))
+ goto idle_failed;
+
+ serial_dl_write(up, quot);
+ p->serial_out(p, UART_LCR, up->lcr);
+
+idle_failed:
+ dw8250_idle_exit(p);
}
/*
* This function is being called as part of the uart_port::serial_out()
- * routine. Hence, it must not call serial_port_out() or serial_out()
- * against the modified registers here, i.e. LCR.
+ * routine. Hence, special care must be taken when serial_port_out() or
+ * serial_out() against the modified registers here, i.e. LCR (d->in_idle is
+ * used to break recursion loop).
*/
static void dw8250_check_lcr(struct uart_port *p, unsigned int offset, u32 value)
{
struct dw8250_data *d = to_dw8250_data(p->private_data);
- void __iomem *addr = p->membase + (offset << p->regshift);
- int tries = 1000;
+ u32 lcr;
+ int ret;
if (offset != UART_LCR || d->uart_16550_compatible)
return;
- /* Make sure LCR write wasn't ignored */
- while (tries--) {
- u32 lcr = serial_port_in(p, offset);
+ lcr = p->serial_in(p, UART_LCR);
- if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
- return;
+ /* Make sure LCR write wasn't ignored */
+ if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
+ return;
- dw8250_force_idle(p);
+ if (d->in_idle) {
+ /*
+ * FIXME: this deadlocks if port->lock is already held
+ * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+ */
+ return;
+ }
-#ifdef CONFIG_64BIT
- if (p->type == PORT_OCTEON)
- __raw_writeq(value & 0xff, addr);
- else
-#endif
- if (p->iotype == UPIO_MEM32)
- writel(value, addr);
- else if (p->iotype == UPIO_MEM32BE)
- iowrite32be(value, addr);
- else
- writeb(value, addr);
+ ret = dw8250_idle_enter(p);
+ if (ret < 0) {
+ /*
+ * FIXME: this deadlocks if port->lock is already held
+ * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+ */
+ goto idle_failed;
}
- /*
- * FIXME: this deadlocks if port->lock is already held
- * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
- */
+
+ p->serial_out(p, UART_LCR, value);
+
+idle_failed:
+ dw8250_idle_exit(p);
}
/*
@@ -627,6 +706,7 @@ static int dw8250_probe(struct platform_device *pdev)
p->dev = dev;
p->set_ldisc = dw8250_set_ldisc;
p->set_termios = dw8250_set_termios;
+ p->set_divisor = dw8250_set_divisor;
data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
if (!data)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index fa982e5cbe90..d5ea0f08a854 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -489,7 +489,7 @@ serial_port_out_sync(struct uart_port *p, int offset, int value)
/*
* FIFO support.
*/
-static void serial8250_clear_fifos(struct uart_8250_port *p)
+void serial8250_clear_fifos(struct uart_8250_port *p)
{
if (p->capabilities & UART_CAP_FIFO) {
serial_out(p, UART_FCR, UART_FCR_ENABLE_FIFO);
@@ -498,6 +498,7 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
serial_out(p, UART_FCR, 0);
}
}
+EXPORT_SYMBOL_GPL(serial8250_clear_fifos);
static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t);
static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t);
@@ -3200,6 +3201,17 @@ void serial8250_set_defaults(struct uart_8250_port *up)
}
EXPORT_SYMBOL_GPL(serial8250_set_defaults);
+void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count)
+{
+ unsigned int i;
+
+ for (i = 0; i < count; i++) {
+ if (wait_for_lsr(up, UART_LSR_THRE))
+ return;
+ }
+}
+EXPORT_SYMBOL_GPL(serial8250_fifo_wait_for_lsr_thre);
+
#ifdef CONFIG_SERIAL_8250_CONSOLE
static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
@@ -3241,16 +3253,6 @@ static void serial8250_console_restore(struct uart_8250_port *up)
serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
}
-static void fifo_wait_for_lsr(struct uart_8250_port *up, unsigned int count)
-{
- unsigned int i;
-
- for (i = 0; i < count; i++) {
- if (wait_for_lsr(up, UART_LSR_THRE))
- return;
- }
-}
-
/*
* Print a string to the serial port using the device FIFO
*
@@ -3269,7 +3271,7 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up,
while (s != end) {
/* Allow timeout for each byte of a possibly full FIFO */
- fifo_wait_for_lsr(up, fifosize);
+ serial8250_fifo_wait_for_lsr_thre(up, fifosize);
for (i = 0; i < fifosize && s != end; ++i) {
if (*s == '\n' && !cr_sent) {
@@ -3287,7 +3289,7 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up,
* Allow timeout for each byte written since the caller will only wait
* for UART_LSR_BOTH_EMPTY using the timeout of a single character
*/
- fifo_wait_for_lsr(up, tx_count);
+ serial8250_fifo_wait_for_lsr_thre(up, tx_count);
}
/*
--
2.39.5
^ permalink raw reply related
* Re: [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes
From: Andy Shevchenko @ 2026-01-23 21:41 UTC (permalink / raw)
To: Ilpo Järvinen
Cc: Greg Kroah-Hartman, Jiri Slaby, linux-serial, qianfan Zhao,
Adriana Nicolae, linux-kernel, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-3-ilpo.jarvinen@linux.intel.com>
On Fri, Jan 23, 2026 at 07:27:35PM +0200, Ilpo Järvinen wrote:
> When DW UART is configured with BUSY flag, LCR writes may not always
> succeed which can make any LCR write complex and very expensive.
> Performing write directly can trigger IRQ and the driver has to perform
> complex and distruptive sequence while retrying the write.
>
> Therefore, it's better to avoid doing LCR write that would not change
> the value of the LCR register. Add LCR write avoidance code into the
> 8250_dw driver's serial_out functions.
.serial_out() ?
...
> +/*
> + * With BUSY, LCR writes can be very expensive (IRQ + complex retry logic).
> + * If the write would not change the value of the LCR register, skip write
would --> does
skip write --> skip it
> + * entirely.
> + */
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply
* Re: [PATCH 3/6] serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling
From: Andy Shevchenko @ 2026-01-23 22:05 UTC (permalink / raw)
To: Ilpo Järvinen
Cc: Greg Kroah-Hartman, Jiri Slaby, linux-serial, qianfan Zhao,
Adriana Nicolae, linux-kernel, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-4-ilpo.jarvinen@linux.intel.com>
On Fri, Jan 23, 2026 at 07:27:36PM +0200, Ilpo Järvinen wrote:
> dw8250_handle_irq() takes port's lock multiple times with no good
> reason to release it in between and calls serial8250_handle_irq()
> that also takes port's lock.
>
> As serial8250_handle_irq() takes port's lock itself, create
> serial8250_handle_irq_locked() that allows caller to hold port's lock
> across the call. Take port's lock only once in dw8250_handle_irq() and
> call serial8250_handle_irq_locked() directly.
Sounds to me that the latter can be split to a prerequisite patch.
> As IIR_NO_INT check in serial8250_handle_irq() was outside of port's
> lock, it has to be done already in dw8250_handle_irq().
>
> DW UART can, in addition to IIR_NO_INT, report BUSY_DETECT (0x7) which
> collided with the IIR_NO_INT (0x1) check in serial8250_handle_irq()
> (because & is used instead of ==) meaning that no other work is done by
> serial8250_handle_irq() during an BUSY_DETECT interrupt.
>
> This allows reorganizing code in dw8250_handle_irq() to do both
> IIR_NO_INT and BUSY_DETECT handling right at the start simplifying
> the logic.
...
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
+ cleanup.h
> #include <linux/clk.h>
> #include <linux/delay.h>
> #include <linux/device.h>
...
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> #include <linux/ioport.h>
> #include <linux/init.h>
> #include <linux/irq.h>
> +#include <linux/lockdep.h>
I would still keep more order.
> #include <linux/console.h>
> #include <linux/gpio/consumer.h>
Giving the context we have, the better place for a new inclusion is somewhere
here.
> #include <linux/sysrq.h>
(Also perhaps sorting headers in a separate patch helps with finding better
places for the future inclusions?)
...
> +EXPORT_SYMBOL_GPL(serial8250_handle_irq_locked);
Wondering if we can start exporting with a namespace...
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply
* Re: [PATCH 4/6] serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm
From: Andy Shevchenko @ 2026-01-23 22:13 UTC (permalink / raw)
To: Ilpo Järvinen
Cc: Greg Kroah-Hartman, Jiri Slaby, linux-serial, qianfan Zhao,
Adriana Nicolae, linux-kernel, Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-5-ilpo.jarvinen@linux.intel.com>
On Fri, Jan 23, 2026 at 07:27:37PM +0200, Ilpo Järvinen wrote:
> INTC10EE UART can end up into an interrupt storm where it reports
> IIR_NO_INT (0x1). If the storm happens during active UART operation, it
> is promptly stopped by IIR value change due to Rx or Tx events.
> However, when there is no activity, either due to idle serial line or
> due to specific circumstances such as during shutdown that writes
> IER=0, there is nothing to stop the storm.
>
> During shutdown the storm is particularly problematic because
> serial8250_do_shutdown() calls synchronize_irq() that will hang in
> waiting for the storm to finish which never happens.
>
> This problem can also result in triggering a warning:
>
> irq 45: nobody cared (try booting with the "irqpoll" option)
> [...snip...]
> handlers:
> serial8250_interrupt
> Disabling IRQ #45
>
> Normal means to reset interrupt status by reading LSR, MSR, USR, or RX
> register do not result in the UART deasserting the IRQ.
>
> Add a quirk to INTC10EE UARTs to enable Tx interrupts if UART's Tx is
> currently empty and inactive. Rework IIR_NO_INT to keep track of the
> number of consecutive IIR_NO_INT, and on third one perform the quirk.
> Enabling Tx interrupts should change IIR value from IIR_NO_INT to
> IIR_THRI which has been observed to stop the storm.
...
> + u64 no_int_count;
Why so big?
...
> + d->no_int_count++;
> + if (d->no_int_count > 2 && quirks & DW_UART_QUIRK_IER_KICK)
> + dw8250_quirk_ier_kick(p);
Usual way is to use modulo. And perhaps use 4 for the sake of avoiding
division:
if (d->no_int_count == 3 && quirks & DW_UART_QUIRK_IER_KICK)
dw8250_quirk_ier_kick(p);
d->no_int_count = (d->no_int_count + 1) % 4;
where 4 may be defined with meaningful name. With that u8 is more than enough.
> return 0;
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply
* Re: [PATCH 6/6] serial: 8250_dw: Ensure BUSY is deasserted
From: Andy Shevchenko @ 2026-01-23 22:42 UTC (permalink / raw)
To: Ilpo Järvinen
Cc: Greg Kroah-Hartman, Jiri Slaby, linux-serial, qianfan Zhao,
Adriana Nicolae, Markus Mayer, Tim Kryger, Matt Porter,
Heikki Krogerus, Jamie Iles, linux-kernel, stable,
Bandal, Shankar, Murthy, Shanth
In-Reply-To: <20260123172739.13410-7-ilpo.jarvinen@linux.intel.com>
On Fri, Jan 23, 2026 at 07:27:39PM +0200, Ilpo Järvinen wrote:
> DW UART cannot write to LCR, DLL, and DLH while BUSY is asserted.
> Existance of BUSY depends on uart_16550_compatible, if UART HW is
> configured with 16550 compatible those registers can always be written.
with 16550 compatible --> with it
> There currently is dw8250_force_idle() which attempts to archive
> non-BUSY state by disabling FIFO, however, the solution is unreliable
> when Rx keeps getting more and more characters.
>
> Create a sequence of operations to enforce that ensures UART cannot
> keep BUSY asserted indefinitely. The new sequence relies on enabling
> loopback mode temporarily to prevent incoming Rx characters keeping
> UART BUSY.
What if UART was already in a loopback mode? I assume that Tx pause
described below should not affect the case.
The real case scenario that I am thinking of is a stress test of UART
using loopback mode.
> Ensure no Tx in ongoing while the UART is switches into the loopback
> mode (requires exporting serial8250_fifo_wait_for_lsr_thre() and adding
> DMA Tx pause/resume functions).
>
> According to tests performed by Adriana Nicolae <adriana@arista.com>,
> simply disabling FIFO or clearing FIFOs only once does not always
> ensure BUSY is deasserted but up to two tries may be needed. This could
> be related to ongoing Rx of a character (a guess, not known for sure).
Sounds like a plausible theory because UART has shift registers that are
working independently on the current situation with FIFO. They are actual
frontends for Tx and Rx data on the wire.
> Therefore, retry FIFO clearing a few times (retry limit 4 is arbitrary
> number but using, e.g., p->fifosize seems overly large). Tests
> performed by others did not exhibit similar challenge but it does not
> seem harmful to leave the FIFO clearing loop in place for all DW UARTs
> with BUSY functionality.
>
> Use the new dw8250_idle_enter/exit() to do divisor writes and LCR
> writes. In case of plain LCR writes, opportunistically try to update
> LCR first and only invoke dw8250_idle_enter() if the write did not
> succeed (it has been observed that in practice most LCR writes do
> succeed without complications).
>
> This issue was first reported by qianfan Zhao who put lots of debugging
> effort into understanding the solution space.
...
> + /* Prevent triggering interrupt from RBR filling */
> + p->serial_out(p, UART_IER, 0);
Do we specifically use callbacks directly and not wrappers all over the change?
...
> + serial8250_fifo_wait_for_lsr_thre(up, p->fifosize);
> + ndelay(p->frame_time);
Wouldn't be a problem on lowest baud rates (exempli gratia 110)?
...
> + retries = 4; /* Arbitrary limit, 2 was always enough in tests */
> + do {
> + serial8250_clear_fifos(up);
> + if (!(p->serial_in(p, usr_reg) & DW_UART_USR_BUSY))
> + break;
> + ndelay(p->frame_time);
> + } while (--retries);
read_poll_timeout_atomic() ? I assume it can't be used due to small frame time?
...
> + if (d->in_idle) {
> + /*
> + * FIXME: this deadlocks if port->lock is already held
> + * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
> + */
Hmm... That FIXME should gone since we have non-blocking consoles, no?
> + return;
> + }
...
> + ret = dw8250_idle_enter(p);
> + if (ret < 0) {
> + /*
> + * FIXME: this deadlocks if port->lock is already held
> + * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
> + */
> + goto idle_failed;
> }
> - /*
> - * FIXME: this deadlocks if port->lock is already held
> - * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
> - */
Ditto.
> }
...
> p->dev = dev;
Maybe put an added line here?
> p->set_ldisc = dw8250_set_ldisc;
> p->set_termios = dw8250_set_termios;
> + p->set_divisor = dw8250_set_divisor;
...
> +EXPORT_SYMBOL_GPL(serial8250_clear_fifos);
Same Q, perhaps start exporting with a namespace?
> }
> EXPORT_SYMBOL_GPL(serial8250_set_defaults);
...
> +void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count)
> +{
> + unsigned int i;
> +
> + for (i = 0; i < count; i++) {
while (count--) ?
Ah, it's existing code... OK then.
> + if (wait_for_lsr(up, UART_LSR_THRE))
> + return;
> + }
> +}
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply
* [tty:tty-testing] BUILD SUCCESS d000422a46aad32217cf1be747eb61d641baae2f
From: kernel test robot @ 2026-01-24 4:38 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: linux-serial
tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing
branch HEAD: d000422a46aad32217cf1be747eb61d641baae2f tty: tty_port: add workqueue to flip TTY buffer
elapsed time: 729m
configs tested: 204
configs skipped: 2
The following configs have been built successfully.
More configs may be tested in the coming days.
tested configs:
alpha allnoconfig gcc-15.2.0
alpha allyesconfig gcc-15.2.0
alpha defconfig gcc-15.2.0
arc allmodconfig clang-16
arc allnoconfig gcc-15.2.0
arc allyesconfig clang-22
arc axs103_smp_defconfig gcc-15.2.0
arc defconfig gcc-15.2.0
arc randconfig-001-20260124 clang-18
arc randconfig-002-20260124 clang-18
arm allnoconfig clang-22
arm allnoconfig gcc-15.2.0
arm allyesconfig clang-16
arm defconfig gcc-15.2.0
arm gemini_defconfig gcc-15.2.0
arm imx_v4_v5_defconfig gcc-15.2.0
arm multi_v4t_defconfig clang-16
arm pxa168_defconfig clang-16
arm randconfig-001-20260124 clang-18
arm randconfig-002-20260124 clang-18
arm randconfig-003-20260124 clang-18
arm randconfig-004-20260124 clang-18
arm sama7_defconfig clang-16
arm spear3xx_defconfig gcc-15.2.0
arm versatile_defconfig gcc-15.2.0
arm vt8500_v6_v7_defconfig gcc-15.2.0
arm64 allmodconfig clang-22
arm64 allnoconfig gcc-15.2.0
arm64 defconfig gcc-15.2.0
arm64 randconfig-001-20260124 gcc-15.2.0
arm64 randconfig-002-20260124 gcc-15.2.0
arm64 randconfig-003-20260124 gcc-15.2.0
arm64 randconfig-004-20260124 gcc-15.2.0
csky allmodconfig gcc-15.2.0
csky allnoconfig gcc-15.2.0
csky defconfig gcc-15.2.0
csky randconfig-001-20260124 gcc-15.2.0
csky randconfig-002-20260124 gcc-15.2.0
hexagon allmodconfig gcc-15.2.0
hexagon allnoconfig clang-22
hexagon allnoconfig gcc-15.2.0
hexagon defconfig gcc-15.2.0
hexagon randconfig-001-20260124 gcc-15.2.0
hexagon randconfig-002-20260124 gcc-15.2.0
i386 alldefconfig clang-16
i386 allmodconfig clang-20
i386 allnoconfig gcc-14
i386 allnoconfig gcc-15.2.0
i386 allyesconfig clang-20
i386 buildonly-randconfig-001-20260124 gcc-14
i386 buildonly-randconfig-002-20260124 gcc-14
i386 buildonly-randconfig-003-20260124 gcc-14
i386 buildonly-randconfig-004-20260124 gcc-14
i386 buildonly-randconfig-005-20260124 gcc-14
i386 buildonly-randconfig-006-20260124 gcc-14
i386 defconfig gcc-15.2.0
i386 randconfig-001-20260124 gcc-14
i386 randconfig-002-20260124 gcc-14
i386 randconfig-003-20260124 gcc-14
i386 randconfig-004-20260124 gcc-14
i386 randconfig-005-20260124 gcc-14
i386 randconfig-006-20260124 gcc-14
i386 randconfig-007-20260124 gcc-14
i386 randconfig-011-20260124 clang-20
i386 randconfig-012-20260124 clang-20
i386 randconfig-013-20260124 clang-20
i386 randconfig-014-20260124 clang-20
i386 randconfig-015-20260124 clang-20
i386 randconfig-016-20260124 clang-20
i386 randconfig-017-20260124 clang-20
loongarch allmodconfig clang-22
loongarch allnoconfig clang-22
loongarch allnoconfig gcc-15.2.0
loongarch defconfig clang-19
loongarch randconfig-001-20260124 gcc-15.2.0
loongarch randconfig-002-20260124 gcc-15.2.0
m68k allmodconfig gcc-15.2.0
m68k allnoconfig gcc-15.2.0
m68k allyesconfig clang-16
m68k defconfig clang-19
m68k m5475evb_defconfig gcc-15.2.0
m68k virt_defconfig gcc-15.2.0
microblaze allnoconfig gcc-15.2.0
microblaze allyesconfig gcc-15.2.0
microblaze defconfig clang-19
mips allmodconfig gcc-15.2.0
mips allnoconfig gcc-15.2.0
mips allyesconfig gcc-15.2.0
mips malta_qemu_32r6_defconfig clang-16
mips maltasmvp_eva_defconfig gcc-15.2.0
mips maltaup_defconfig gcc-15.2.0
mips maltaup_xpa_defconfig gcc-15.2.0
mips qi_lb60_defconfig clang-16
nios2 allmodconfig clang-22
nios2 allnoconfig clang-22
nios2 allnoconfig gcc-11.5.0
nios2 defconfig clang-19
nios2 randconfig-001-20260124 gcc-15.2.0
nios2 randconfig-002-20260124 gcc-15.2.0
openrisc allmodconfig clang-22
openrisc allnoconfig clang-22
openrisc allnoconfig gcc-15.2.0
openrisc defconfig gcc-15.2.0
parisc allmodconfig gcc-15.2.0
parisc allnoconfig clang-22
parisc allnoconfig gcc-15.2.0
parisc allyesconfig clang-19
parisc defconfig gcc-15.2.0
parisc randconfig-001-20260124 gcc-8.5.0
parisc randconfig-002-20260124 gcc-8.5.0
parisc64 defconfig clang-19
powerpc allmodconfig gcc-15.2.0
powerpc allnoconfig clang-22
powerpc allnoconfig gcc-15.2.0
powerpc motionpro_defconfig gcc-15.2.0
powerpc ppa8548_defconfig gcc-15.2.0
powerpc randconfig-001-20260124 gcc-8.5.0
powerpc randconfig-002-20260124 gcc-8.5.0
powerpc64 randconfig-001-20260124 gcc-8.5.0
powerpc64 randconfig-002-20260124 gcc-8.5.0
riscv allmodconfig clang-22
riscv allnoconfig clang-22
riscv allnoconfig gcc-15.2.0
riscv allyesconfig clang-16
riscv defconfig gcc-15.2.0
riscv randconfig-001-20260124 gcc-8.5.0
riscv randconfig-002-20260124 gcc-8.5.0
s390 allmodconfig clang-19
s390 allnoconfig clang-22
s390 allyesconfig gcc-15.2.0
s390 defconfig gcc-15.2.0
s390 randconfig-001-20260124 gcc-8.5.0
s390 randconfig-002-20260124 gcc-8.5.0
sh allmodconfig gcc-15.2.0
sh allnoconfig clang-22
sh allnoconfig gcc-15.2.0
sh allyesconfig clang-19
sh defconfig gcc-14
sh edosk7705_defconfig gcc-15.2.0
sh r7780mp_defconfig clang-16
sh randconfig-001-20260124 gcc-8.5.0
sh randconfig-002-20260124 gcc-8.5.0
sh secureedge5410_defconfig clang-16
sparc allnoconfig clang-22
sparc allnoconfig gcc-15.2.0
sparc defconfig gcc-15.2.0
sparc randconfig-001-20260124 gcc-13.4.0
sparc randconfig-002-20260124 gcc-13.4.0
sparc sparc64_defconfig gcc-15.2.0
sparc64 allmodconfig clang-22
sparc64 defconfig gcc-14
sparc64 randconfig-001-20260124 gcc-13.4.0
sparc64 randconfig-002-20260124 gcc-13.4.0
um allmodconfig clang-19
um allnoconfig clang-22
um allyesconfig gcc-15.2.0
um defconfig gcc-14
um i386_defconfig gcc-14
um randconfig-001-20260124 gcc-13.4.0
um randconfig-002-20260124 gcc-13.4.0
um x86_64_defconfig gcc-14
x86_64 alldefconfig gcc-15.2.0
x86_64 allmodconfig clang-20
x86_64 allnoconfig clang-20
x86_64 allnoconfig clang-22
x86_64 allyesconfig clang-20
x86_64 buildonly-randconfig-001-20260124 clang-20
x86_64 buildonly-randconfig-002-20260124 clang-20
x86_64 buildonly-randconfig-003-20260124 clang-20
x86_64 buildonly-randconfig-004-20260124 clang-20
x86_64 buildonly-randconfig-005-20260124 clang-20
x86_64 buildonly-randconfig-006-20260124 clang-20
x86_64 defconfig gcc-14
x86_64 kexec clang-20
x86_64 randconfig-001-20260124 gcc-13
x86_64 randconfig-002-20260124 gcc-13
x86_64 randconfig-003-20260124 gcc-13
x86_64 randconfig-004-20260124 gcc-13
x86_64 randconfig-005-20260124 gcc-13
x86_64 randconfig-006-20260124 gcc-13
x86_64 randconfig-011-20260124 gcc-12
x86_64 randconfig-012-20260124 gcc-12
x86_64 randconfig-013-20260124 gcc-12
x86_64 randconfig-014-20260124 gcc-12
x86_64 randconfig-015-20260124 gcc-12
x86_64 randconfig-016-20260124 gcc-12
x86_64 randconfig-071-20260124 gcc-14
x86_64 randconfig-072-20260124 gcc-14
x86_64 randconfig-073-20260124 gcc-14
x86_64 randconfig-074-20260124 gcc-14
x86_64 randconfig-075-20260124 gcc-14
x86_64 randconfig-076-20260124 gcc-14
x86_64 rhel-9.4 clang-20
x86_64 rhel-9.4-bpf gcc-14
x86_64 rhel-9.4-func clang-20
x86_64 rhel-9.4-kselftests clang-20
x86_64 rhel-9.4-kunit gcc-14
x86_64 rhel-9.4-ltp gcc-14
x86_64 rhel-9.4-rust clang-20
xtensa allnoconfig clang-22
xtensa allnoconfig gcc-15.2.0
xtensa allyesconfig clang-22
xtensa randconfig-001-20260124 gcc-13.4.0
xtensa randconfig-002-20260124 gcc-13.4.0
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply
* [tty:tty-linus] BUILD SUCCESS 32f37e57583f869140cff445feedeea8a5fea986
From: kernel test robot @ 2026-01-24 4:39 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: linux-serial
tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-linus
branch HEAD: 32f37e57583f869140cff445feedeea8a5fea986 serial: Fix not set tty->port race condition
elapsed time: 730m
configs tested: 204
configs skipped: 2
The following configs have been built successfully.
More configs may be tested in the coming days.
tested configs:
alpha allnoconfig gcc-15.2.0
alpha allyesconfig gcc-15.2.0
alpha defconfig gcc-15.2.0
arc allmodconfig clang-16
arc allnoconfig gcc-15.2.0
arc allyesconfig clang-22
arc axs103_smp_defconfig gcc-15.2.0
arc defconfig gcc-15.2.0
arc randconfig-001-20260124 clang-18
arc randconfig-002-20260124 clang-18
arm allnoconfig clang-22
arm allnoconfig gcc-15.2.0
arm allyesconfig clang-16
arm defconfig gcc-15.2.0
arm gemini_defconfig gcc-15.2.0
arm imx_v4_v5_defconfig gcc-15.2.0
arm multi_v4t_defconfig clang-16
arm pxa168_defconfig clang-16
arm randconfig-001-20260124 clang-18
arm randconfig-002-20260124 clang-18
arm randconfig-003-20260124 clang-18
arm randconfig-004-20260124 clang-18
arm sama7_defconfig clang-16
arm spear3xx_defconfig gcc-15.2.0
arm versatile_defconfig gcc-15.2.0
arm vt8500_v6_v7_defconfig gcc-15.2.0
arm64 allmodconfig clang-22
arm64 allnoconfig gcc-15.2.0
arm64 defconfig gcc-15.2.0
arm64 randconfig-001-20260124 gcc-15.2.0
arm64 randconfig-002-20260124 gcc-15.2.0
arm64 randconfig-003-20260124 gcc-15.2.0
arm64 randconfig-004-20260124 gcc-15.2.0
csky allmodconfig gcc-15.2.0
csky allnoconfig gcc-15.2.0
csky defconfig gcc-15.2.0
csky randconfig-001-20260124 gcc-15.2.0
csky randconfig-002-20260124 gcc-15.2.0
hexagon allmodconfig gcc-15.2.0
hexagon allnoconfig clang-22
hexagon allnoconfig gcc-15.2.0
hexagon defconfig gcc-15.2.0
hexagon randconfig-001-20260124 gcc-15.2.0
hexagon randconfig-002-20260124 gcc-15.2.0
i386 alldefconfig clang-16
i386 allmodconfig clang-20
i386 allnoconfig gcc-14
i386 allnoconfig gcc-15.2.0
i386 allyesconfig clang-20
i386 buildonly-randconfig-001-20260124 gcc-14
i386 buildonly-randconfig-002-20260124 gcc-14
i386 buildonly-randconfig-003-20260124 gcc-14
i386 buildonly-randconfig-004-20260124 gcc-14
i386 buildonly-randconfig-005-20260124 gcc-14
i386 buildonly-randconfig-006-20260124 gcc-14
i386 defconfig gcc-15.2.0
i386 randconfig-001-20260124 gcc-14
i386 randconfig-002-20260124 gcc-14
i386 randconfig-003-20260124 gcc-14
i386 randconfig-004-20260124 gcc-14
i386 randconfig-005-20260124 gcc-14
i386 randconfig-006-20260124 gcc-14
i386 randconfig-007-20260124 gcc-14
i386 randconfig-011-20260124 clang-20
i386 randconfig-012-20260124 clang-20
i386 randconfig-013-20260124 clang-20
i386 randconfig-014-20260124 clang-20
i386 randconfig-015-20260124 clang-20
i386 randconfig-016-20260124 clang-20
i386 randconfig-017-20260124 clang-20
loongarch allmodconfig clang-22
loongarch allnoconfig clang-22
loongarch allnoconfig gcc-15.2.0
loongarch defconfig clang-19
loongarch randconfig-001-20260124 gcc-15.2.0
loongarch randconfig-002-20260124 gcc-15.2.0
m68k allmodconfig gcc-15.2.0
m68k allnoconfig gcc-15.2.0
m68k allyesconfig clang-16
m68k defconfig clang-19
m68k m5475evb_defconfig gcc-15.2.0
m68k virt_defconfig gcc-15.2.0
microblaze allnoconfig gcc-15.2.0
microblaze allyesconfig gcc-15.2.0
microblaze defconfig clang-19
mips allmodconfig gcc-15.2.0
mips allnoconfig gcc-15.2.0
mips allyesconfig gcc-15.2.0
mips malta_qemu_32r6_defconfig clang-16
mips maltasmvp_eva_defconfig gcc-15.2.0
mips maltaup_defconfig gcc-15.2.0
mips maltaup_xpa_defconfig gcc-15.2.0
mips qi_lb60_defconfig clang-16
nios2 allmodconfig clang-22
nios2 allnoconfig clang-22
nios2 allnoconfig gcc-11.5.0
nios2 defconfig clang-19
nios2 randconfig-001-20260124 gcc-15.2.0
nios2 randconfig-002-20260124 gcc-15.2.0
openrisc allmodconfig clang-22
openrisc allnoconfig clang-22
openrisc allnoconfig gcc-15.2.0
openrisc defconfig gcc-15.2.0
parisc allmodconfig gcc-15.2.0
parisc allnoconfig clang-22
parisc allnoconfig gcc-15.2.0
parisc allyesconfig clang-19
parisc defconfig gcc-15.2.0
parisc randconfig-001-20260124 gcc-8.5.0
parisc randconfig-002-20260124 gcc-8.5.0
parisc64 defconfig clang-19
powerpc allmodconfig gcc-15.2.0
powerpc allnoconfig clang-22
powerpc allnoconfig gcc-15.2.0
powerpc motionpro_defconfig gcc-15.2.0
powerpc ppa8548_defconfig gcc-15.2.0
powerpc randconfig-001-20260124 gcc-8.5.0
powerpc randconfig-002-20260124 gcc-8.5.0
powerpc64 randconfig-001-20260124 gcc-8.5.0
powerpc64 randconfig-002-20260124 gcc-8.5.0
riscv allmodconfig clang-22
riscv allnoconfig clang-22
riscv allnoconfig gcc-15.2.0
riscv allyesconfig clang-16
riscv defconfig gcc-15.2.0
riscv randconfig-001-20260124 gcc-8.5.0
riscv randconfig-002-20260124 gcc-8.5.0
s390 allmodconfig clang-19
s390 allnoconfig clang-22
s390 allyesconfig gcc-15.2.0
s390 defconfig gcc-15.2.0
s390 randconfig-001-20260124 gcc-8.5.0
s390 randconfig-002-20260124 gcc-8.5.0
sh allmodconfig gcc-15.2.0
sh allnoconfig clang-22
sh allnoconfig gcc-15.2.0
sh allyesconfig clang-19
sh defconfig gcc-14
sh edosk7705_defconfig gcc-15.2.0
sh r7780mp_defconfig clang-16
sh randconfig-001-20260124 gcc-8.5.0
sh randconfig-002-20260124 gcc-8.5.0
sh secureedge5410_defconfig clang-16
sparc allnoconfig clang-22
sparc allnoconfig gcc-15.2.0
sparc defconfig gcc-15.2.0
sparc randconfig-001-20260124 gcc-13.4.0
sparc randconfig-002-20260124 gcc-13.4.0
sparc sparc64_defconfig gcc-15.2.0
sparc64 allmodconfig clang-22
sparc64 defconfig gcc-14
sparc64 randconfig-001-20260124 gcc-13.4.0
sparc64 randconfig-002-20260124 gcc-13.4.0
um allmodconfig clang-19
um allnoconfig clang-22
um allyesconfig gcc-15.2.0
um defconfig gcc-14
um i386_defconfig gcc-14
um randconfig-001-20260124 gcc-13.4.0
um randconfig-002-20260124 gcc-13.4.0
um x86_64_defconfig gcc-14
x86_64 alldefconfig gcc-15.2.0
x86_64 allmodconfig clang-20
x86_64 allnoconfig clang-20
x86_64 allnoconfig clang-22
x86_64 allyesconfig clang-20
x86_64 buildonly-randconfig-001-20260124 clang-20
x86_64 buildonly-randconfig-002-20260124 clang-20
x86_64 buildonly-randconfig-003-20260124 clang-20
x86_64 buildonly-randconfig-004-20260124 clang-20
x86_64 buildonly-randconfig-005-20260124 clang-20
x86_64 buildonly-randconfig-006-20260124 clang-20
x86_64 defconfig gcc-14
x86_64 kexec clang-20
x86_64 randconfig-001-20260124 gcc-13
x86_64 randconfig-002-20260124 gcc-13
x86_64 randconfig-003-20260124 gcc-13
x86_64 randconfig-004-20260124 gcc-13
x86_64 randconfig-005-20260124 gcc-13
x86_64 randconfig-006-20260124 gcc-13
x86_64 randconfig-011-20260124 gcc-12
x86_64 randconfig-012-20260124 gcc-12
x86_64 randconfig-013-20260124 gcc-12
x86_64 randconfig-014-20260124 gcc-12
x86_64 randconfig-015-20260124 gcc-12
x86_64 randconfig-016-20260124 gcc-12
x86_64 randconfig-071-20260124 gcc-14
x86_64 randconfig-072-20260124 gcc-14
x86_64 randconfig-073-20260124 gcc-14
x86_64 randconfig-074-20260124 gcc-14
x86_64 randconfig-075-20260124 gcc-14
x86_64 randconfig-076-20260124 gcc-14
x86_64 rhel-9.4 clang-20
x86_64 rhel-9.4-bpf gcc-14
x86_64 rhel-9.4-func clang-20
x86_64 rhel-9.4-kselftests clang-20
x86_64 rhel-9.4-kunit gcc-14
x86_64 rhel-9.4-ltp gcc-14
x86_64 rhel-9.4-rust clang-20
xtensa allnoconfig clang-22
xtensa allnoconfig gcc-15.2.0
xtensa allyesconfig clang-22
xtensa randconfig-001-20260124 gcc-13.4.0
xtensa randconfig-002-20260124 gcc-13.4.0
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply
* [GIT PULL] Serial driver fixes for 6.19-rc7
From: Greg KH @ 2026-01-25 15:23 UTC (permalink / raw)
To: Linus Torvalds
Cc: Jiri Slaby, Stephen Rothwell, Andrew Morton, linux-kernel,
linux-serial
The following changes since commit f8f9c1f4d0c7a64600e2ca312dec824a0bc2f1da:
Linux 6.19-rc3 (2025-12-28 13:24:26 -0800)
are available in the Git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tags/tty-6.19-rc7
for you to fetch changes up to 32f37e57583f869140cff445feedeea8a5fea986:
serial: Fix not set tty->port race condition (2026-01-23 17:23:09 +0100)
----------------------------------------------------------------
Serial driver fixes for 6.19-rc7
Here are 3 small serial driver fixes for 6.19-rc7 that resolve some
reported issues. They include:
- tty->port race condition fix for a reported problem
- qcom_geni serial driver fix
- 8250_pci serial driver fix
All of these have been in linux-next with no reported issues
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
----------------------------------------------------------------
Krzysztof Kozlowski (1):
serial: Fix not set tty->port race condition
Marnix Rijnart (1):
serial: 8250_pci: Fix broken RS485 for F81504/508/512
Praveen Talari (1):
serial: qcom_geni: Fix BT failure regression on RB2 platform
drivers/tty/serial/8250/8250_pci.c | 2 +-
drivers/tty/serial/qcom_geni_serial.c | 13 ++++++-------
drivers/tty/serial/serial_core.c | 6 ++++++
3 files changed, 13 insertions(+), 8 deletions(-)
^ permalink raw reply
* Re: [GIT PULL] Serial driver fixes for 6.19-rc7
From: pr-tracker-bot @ 2026-01-25 18:05 UTC (permalink / raw)
To: Greg KH
Cc: Linus Torvalds, Jiri Slaby, Stephen Rothwell, Andrew Morton,
linux-kernel, linux-serial
In-Reply-To: <aXY1f0U7rHgwl4bO@kroah.com>
The pull request you sent on Sun, 25 Jan 2026 16:23:43 +0100:
> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tags/tty-6.19-rc7
has been merged into torvalds/linux.git:
https://git.kernel.org/torvalds/c/11de40c03cf0f84466f517cc4d58f02ff1ba30be
Thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/prtracker.html
^ permalink raw reply
* [syzbot] [serial?] KMSAN: uninit-value in gsmld_receive_buf (2)
From: syzbot @ 2026-01-26 5:31 UTC (permalink / raw)
To: gregkh, jirislaby, linux-kernel, linux-serial, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: cf38b2340c0e Merge tag 'soc-fixes-6.19-2' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e05d22580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=60e074cc0d3b54a82cf1
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0bca22500a65/disk-cf38b234.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7d7caf81eafb/vmlinux-cf38b234.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d9e3619531e9/bzImage-cf38b234.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+60e074cc0d3b54a82cf1@syzkaller.appspotmail.com
=====================================================
BUG: KMSAN: uninit-value in gsmld_receive_buf+0x558/0x5d0 drivers/tty/n_gsm.c:3617
gsmld_receive_buf+0x558/0x5d0 drivers/tty/n_gsm.c:3617
tty_ldisc_receive_buf+0x1f7/0x2c0 drivers/tty/tty_buffer.c:391
tty_port_default_receive_buf+0xd7/0x1a0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x43e/0xe40 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0xb03/0x1da0 kernel/workqueue.c:3340
worker_thread+0xede/0x1590 kernel/workqueue.c:3421
kthread+0xd5a/0xf00 kernel/kthread.c:463
ret_from_fork+0x207/0x6f0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
Uninit was created at:
slab_post_alloc_hook mm/slub.c:4960 [inline]
slab_alloc_node mm/slub.c:5263 [inline]
__do_kmalloc_node mm/slub.c:5656 [inline]
__kmalloc_noprof+0xae9/0x1c00 mm/slub.c:5669
kmalloc_noprof include/linux/slab.h:961 [inline]
tty_buffer_alloc drivers/tty/tty_buffer.c:180 [inline]
__tty_buffer_request_room+0x3d4/0x7a0 drivers/tty/tty_buffer.c:273
__tty_insert_flip_string_flags+0x157/0x6f0 drivers/tty/tty_buffer.c:309
tty_insert_flip_char include/linux/tty_flip.h:77 [inline]
uart_insert_char+0x368/0x930 drivers/tty/serial/serial_core.c:3423
serial8250_read_char+0x1ba/0x670 drivers/tty/serial/8250/8250_port.c:1641
serial8250_rx_chars drivers/tty/serial/8250/8250_port.c:1658 [inline]
serial8250_handle_irq+0x930/0x1110 drivers/tty/serial/8250/8250_port.c:1822
serial8250_default_handle_irq+0x116/0x370 drivers/tty/serial/8250/8250_port.c:1846
serial8250_interrupt+0xcb/0x420 drivers/tty/serial/8250/8250_core.c:86
__handle_irq_event_percpu+0x118/0xec0 kernel/irq/handle.c:211
handle_irq_event_percpu kernel/irq/handle.c:248 [inline]
handle_irq_event+0xe0/0x2a0 kernel/irq/handle.c:265
handle_edge_irq+0x2a9/0xb50 kernel/irq/chip.c:855
generic_handle_irq_desc include/linux/irqdesc.h:172 [inline]
handle_irq arch/x86/kernel/irq.c:255 [inline]
call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
__common_interrupt+0x9d/0x180 arch/x86/kernel/irq.c:326
common_interrupt+0x94/0xb0 arch/x86/kernel/irq.c:319
asm_common_interrupt+0x2b/0x40 arch/x86/include/asm/idtentry.h:688
CPU: 1 UID: 0 PID: 6065 Comm: kworker/u8:16 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound flush_to_ldisc
=====================================================
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
^ permalink raw reply
* [PATCH] vt: Add enable module parameter
From: Jocelyn Falempe @ 2026-01-26 9:21 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, Nicolas Pitre, Calixte Pernot,
linux-kernel, linux-serial
Cc: Jocelyn Falempe
This allows to build the kernel with CONFIG_VT enabled, and choose
on the kernel command line to enable it or not.
Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
---
drivers/tty/Kconfig | 13 +++++++++++++
drivers/tty/vt/vt.c | 5 +++++
2 files changed, 18 insertions(+)
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 149f3d53b7608..2b94c2710687a 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -41,6 +41,19 @@ config VT
If unsure, say Y, or else you won't be able to do much with your new
shiny Linux system :-)
+config VT_ENABLE
+ depends on VT
+ default y
+ bool "enable VT terminal" if EXPERT
+ help
+ This allows to build the kernel with CONFIG_VT, and choose on the
+ kernel command line to enable it or not. If set to y, VT will be
+ enabled by default, but can be disabled with vt.enable=0 on the kernel
+ command line. Otherwise, use vt.enable=1 to enable VT.
+ This should help to transition to VT-less system.
+
+ If unsure, say Y.
+
config CONSOLE_TRANSLATIONS
depends on VT
default y
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 59b4b5e126ba1..d83613d98f594 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -164,6 +164,8 @@ EXPORT_SYMBOL(global_cursor_default);
static int cur_default = CUR_UNDERLINE;
module_param(cur_default, int, S_IRUGO | S_IWUSR);
+static bool vt_enable = IS_ENABLED(CONFIG_VT_ENABLE) ? true : false;
+module_param_named(enable, vt_enable, bool, S_IRUGO | S_IWUSR);
/*
* ignore_poke: don't unblank the screen when things are typed. This is
@@ -3852,6 +3854,9 @@ ATTRIBUTE_GROUPS(vt_dev);
int __init vty_init(const struct file_operations *console_fops)
{
+ if (!vt_enable)
+ return 0;
+
cdev_init(&vc0_cdev, console_fops);
if (cdev_add(&vc0_cdev, MKDEV(TTY_MAJOR, 0), 1) ||
register_chrdev_region(MKDEV(TTY_MAJOR, 0), 1, "/dev/vc/0") < 0)
base-commit: 24d479d26b25bce5faea3ddd9fa8f3a6c3129ea7
--
2.52.0
^ permalink raw reply related
* Re: [PATCH] vt: Add enable module parameter
From: Greg Kroah-Hartman @ 2026-01-26 9:33 UTC (permalink / raw)
To: Jocelyn Falempe
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <20260126092234.713465-1-jfalempe@redhat.com>
On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
> This allows to build the kernel with CONFIG_VT enabled, and choose
> on the kernel command line to enable it or not.
This says what is happening, but not why?
> Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
Why are we using a 1990's technology for a new feature? What is this
going to allow to have happen? Who needs/wants this? Who will use it?
For what?
> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
> ---
> drivers/tty/Kconfig | 13 +++++++++++++
> drivers/tty/vt/vt.c | 5 +++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index 149f3d53b7608..2b94c2710687a 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -41,6 +41,19 @@ config VT
> If unsure, say Y, or else you won't be able to do much with your new
> shiny Linux system :-)
>
> +config VT_ENABLE
> + depends on VT
> + default y
> + bool "enable VT terminal" if EXPERT
So no one will ever really use this config option?
And you are doing 2 things in this patch, not just one, unlike what the
changelog said :(
thanks,
greg k-h
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Jocelyn Falempe @ 2026-01-26 9:43 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <2026012613-cotton-jellied-b67a@gregkh>
On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
> On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
>> This allows to build the kernel with CONFIG_VT enabled, and choose
>> on the kernel command line to enable it or not.
>
> This says what is happening, but not why?
>
>> Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
>
> Why are we using a 1990's technology for a new feature? What is this
> going to allow to have happen? Who needs/wants this? Who will use it?
> For what?
The goal is to ease the transition to disable CONFIG_VT.
So if this is merged, you can boot without VT on any Linux distribution,
without rebuilding the kernel.
This option will also allow a distribution to disable VT by default, but
users that really wants this can enable it on the kernel command line,
without rebuilding the kernel.
It will also avoid hacky solution in userspace like this:
https://overhead.neocities.org/blog/systemd-logind-seat/#very-hacky-solutions
>
>> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
>> ---
>> drivers/tty/Kconfig | 13 +++++++++++++
>> drivers/tty/vt/vt.c | 5 +++++
>> 2 files changed, 18 insertions(+)
>>
>> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
>> index 149f3d53b7608..2b94c2710687a 100644
>> --- a/drivers/tty/Kconfig
>> +++ b/drivers/tty/Kconfig
>> @@ -41,6 +41,19 @@ config VT
>> If unsure, say Y, or else you won't be able to do much with your new
>> shiny Linux system :-)
>>
>> +config VT_ENABLE
>> + depends on VT
>> + default y
>> + bool "enable VT terminal" if EXPERT
>
> So no one will ever really use this config option?
>
> And you are doing 2 things in this patch, not just one, unlike what the
> changelog said :(
I can split that in two if you prefer.
Adding a module parameter, and adding a Kconfig option, to choose the
default for this module parameter.
>
> thanks,
>
> greg k-h
>
--
Jocelyn
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Greg Kroah-Hartman @ 2026-01-26 10:20 UTC (permalink / raw)
To: Jocelyn Falempe
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <48be84fb-bee4-4a22-bde4-0d0c78282f80@redhat.com>
On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
> On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
> > On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
> > > This allows to build the kernel with CONFIG_VT enabled, and choose
> > > on the kernel command line to enable it or not.
> >
> > This says what is happening, but not why?
> >
> > > Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
> >
> > Why are we using a 1990's technology for a new feature? What is this
> > going to allow to have happen? Who needs/wants this? Who will use it?
> > For what?
>
> The goal is to ease the transition to disable CONFIG_VT.
>
> So if this is merged, you can boot without VT on any Linux distribution,
> without rebuilding the kernel.
But that's a distro-specific thing, the distro should be enabling or
disabling the option as it needs, it should not be a user-configurable
boot-time selection option as userspace depends entirely on this either
being there or not. Why would you have a kernel with both options but
userspace without that?
> This option will also allow a distribution to disable VT by default, but
> users that really wants this can enable it on the kernel command line,
> without rebuilding the kernel.
Why would a user want that? If a user really wants it enabled, why
would userspace even still work and why would they want to not rebuild
the kernel?
> It will also avoid hacky solution in userspace like this:
> https://overhead.neocities.org/blog/systemd-logind-seat/#very-hacky-solutions
Surely that can't be the only way, why can't userspace just handle this
"properly" if it wants to?
> > > Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
> > > ---
> > > drivers/tty/Kconfig | 13 +++++++++++++
> > > drivers/tty/vt/vt.c | 5 +++++
> > > 2 files changed, 18 insertions(+)
> > >
> > > diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> > > index 149f3d53b7608..2b94c2710687a 100644
> > > --- a/drivers/tty/Kconfig
> > > +++ b/drivers/tty/Kconfig
> > > @@ -41,6 +41,19 @@ config VT
> > > If unsure, say Y, or else you won't be able to do much with your new
> > > shiny Linux system :-)
> > > +config VT_ENABLE
> > > + depends on VT
> > > + default y
> > > + bool "enable VT terminal" if EXPERT
> >
> > So no one will ever really use this config option?
> >
> > And you are doing 2 things in this patch, not just one, unlike what the
> > changelog said :(
>
> I can split that in two if you prefer.
I'm objecting to the patch doing something other than what the changelog
describes, which as you know is not a good thing.
> Adding a module parameter, and adding a Kconfig option, to choose the
> default for this module parameter.
I really don't like adding new module parameters that we are going to
have to now support for forever. Why not just rely on the config option
being there or not as-is? That's why we allowed it to be turned off at
all, because userspace was going to be moved to not need it anymore.
Why would we want to support "both" at the same time in the kernel?
thanks,
greg k-h
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Greg Kroah-Hartman @ 2026-01-26 10:30 UTC (permalink / raw)
To: Jocelyn Falempe
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <2026012648-vantage-mummified-2a43@gregkh>
On Mon, Jan 26, 2026 at 11:20:21AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
> > On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
> > > On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
> > > > This allows to build the kernel with CONFIG_VT enabled, and choose
> > > > on the kernel command line to enable it or not.
> > >
> > > This says what is happening, but not why?
> > >
> > > > Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
> > >
> > > Why are we using a 1990's technology for a new feature? What is this
> > > going to allow to have happen? Who needs/wants this? Who will use it?
> > > For what?
> >
> > The goal is to ease the transition to disable CONFIG_VT.
> >
> > So if this is merged, you can boot without VT on any Linux distribution,
> > without rebuilding the kernel.
>
> But that's a distro-specific thing, the distro should be enabling or
> disabling the option as it needs, it should not be a user-configurable
> boot-time selection option as userspace depends entirely on this either
> being there or not. Why would you have a kernel with both options but
> userspace without that?
And to follow-up on this, if a distro wanted to support this, why not
just provide 2 different kernel images? One with this enabled and one
without? It's up to the distro to support such a thing, not the kernel
community, right?
thanks,
greg k-h
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Jocelyn Falempe @ 2026-01-26 10:48 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <2026012648-vantage-mummified-2a43@gregkh>
On 26/01/2026 11:20, Greg Kroah-Hartman wrote:
> On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
>> On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
>>> On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
>>>> This allows to build the kernel with CONFIG_VT enabled, and choose
>>>> on the kernel command line to enable it or not.
>>>
>>> This says what is happening, but not why?
>>>
>>>> Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
>>>
>>> Why are we using a 1990's technology for a new feature? What is this
>>> going to allow to have happen? Who needs/wants this? Who will use it?
>>> For what?
>>
>> The goal is to ease the transition to disable CONFIG_VT.
>>
>> So if this is merged, you can boot without VT on any Linux distribution,
>> without rebuilding the kernel.
>
> But that's a distro-specific thing, the distro should be enabling or
> disabling the option as it needs, it should not be a user-configurable
> boot-time selection option as userspace depends entirely on this either
> being there or not. Why would you have a kernel with both options but
> userspace without that?
Actually the userspace side works with or without VT, at least with
Fedora, I've my Gnome session in both cases.
>
>> This option will also allow a distribution to disable VT by default, but
>> users that really wants this can enable it on the kernel command line,
>> without rebuilding the kernel.
>
> Why would a user want that? If a user really wants it enabled, why
> would userspace even still work and why would they want to not rebuild
> the kernel?
Rebuilding kernel is not user-friendly, changing a kernel cmdline
parameter is much easier.
>
>> It will also avoid hacky solution in userspace like this:
>> https://overhead.neocities.org/blog/systemd-logind-seat/#very-hacky-solutions
>
> Surely that can't be the only way, why can't userspace just handle this
> "properly" if it wants to?
There is no way for userspace to disable the tty that are running in the
kernel. It can at best ignore them, but for me it's not a proper solution.
>
>>>> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
>>>> ---
>>>> drivers/tty/Kconfig | 13 +++++++++++++
>>>> drivers/tty/vt/vt.c | 5 +++++
>>>> 2 files changed, 18 insertions(+)
>>>>
>>>> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
>>>> index 149f3d53b7608..2b94c2710687a 100644
>>>> --- a/drivers/tty/Kconfig
>>>> +++ b/drivers/tty/Kconfig
>>>> @@ -41,6 +41,19 @@ config VT
>>>> If unsure, say Y, or else you won't be able to do much with your new
>>>> shiny Linux system :-)
>>>> +config VT_ENABLE
>>>> + depends on VT
>>>> + default y
>>>> + bool "enable VT terminal" if EXPERT
>>>
>>> So no one will ever really use this config option?
>>>
>>> And you are doing 2 things in this patch, not just one, unlike what the
>>> changelog said :(
>>
>> I can split that in two if you prefer.
>
> I'm objecting to the patch doing something other than what the changelog
> describes, which as you know is not a good thing.
>
ok, I can fix that in a v2.
>> Adding a module parameter, and adding a Kconfig option, to choose the
>> default for this module parameter.
>
> I really don't like adding new module parameters that we are going to
> have to now support for forever. Why not just rely on the config option
> being there or not as-is? That's why we allowed it to be turned off at
> all, because userspace was going to be moved to not need it anymore.
> Why would we want to support "both" at the same time in the kernel?
>
This parameter is there to ease the transition to VT-less system. So by
maintaining this few lines of code, it will be possible to deprecate the
whole VT in the future.
If a module parameter is not a good solution, I'm open to any solution
that can disable vt from the kernel command line (userspace init runs to
late to disable vt).
> thanks,
>
> greg k-h
>
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Jocelyn Falempe @ 2026-01-26 10:49 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <2026012659-credit-suing-72ce@gregkh>
On 26/01/2026 11:30, Greg Kroah-Hartman wrote:
> On Mon, Jan 26, 2026 at 11:20:21AM +0100, Greg Kroah-Hartman wrote:
>> On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
>>> On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
>>>> On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
>>>>> This allows to build the kernel with CONFIG_VT enabled, and choose
>>>>> on the kernel command line to enable it or not.
>>>>
>>>> This says what is happening, but not why?
>>>>
>>>>> Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
>>>>
>>>> Why are we using a 1990's technology for a new feature? What is this
>>>> going to allow to have happen? Who needs/wants this? Who will use it?
>>>> For what?
>>>
>>> The goal is to ease the transition to disable CONFIG_VT.
>>>
>>> So if this is merged, you can boot without VT on any Linux distribution,
>>> without rebuilding the kernel.
>>
>> But that's a distro-specific thing, the distro should be enabling or
>> disabling the option as it needs, it should not be a user-configurable
>> boot-time selection option as userspace depends entirely on this either
>> being there or not. Why would you have a kernel with both options but
>> userspace without that?
>
> And to follow-up on this, if a distro wanted to support this, why not
> just provide 2 different kernel images? One with this enabled and one
> without? It's up to the distro to support such a thing, not the kernel
> community, right?
That's clearly not an option, they will prefer to keep VT enabled
forever than adding yet another kernel package. And for distributions
that already have kernel and kernel-rt, that means maintaining 4 kernels
for all combination.
>
> thanks,
>
> greg k-h
>
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Greg Kroah-Hartman @ 2026-01-26 10:57 UTC (permalink / raw)
To: Jocelyn Falempe
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <40fa8cab-af36-4420-9099-511474833fe1@redhat.com>
On Mon, Jan 26, 2026 at 11:49:45AM +0100, Jocelyn Falempe wrote:
> On 26/01/2026 11:30, Greg Kroah-Hartman wrote:
> > On Mon, Jan 26, 2026 at 11:20:21AM +0100, Greg Kroah-Hartman wrote:
> > > On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
> > > > On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
> > > > > On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
> > > > > > This allows to build the kernel with CONFIG_VT enabled, and choose
> > > > > > on the kernel command line to enable it or not.
> > > > >
> > > > > This says what is happening, but not why?
> > > > >
> > > > > > Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
> > > > >
> > > > > Why are we using a 1990's technology for a new feature? What is this
> > > > > going to allow to have happen? Who needs/wants this? Who will use it?
> > > > > For what?
> > > >
> > > > The goal is to ease the transition to disable CONFIG_VT.
> > > >
> > > > So if this is merged, you can boot without VT on any Linux distribution,
> > > > without rebuilding the kernel.
> > >
> > > But that's a distro-specific thing, the distro should be enabling or
> > > disabling the option as it needs, it should not be a user-configurable
> > > boot-time selection option as userspace depends entirely on this either
> > > being there or not. Why would you have a kernel with both options but
> > > userspace without that?
> >
> > And to follow-up on this, if a distro wanted to support this, why not
> > just provide 2 different kernel images? One with this enabled and one
> > without? It's up to the distro to support such a thing, not the kernel
> > community, right?
>
> That's clearly not an option, they will prefer to keep VT enabled forever
> than adding yet another kernel package.
But that's a distro's choice to make, why are you forcing this onto the
kernel? Either a distro wants to support a userspace with VT enabled,
or not. So then choose the kernel option you wish to have here and away
you go!
> And for distributions that already have kernel and kernel-rt, that
> means maintaining 4 kernels for all combination.
Again, that's a distro choice, you are now forcing us to maintain the
option due to the lack of an agreement in your organization :)
thanks,
greg k-h
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Greg Kroah-Hartman @ 2026-01-26 10:59 UTC (permalink / raw)
To: Jocelyn Falempe
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <45526d98-57b6-456e-babc-61b7331318c0@redhat.com>
On Mon, Jan 26, 2026 at 11:48:50AM +0100, Jocelyn Falempe wrote:
> On 26/01/2026 11:20, Greg Kroah-Hartman wrote:
> > On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
> > > On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
> > > > On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
> > > > > This allows to build the kernel with CONFIG_VT enabled, and choose
> > > > > on the kernel command line to enable it or not.
> > > >
> > > > This says what is happening, but not why?
> > > >
> > > > > Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
> > > >
> > > > Why are we using a 1990's technology for a new feature? What is this
> > > > going to allow to have happen? Who needs/wants this? Who will use it?
> > > > For what?
> > >
> > > The goal is to ease the transition to disable CONFIG_VT.
> > >
> > > So if this is merged, you can boot without VT on any Linux distribution,
> > > without rebuilding the kernel.
> >
> > But that's a distro-specific thing, the distro should be enabling or
> > disabling the option as it needs, it should not be a user-configurable
> > boot-time selection option as userspace depends entirely on this either
> > being there or not. Why would you have a kernel with both options but
> > userspace without that?
>
> Actually the userspace side works with or without VT, at least with Fedora,
> I've my Gnome session in both cases.
Great! Then why is this even needed? Who wants such a "let's not make
up our mind until we boot" type of system?
Given that traditionally the command line is a "secure" thing, that is
locked down by distros and orginizations, who would ever be able to be
changing this type of thing? Who would want to support userspace that
handles both at the same time?
I don't see the issue here, if a distro doesn't want to support VT, then
disable it in the kernel and all is good. If they do want to support
it, than enable it. Don't do both :)
thanks,
greg k-h
^ permalink raw reply
* Re: [PATCH] vt: Add enable module parameter
From: Jocelyn Falempe @ 2026-01-26 12:26 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, Nicolas Pitre, Calixte Pernot, linux-kernel,
linux-serial
In-Reply-To: <2026012642-threefold-atypical-a3ad@gregkh>
On 26/01/2026 11:59, Greg Kroah-Hartman wrote:
> On Mon, Jan 26, 2026 at 11:48:50AM +0100, Jocelyn Falempe wrote:
>> On 26/01/2026 11:20, Greg Kroah-Hartman wrote:
>>> On Mon, Jan 26, 2026 at 10:43:35AM +0100, Jocelyn Falempe wrote:
>>>> On 26/01/2026 10:33, Greg Kroah-Hartman wrote:
>>>>> On Mon, Jan 26, 2026 at 10:21:50AM +0100, Jocelyn Falempe wrote:
>>>>>> This allows to build the kernel with CONFIG_VT enabled, and choose
>>>>>> on the kernel command line to enable it or not.
>>>>>
>>>>> This says what is happening, but not why?
>>>>>
>>>>>> Add vt.enable=1 to force enable, or vt.enable=0 to force disable.
>>>>>
>>>>> Why are we using a 1990's technology for a new feature? What is this
>>>>> going to allow to have happen? Who needs/wants this? Who will use it?
>>>>> For what?
>>>>
>>>> The goal is to ease the transition to disable CONFIG_VT.
>>>>
>>>> So if this is merged, you can boot without VT on any Linux distribution,
>>>> without rebuilding the kernel.
>>>
>>> But that's a distro-specific thing, the distro should be enabling or
>>> disabling the option as it needs, it should not be a user-configurable
>>> boot-time selection option as userspace depends entirely on this either
>>> being there or not. Why would you have a kernel with both options but
>>> userspace without that?
>>
>> Actually the userspace side works with or without VT, at least with Fedora,
>> I've my Gnome session in both cases.
>
> Great! Then why is this even needed? Who wants such a "let's not make
> up our mind until we boot" type of system?
>
> Given that traditionally the command line is a "secure" thing, that is
> locked down by distros and orginizations, who would ever be able to be
> changing this type of thing? Who would want to support userspace that
> handles both at the same time?
>
> I don't see the issue here, if a distro doesn't want to support VT, then
> disable it in the kernel and all is good. If they do want to support
> it, than enable it. Don't do both :)
Maybe the real issue is that VT cannot be built as a module.
That way the userspace would be able to load it only if it needs it.
That's probably more complex than my 3 lines patch, but I can try.
Would you prefer it that way?
>
> thanks,
>
> greg k-h
>
^ permalink raw reply
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