FAILED: patch "[PATCH] serial: qcom-geni: fix TX DMA buffer flush" failed to apply to 6.6-stable tree

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

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2026-08-17 12:24 UTC #0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

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

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x e3c04834ae1ab5e9cfbe8ac54ec734aa4774249d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026081743-aghast-resisting-a8ca@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From e3c04834ae1ab5e9cfbe8ac54ec734aa4774249d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Sebastian=20G=C3=B6tte?= <[email protected]>
Date: Wed, 29 Jul 2026 19:41:05 +0200
Subject: [PATCH] serial: qcom-geni: fix TX DMA buffer flush
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When transmit flushing a qcom-geni UART during an ongoing TX DMA, the UART gets stuck infinitely repeating corrupted TX DMA frames.

The DMA-mode uart_ops does not provide a flush_buffer callback, so an in-flight transfer can complete after serial core has reset the transmit kfifo, underflowing its length and resubmitting page-sized transfers indefinitely. Add one that stops the transfer and clears tx_remaining and tx_queued.

The stop path was also broken: it unmapped the buffer while the serial engine could still read it, and never reset the TX DMA state machine. Cancel the main sequencer command first, then reset the state machine and wait for it before unmapping. Drop the early return so a pending mapping is also cleaned up when the main command is inactive.

The bug can be triggered from userspace with a large write immediately followed by TCOFLUSH. A following tcdrain will hang forever. The bug was reproduced and this fix was validated on Arduino Uno Q (QRB2210) using /dev/ttyHS1.

Assisted-by Claude:claude-5-opus Codex:gpt-5

Signed-off-by Jan Sebastian Götte <[email protected]>

Fixes 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")

Cc stable <[email protected]>

Reviewed-by Praveen Talari <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Greg Kroah-Hartman <[email protected]>

drivers/tty/serial/qcom_geni_serial.c +22 ~~-21~~

index 7ead87b4eb65..1e39122ec09f 100644
@@ -158,6 +158,7 @@ static const struct uart_ops qcom_geni_uart_pops;
 static struct uart_driver qcom_geni_console_driver;
 static struct uart_driver qcom_geni_uart_driver;
 
+static void qcom_geni_serial_stop_tx_dma(struct uart_port *uport);
 static void __qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport);
 static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport);
 static int qcom_geni_serial_port_setup(struct uart_port *uport);

@@ -636,35 +637,34 @@ static unsigned int qcom_geni_serial_tx_empty(struct uart_port *uport)
 	return !readl(uport->membase + SE_GENI_TX_FIFO_STATUS);
 }
 
+static void qcom_geni_serial_flush_buffer_dma(struct uart_port *uport)
+{
+	struct qcom_geni_serial_port *port = to_dev_port(uport);
+
+	qcom_geni_serial_stop_tx_dma(uport);
+	port->tx_remaining = 0;
+	port->tx_queued = 0;
+}
+
 static void qcom_geni_serial_stop_tx_dma(struct uart_port *uport)
 {
 	struct qcom_geni_serial_port *port = to_dev_port(uport);
-	bool done;
 
-	if (!qcom_geni_serial_main_active(uport))
-		return;
+	if (qcom_geni_serial_main_active(uport))
+		__qcom_geni_serial_cancel_tx_cmd(uport);
 
 	if (port->tx_dma_addr) {
+		writel(1, uport->membase + SE_DMA_TX_FSM_RST);
+		if (!qcom_geni_serial_poll_bit(uport, SE_DMA_TX_IRQ_STAT,
+					       TX_RESET_DONE, true))
+			dev_err_ratelimited(uport->dev, "TX DMA reset failed");
+		writel(TX_RESET_DONE | TX_DMA_DONE,
+		       uport->membase + SE_DMA_TX_IRQ_CLR);
+
 		geni_se_tx_dma_unprep(&port->se, port->tx_dma_addr,
 				      port->tx_remaining);
 		port->tx_dma_addr = 0;
-		port->tx_remaining = 0;
 	}
-
-	geni_se_cancel_m_cmd(&port->se);
-
-	done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
-					 M_CMD_CANCEL_EN, true);
-	if (!done) {
-		geni_se_abort_m_cmd(&port->se);
-		done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
-						 M_CMD_ABORT_EN, true);
-		if (!done)
-			dev_err_ratelimited(uport->dev, "M_CMD_ABORT_EN not set");
-		writel(M_CMD_ABORT_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
-	}
-
-	writel(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 }
 
 static void qcom_geni_serial_start_tx_dma(struct uart_port *uport)

@@ -1180,7 +1180,7 @@ static void qcom_geni_serial_shutdown(struct uart_port *uport)
 	uart_port_unlock_irq(uport);
 }
 
-static void qcom_geni_serial_flush_buffer(struct uart_port *uport)
+static void qcom_geni_serial_flush_buffer_fifo(struct uart_port *uport)
 {
 	qcom_geni_serial_cancel_tx_cmd(uport);
 }

@@ -1769,7 +1769,7 @@ static const struct uart_ops qcom_geni_console_pops = {
 	.request_port = qcom_geni_serial_request_port,
 	.config_port = qcom_geni_serial_config_port,
 	.shutdown = qcom_geni_serial_shutdown,
-	.flush_buffer = qcom_geni_serial_flush_buffer,
+	.flush_buffer = qcom_geni_serial_flush_buffer_fifo,
 	.type = qcom_geni_serial_get_type,
 	.set_mctrl = qcom_geni_serial_set_mctrl,
 	.get_mctrl = qcom_geni_serial_get_mctrl,

@@ -1792,6 +1792,7 @@ static const struct uart_ops qcom_geni_uart_pops = {
 	.request_port = qcom_geni_serial_request_port,
 	.config_port = qcom_geni_serial_config_port,
 	.shutdown = qcom_geni_serial_shutdown,
+	.flush_buffer = qcom_geni_serial_flush_buffer_dma,
 	.type = qcom_geni_serial_get_type,
 	.set_mctrl = qcom_geni_serial_set_mctrl,
 	.get_mctrl = qcom_geni_serial_get_mctrl,

Sasha Levin

maintainer

2026-08-21 04:00 UTC #1 lore raw

PATCH 1/1 serial: qcom-geni: fix TX DMA buffer flush

From: Jan Sebastian Götte <[email protected]>

[ Upstream commit e3c04834ae1ab5e9cfbe8ac54ec734aa4774249d ]

When transmit flushing a qcom-geni UART during an ongoing TX DMA, the UART gets stuck infinitely repeating corrupted TX DMA frames.

Assisted-by Claude:claude-5-opus Codex:gpt-5

Signed-off-by Jan Sebastian Götte <[email protected]>

Fixes 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")

Cc stable <[email protected]>

Reviewed-by Praveen Talari <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Greg Kroah-Hartman <[email protected]>

[ Inlined `__qcom_geni_serial_cancel_tx_cmd()` as the existing open-coded cancel/abort block and dropped the `flush_buffer`→`flush_buffer_fifo` rename and `tx_queued` reset, which don't exist in this tree. ]

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/tty/serial/qcom_geni_serial.c | 51 +++++++++++++++++----------
 1 file changed, 33 insertions(+), 18 deletions(-)

drivers/tty/serial/qcom_geni_serial.c +33 ~~-18~~

index ab5b4c6c29de0..91c502e833e16 100644
@@ -144,6 +144,7 @@ static const struct uart_ops qcom_geni_uart_pops;
 static struct uart_driver qcom_geni_console_driver;
 static struct uart_driver qcom_geni_uart_driver;
 
+static void qcom_geni_serial_stop_tx_dma(struct uart_port *uport);
 static int qcom_geni_serial_port_setup(struct uart_port *uport);
 
 static inline struct qcom_geni_serial_port *to_dev_port(struct uart_port *uport)

@@ -597,35 +598,48 @@ static unsigned int qcom_geni_serial_tx_empty(struct uart_port *uport)
 	return !readl(uport->membase + SE_GENI_TX_FIFO_STATUS);
 }
 
+static void qcom_geni_serial_flush_buffer_dma(struct uart_port *uport)
+{
+	struct qcom_geni_serial_port *port = to_dev_port(uport);
+
+	qcom_geni_serial_stop_tx_dma(uport);
+	port->tx_remaining = 0;
+}
+
 static void qcom_geni_serial_stop_tx_dma(struct uart_port *uport)
 {
 	struct qcom_geni_serial_port *port = to_dev_port(uport);
 	bool done;
 
-	if (!qcom_geni_serial_main_active(uport))
-		return;
+	if (qcom_geni_serial_main_active(uport)) {
+		geni_se_cancel_m_cmd(&port->se);
+
+		done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
+						 M_CMD_CANCEL_EN, true);
+		if (!done) {
+			geni_se_abort_m_cmd(&port->se);
+			done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
+							 M_CMD_ABORT_EN, true);
+			if (!done)
+				dev_err_ratelimited(uport->dev, "M_CMD_ABORT_EN not set");
+			writel(M_CMD_ABORT_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
+		}
+
+		writel(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
+	}
 
 	if (port->tx_dma_addr) {
+		writel(1, uport->membase + SE_DMA_TX_FSM_RST);
+		if (!qcom_geni_serial_poll_bit(uport, SE_DMA_TX_IRQ_STAT,
+					       TX_RESET_DONE, true))
+			dev_err_ratelimited(uport->dev, "TX DMA reset failed");
+		writel(TX_RESET_DONE | TX_DMA_DONE,
+		       uport->membase + SE_DMA_TX_IRQ_CLR);
+
 		geni_se_tx_dma_unprep(&port->se, port->tx_dma_addr,
 				      port->tx_remaining);
 		port->tx_dma_addr = 0;
-		port->tx_remaining = 0;
-	}
-
-	geni_se_cancel_m_cmd(&port->se);
-
-	done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
-					 M_CMD_CANCEL_EN, true);
-	if (!done) {
-		geni_se_abort_m_cmd(&port->se);
-		done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
-						 M_CMD_ABORT_EN, true);
-		if (!done)
-			dev_err_ratelimited(uport->dev, "M_CMD_ABORT_EN not set");
-		writel(M_CMD_ABORT_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 	}
-
-	writel(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 }
 
 static void qcom_geni_serial_start_tx_dma(struct uart_port *uport)

@@ -1600,6 +1614,7 @@ static const struct uart_ops qcom_geni_uart_pops = {
 	.request_port = qcom_geni_serial_request_port,
 	.config_port = qcom_geni_serial_config_port,
 	.shutdown = qcom_geni_serial_shutdown,
+	.flush_buffer = qcom_geni_serial_flush_buffer_dma,
 	.type = qcom_geni_serial_get_type,
 	.set_mctrl = qcom_geni_serial_set_mctrl,
 	.get_mctrl = qcom_geni_serial_get_mctrl,

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