serial: qcom_geni: Add panic notifier to stop UART on panic

When a VM crashes with an active UART DMA transfer in progress, the
SMMU raises context faults as the DMA engine continues to access IOVAs
that are invalidated when the VM's memory context is torn down. These
faults can affect other VMs sharing the same SMMU instance and obscure
the root cause of the crash. Additionally, a stuck TX transfer on the
panic console UART can cause the panic handler to stall, dropping the
panic output.

Register a panic notifier to stop TX and RX. The notifier does not take
the port lock, since panic can be entered with the lock already held by
the interrupted context, and there is no safe way to detect that here;
instead, the device's runtime PM status is checked first so that TX/RX
are only stopped while the hardware is still clocked and accessible,
and the register accesses are skipped entirely once the device is
runtime suspended.

Signed-off-by: Praveen Talari <praveen.talari@oss.qualcomm.com>
Link: https://patch.msgid.link/20260715-add_shutdown_and_panic_notifier_serial-v1-2-23e3787c7109@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 04e1227390dd..67b14fda4ff9 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -18,6 +18,7 @@
 #include <linux/irq.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/panic_notifier.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_opp.h>
 #include <linux/platform_device.h>
@@ -156,6 +157,7 @@ struct qcom_geni_serial_port {
 	struct qcom_geni_private_data private_data;
 	const struct qcom_geni_device_data *dev_data;
 	struct dev_pm_domain_list *pd_list;
+	struct notifier_block panic_nb;
 };
 
 static const struct uart_ops qcom_geni_console_pops;
@@ -1824,6 +1826,22 @@ static const struct uart_ops qcom_geni_uart_pops = {
 	.pm = qcom_geni_serial_pm,
 };
 
+static int qcom_geni_serial_panic_notifier(struct notifier_block *nb,
+					   unsigned long action, void *data)
+{
+	struct qcom_geni_serial_port *port =
+		container_of(nb, struct qcom_geni_serial_port, panic_nb);
+	struct uart_port *uport = &port->uport;
+
+	if (pm_runtime_status_suspended(uport->dev))
+		return NOTIFY_OK;
+
+	qcom_geni_serial_stop_tx(uport);
+	qcom_geni_serial_stop_rx(uport);
+
+	return NOTIFY_OK;
+}
+
 static int qcom_geni_serial_probe(struct platform_device *pdev)
 {
 	int ret = 0;
@@ -1959,6 +1977,9 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
 	if (ret)
 		goto error;
 
+	port->panic_nb.notifier_call = qcom_geni_serial_panic_notifier;
+	atomic_notifier_chain_register(&panic_notifier_list, &port->panic_nb);
+
 	return 0;
 
 error:
@@ -1977,6 +1998,8 @@ static void qcom_geni_serial_remove(struct platform_device *pdev)
 	struct uart_port *uport = &port->uport;
 	struct uart_driver *drv = port->private_data.drv;
 
+	atomic_notifier_chain_unregister(&panic_notifier_list, &port->panic_nb);
+
 	dev_pm_clear_wake_irq(&pdev->dev);
 	device_init_wakeup(&pdev->dev, false);
 	ida_free(&port_ida, uport->line);