6.6-stable review patch. If anyone has any objections, please let me know.
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From: Yicong Yang yangyicong@hisilicon.com
commit 43066e32227ecde674e8ae1fcdd4a1ede67680c2 upstream.
We accidently met the issue that the bash prompt is not shown after the previous command done and until the next input if there's only one CPU (In our issue other CPUs are isolated by isolcpus=). Further analysis shows it's because the port entering runtime suspend even if there's still pending chars in the buffer and the pending chars will only be processed in next device resuming. We are using amba-pl011 and the problematic flow is like below:
Bash kworker tty_write() file_tty_write() n_tty_write() uart_write() __uart_start() pm_runtime_get() // wakeup waker queue_work() pm_runtime_work() rpm_resume() status = RPM_RESUMING serial_port_runtime_resume() port->ops->start_tx() pl011_tx_chars() uart_write_wakeup() […] __uart_start() pm_runtime_get() < 0 // because runtime status = RPM_RESUMING // later data are not commit to the port driver status = RPM_ACTIVE rpm_idle() -> rpm_suspend()
This patch tries to fix this by checking the port busy before entering runtime suspending. A runtime_suspend callback is added for the port driver. When entering runtime suspend the callback is invoked, if there's still pending chars in the buffer then flush the buffer.
Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM") Cc: stable stable@kernel.org Reviewed-by: Tony Lindgren tony@atomide.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Yicong Yang yangyicong@hisilicon.com Link: https://lore.kernel.org/r/20240226152351.40924-1-yangyicong@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/serial_port.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/serial_port.c +++ b/drivers/tty/serial/serial_port.c @@ -46,8 +46,31 @@ out: return 0; }
+static int serial_port_runtime_suspend(struct device *dev) +{ + struct serial_port_device *port_dev = to_serial_base_port_device(dev); + struct uart_port *port = port_dev->port; + unsigned long flags; + bool busy; + + if (port->flags & UPF_DEAD) + return 0; + + uart_port_lock_irqsave(port, &flags); + busy = __serial_port_busy(port); + if (busy) + port->ops->start_tx(port); + uart_port_unlock_irqrestore(port, flags); + + if (busy) + pm_runtime_mark_last_busy(dev); + + return busy ? -EBUSY : 0; +} + static DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm, - NULL, serial_port_runtime_resume, NULL); + serial_port_runtime_suspend, + serial_port_runtime_resume, NULL);
static int serial_port_probe(struct device *dev) {