drivers/tty/serial/serial_port.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-)
From: Yicong Yang <yangyicong@hisilicon.com>
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.
Cc: Tony Lindgren <tony@atomide.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
Change since v3:
- Drop non-fix change in __serial_port_busy()
- Use a boolen busy instead of ret per Jiri
Link: https://lore.kernel.org/all/20240208075216.48915-1-yangyicong@huawei.com/
Change since v2:
- Narrow the spinlock region per Andy
- Make __serial_port_busy() return -EBUSY if port has pending chars per Andy
Thanks.
Link: https://lore.kernel.org/all/20240206073322.5560-1-yangyicong@huawei.com/
Change since v1:
- Use port lock wrapper per John
- Flush the pending chars and return -EBUSY per Tony.
Thanks.
Link: https://lore.kernel.org/all/20240204031957.58176-1-yangyicong@huawei.com/
drivers/tty/serial/serial_port.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index 88975a4df306..1843c9ef7c49 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -46,8 +46,33 @@ static int serial_port_runtime_resume(struct device *dev)
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;
+ unsigned long flags;
+ bool busy;
+
+ port = port_dev->port;
+
+ 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)
{
--
2.24.0
On Fri, Feb 23, 2024 at 04:39:03PM +0800, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@hisilicon.com>
>
> 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.
...
> Cc: Tony Lindgren <tony@atomide.com>
No need to Cc to people whose tags you already have. The Git tools will add
them to the Cc list.
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Jiri Slaby <jirislaby@kernel.org>
In general, Cc is better to be either supplied with --cc or be located after
the cutter '---' line, so they won't pollute the commit message.
...
Code wise LGTM, thanks.
Minor remarks below, with them addressed,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> +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;
You can assign here
struct uart_port *port = port_dev->port;
and save 2 LoCs.
> + unsigned long flags;
> + bool busy;
> +
> + port = port_dev->port;
> +
If you want to have assignment separated, this blank line may be dropped.
> + 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;
> +}
--
With Best Regards,
Andy Shevchenko
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