On 2024/2/6 17:44, Greg KH wrote:
> On Tue, Feb 06, 2024 at 03:33:22PM +0800, Yicong Yang wrote:
>> From: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxx>
>> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
>
> Is this a regression that was caused by the port code? If so, what
> commit id does this fix? Should it be backported to older kernels?
>
Sorry for missing it. The fix tag should be:
Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")
Thanks.
