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? thanks, greg k-h
