* Tony Lindgren <tony@xxxxxxxxxxx> [220407 13:25]: > Hi, > > * Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> [700101 02:00]: > > From: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> > > > > Don't start the whole chain for TX if there is no data to send. This is > > mostly relevant for rs485 mode as there might be rts-before-send and > > rts-after-send delays involved. > > > > Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > > --- > > Hello, > > > > a few other drivers have such an early exit already (imx, stm32-usart). > > I wonder if it applies to all UART drivers that there is nothing to do > > in .start_tx() if the circ buffer is empty and there is no x_char to > > send. In this case it would be more sensible to ensure in serial_core > > that .start_tx() is only ever called if there is something to do. > > This patch seems to cause a runtime PM regression in v5.18-rc1 where > 8250 is never idled for omaps. > > Looks like the return added here is not paired with put for the > serial8250_rpm_get_tx() call above? FYI I just posted two fixes for these early return cases: https://lore.kernel.org/linux-serial/20220411094805.45696-1-tony@xxxxxxxxxxx/T/#t Regards, Tony
