Re: [PATCH v5 2/3] tty: serial: use uart_port_tx() helper

[Michael Walle]

Am 2022-11-22 09:09, schrieb Michael Walle:
> Hi,
>
> Am 2022-11-22 08:02, schrieb Jiri Slaby:
> > On 21. 11. 22, 21:27, Michael Walle wrote:
> > > This will break serial output for the userspace on my board
> > > (arch/arm/boot/dts/lan966x-kontron-kswitch-d10-mmt*dts). The 
> > > uart_port_tx()
> > > helper will call __port->ops->stop_tx(__port) if 
> > > uart_circ_chars_pending()
> > > returns 0. But the code above, doesn't do that. In fact, removing the
> > > stop_tx() call in the helper macro, will fix the console output.
> > >
> > > Any ideas how to fix that?
> >
> > Hm, so ATMEL_US_TXRDY is removed from tx_done_mask in stop_tx, but not
> > added back in start_tx. So the tx interrupt is never handled (the tx
> > tasklet is not scheduled to send the queue chars) in
> > atmel_handle_transmit().
> >
> > Any chance, the below fixes it?
> >
> > diff --git a/drivers/tty/serial/atmel_serial.c
> > b/drivers/tty/serial/atmel_serial.c
> > index 11bf2466390e..395370e0c77b 100644
> > --- a/drivers/tty/serial/atmel_serial.c
> > +++ b/drivers/tty/serial/atmel_serial.c
> > @@ -596,6 +596,8 @@ static void atmel_start_tx(struct uart_port *port)
> >                 /* re-enable PDC transmit */
> >                 atmel_uart_writel(port, ATMEL_PDC_PTCR, 
> > ATMEL_PDC_TXTEN);
> >
> > +       atmel_port->tx_done_mask |= ATMEL_US_TXRDY;
> > +
> >         /* Enable interrupts */
> >         atmel_uart_writel(port, ATMEL_US_IER, 
> > atmel_port->tx_done_mask);
> >
> >
> > thanks,
>
> Unfortunately, that doesn't help. Btw, some characters are transmitted:
>
>
> [    6.219356] Key type dns_resolver registered
> [    6.223679] Registering SWP/SWPB emulation handler
> [    6.247530] Loading compiled-in X.509 certificates
> [    6.288467] Freeing unused kernel image (initmem) memory: 1024K
> [    6.297789] Run /init as init process
> WbSOROSOSOSOSOStarting linuxptp system clock synchronization: O
>
> -michael

But you made me look at atmel_stop_tx() and there is this:

       /*
	* Disable the transmitter.
	* This is mandatory when DMA is used, otherwise the DMA buffer
	* is fully transmitted.
	*/
	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);

Removing that write, will also fix the problem. Could it be, that
the transmit is still active (via DMA) but the driver will call
tx_stop() and then stop the transmission in the background?

-michael