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

[Michael Walle]

Am 2022-11-22 09:25, schrieb Jiri Slaby:
> On 22. 11. 22, 9:23, Jiri Slaby wrote:
> > On 22. 11. 22, 9:18, Michael Walle wrote:
> > > 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?
> >
> > Yes, that was exactly the next step to try. The datasheet doesn't tell 
> > much what happens when TXDIS is written while the characters are 
> > transmitted.
>
> Side note: your usart doesn't use dma. It's PIO (hence all that
> uart_tx_helper()). And the attached patch doesn't touch TXDIS for
> non-DMA case. I.e. it should transmit the final character (and nothing
> more).

ok ;)

expect from "s/id_dma/is_dma/", this patch works. thanks!

-michael