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

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