Messages in this thread | | | Date | Tue, 22 Nov 2022 09:25:36 +0100 | Subject | Re: [PATCH v5 2/3] tty: serial: use uart_port_tx() helper | From | Jiri Slaby <> |
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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).
-- js
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