linux-kernel - Re: [PATCH v5 2/3] tty: serial: use uart_port

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Date:   Tue, 22 Nov 2022 09:23:11 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     afaerber@...e.de, alexandre.belloni@...tlin.com,
        claudiu.beznea@...rochip.com, festevam@...il.com,
        gregkh@...uxfoundation.org, ilpo.jarvinen@...ux.intel.com,
        kernel@...gutronix.de, linux-imx@....com,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        liviu.dudau@....com, lorenzo.pieralisi@....com, mani@...nel.org,
        nicolas.ferre@...rochip.com, richard.genoud@...il.com,
        s.hauer@...gutronix.de, shawnguo@...nel.org, sudeep.holla@....com,
        tklauser@...tanz.ch, vz@...ia.com
Subject: Re: [PATCH v5 2/3] tty: serial: use uart_port_tx() helper

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. So can you give the attached patch a try?

thanks,
-- 
js

View attachment "0001-atmel-fix.patch" of type "text/x-patch" (2779 bytes)