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Message-ID: <ffb1f40b-bbe8-5431-63cf-a53fc0606971@gmail.com>
Date:   Wed, 23 Nov 2022 13:46:17 +0100
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Subject: Re: [PATCH 2/2] serial: atmel: don't stop the transmitter when doing
 PIO
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To:     Michael Walle <michael@walle.cc>,
        "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc:     gregkh@linuxfoundation.org, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Claudiu Beznea <claudiu.beznea@microchip.com>,
        linux-arm-kernel@lists.infradead.org
References: <20221123082736.24566-1-jirislaby@kernel.org>
 <20221123082736.24566-2-jirislaby@kernel.org>
 <df233ce37626fdb194b583808326d966@walle.cc>
From:   Richard Genoud <richard.genoud@gmail.com>
In-Reply-To: <df233ce37626fdb194b583808326d966@walle.cc>
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Le 23/11/2022 à 09:50, Michael Walle a écrit :
> Am 2022-11-23 09:27, schrieb Jiri Slaby (SUSE):
>> Writing ATMEL_US_TXDIS to ATMEL_US_CR makes the transmitter NOT to send
>> the just queued character. This means when the character is last and
>> uart calls ops->stop_tx(), the character is not sent at all.
>>
>> The usart datasheet is not much specific on this, it just says the
>> transmitter is stopped. But apparently, the character is dropped. So
>> we should stop the transmitter only for DMA and PDC transfers to not
>> send any more characters. For PIO, this is unexpected and deviates from
>> other drivers. In particular, the below referenced commit broke TX as it
>> added a call to ->stop_tx() after the very last character written to the
>> transmitter.
>>
>> So fix this by limiting the write of ATMEL_US_TXDIS to DMA transfers
>> only.
>>
>> Even there, I don't know if it is correctly implemented. Are all the
>> queued characters sent once ->start_tx() is called? Anyone tested flow
>> control -- be it hard (RTSCTS) or the soft (XOFF/XON) one?
>>
>> Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper")
>> Cc: Richard Genoud <richard.genoud@gmail.com>
>> Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
>> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
>> Cc: Claudiu Beznea <claudiu.beznea@microchip.com>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Reported-by: Michael Walle <michael@walle.cc>
>> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
> 
> Already merged, but:
> Tested-by: Michael Walle <michael@walle.cc>
Acked-by: Richard Genoud <richard.genoud@gmail.com>

> 
> Thanks,
> -michael
Thanks !