linux-kernel - Re: [RFC PATCH] tty/serial: atmel: fix TX path in atmel_console

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Message-ID: <d3abc5aa-b010-a6cc-4ab9-74078149a692@microchip.com>
Date:   Wed, 15 Mar 2017 17:56:11 +0100
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Richard Genoud <richard.genoud@...il.com>,
        <linux-serial@...r.kernel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "stable # 4 . 4+" <stable@...r.kernel.org>
Subject: Re: [RFC PATCH] tty/serial: atmel: fix TX path in
 atmel_console_write()

Le 15/03/2017 à 17:19, Richard Genoud a écrit :
> On 15/03/2017 16:29, Nicolas Ferre wrote:
>> A side effect of 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA
>> from transmitting in stop_tx") is that the console can be called with
>> TX path disabled. Then the system would hang trying to push charecters
>> out in atmel_console_putchar().
>>
>> Signed-off-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
>> Fixes: 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA from transmitting
>> in stop_tx")
>> Cc: stable <stable@...r.kernel.org> # 4.4+
>> ---
>> Hi Richard,
>>
>> I found this to fix the problem with system hang in my linux-4.4-at91 branch
>> (in the atmel_console_putchar() waiting loop actually). I'm open to more
>> insignt.
>> As we cannot figure out if this bit is set or not, I didn't preserve the
>> current status...
>>
>> Regards,
> 
> So, I'm guessing that you may see some lines/characters printed twice on
> the screen, don't you ?

Well, actually, I don't think so because the repetitions that I see are
probably due to open/close/open/close/re-open/... of the serial console
itself.

Same with the line "random: udevd: uninitialized urandom read (16 bytes
read, 21 bits of entropy available)", they happen at different moment in
time => the printk log timestamping seem to indicate that they are
different.

Here is my log:
http://code.bulix.org/bok23n-123056

Regards,

>>  drivers/tty/serial/atmel_serial.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index dcebb28ffbc4..7372dbdb7a4c 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -2483,6 +2483,9 @@ static void atmel_console_write(struct console *co, const char *s, u_int count)
>>  	pdc_tx = atmel_uart_readl(port, ATMEL_PDC_PTSR) & ATMEL_PDC_TXTEN;
>>  	atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
>>  
>> +	/* Make sure that tx path is actually able to send characters */
>> +	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
>> +
>>  	uart_console_write(port, s, count, atmel_console_putchar);
>>  
>>  	/*
>>
> 
> Richard.
> 


-- 
Nicolas Ferre