Le 15/03/2017 ? 17:19, Richard Genoud a ?crit :

On 15/03/2017 16:29, Nicolas Ferre wrote:

quoted

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@microchip.com>
Fixes: 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA from transmitting
in stop_tx")
Cc: stable <redacted> # 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,

quoted

 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