imx: RS-485 problems during TX, maybe DMA related
From: festevam@gmail.com (Fabio Estevam)
Date: 2017-01-08 21:46:57
Also in:
linux-serial, lkml
On Sun, Jan 8, 2017 at 4:06 PM, Clemens Gruber [off-list ref] wrote:
I just did the experiment with your configuration and the rs485conf tool you mentioned. But still, no luck :( What's the revision of the i.MX6Q on your board? Mine is 1.5 (TO 1.3)
Mine is a mx6solo rev1.1.
Another example: If I run the following on the board.. while true; do echo ABCDEFGHIJKLM > /dev/ttymxc4 sleep 0.5 echo abc > /dev/ttymxc4 > /dev/ttymxc4
There is a typo here, this should be: echo abc > /dev/ttymxc4 Fixed it locally.
sleep 0.5 done Many transmits contain garbled (doubled and sometimes also extended to a length of 4096 bytes, containing zeros) data. I can see a few transmissions that are sent correctly, though.
This script runs correctly here and no issue is seen on the console. Not sure why you get TXEN high for so long in your case.
quoted hunk ↗ jump to hunk
Interesting side note: With the following patch, the problems disappear:diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 451e50f6d77a..eb9f0ce6c34a 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c@@ -1270,8 +1270,10 @@ static int imx_startup(struct uart_port *port) writel(temp & ~UCR4_DREN, sport->port.membase + UCR4); /* Can we enable the DMA support? */ +#if 0 if (!uart_console(port) && !sport->dma_is_inited) imx_uart_dma_init(sport); +#endif
Looks like you disabled DMA. Regards, Fabio Estevam