Re: [PATCH v3 00/12] Add RS485 support to DW UART

On Sun, 24 Apr 2022, Vicente Bergas wrote:

Hi Ilpo, thank you for your quick reply with a solution!

On Fri, Apr 22, 2022 at 3:07 PM Ilpo Järvinen
[off-list ref] wrote:

quoted

On Fri, 22 Apr 2022, Ilpo Järvinen wrote:

quoted

On Thu, 21 Apr 2022, Vicente Bergas wrote:

quoted

1.- rs485_stop_tx is never called because there are no interrupts.
I worked around this by disabling DMA:

I'll need to look into this.

8250 DMA tx complete path lacks calls to normal 8250 stop handling and
I think it probably also assumes too much from dmaengine's completion
callback. ...It also seems bit early to call serial8250_rpm_put_tx from
there(?).

This patch allowed em485_start/stop_tx to be called in my tests:
[PATCH 1/1] serial: 8250: use THRE & __stop_tx also with DMA

I confirm that this patch fixes the issue when DMA is enabled.

I also confirm that your other patch

quoted

+                       stop_delay = p->port.frame_time + DIV_ROUND_UP(p->port.frame_time, 7);

fixes the issue with RTS/DriverEnable deassertion time.
I've tested it again at 19200e1 and now RTS is deasserted
approximately at the same time as the end of the stop bit.
Please, note the "e" for even parity bit, that extra bit after the
data byte might have an impact on this timings.

Great, thanks again for testing.

I don't think that parity "e" makes the calculations incorrect as parity 
bit should be taken into account in tty_get_frame_size(). My guess is it's 
more about whether THRE might get asserted already during the stop bit or 
only after the stop bit has been fully sent.


-- 
 i.