Hi,

On 07/09/2016 at 18:13:24 +0200, Richard Genoud wrote :

Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
hardware handshake is enabled") broke the hardware handshake when
DMA is not used.

So, here's a summary:
If DMA is NOT USED the mode should be ATMEL_US_USMODE_NORMAL because the
controller can't drive the RTS pin (there's no way for it to know when
we can't receive data anymore).

You forgot that the PDC can properly drive the RTS pin so all the
platforms that are using the PDC will break after your patch.

Also, I believe the controller is able to drive the RTS and CTS pins
when simply using PIOs (it knows when one complete character has been
received and US_RHR has not yet been read). However, I didn't test.
Maybe someone at Atmel can confirm.

I think that 5be605ac9af9 is doing the right thing but I still can be
convince otherwise ;).

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com