Re: Opening already open serial port now sets RTS and DTR?

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2022-02-17, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Thu, Feb 17, 2022 at 03:28:00PM -0000, Grant Edwards wrote:
>> It used to be that opening a serial port only set RTS and DTR if it
>> was a "first open". [...]

>> This seems to have changed, and now _every_ open sets RTS and DTR
>> even if the port was already open and RTS and DTR had already been
>> put in the desired state.
>
> When did it change?

I'm not sure. It's been a couple years since the last time I
personally used something that relied on the "old" behavior.

> Any chance you can do 'git bisect' to track it down?

Unfortunately, it would take a lot of work to get set up to do that.

I can probably try the past half-dozen or so Ubuntu distros (I'm not
sure how far back I can go with available hardware). I'll check around
with colleagues to see if we have any existing installations that are
using on the old behavior.

> And what hardware are you using here?

I've tried a couple different FTDI USB devices (FT232R single port and
FT4232H quad port). I've also tried a 16550A motherboard UART. I
believe that both FTDI and 16550 used to set RTS/DTR only on "first
open".

> Different hardware works differently in this way at times.

Which is the "expected correct" behavior?

--
Grant