On 2022-02-17, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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
