Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> writes: > On Thu, May 30, 2019 at 06:29:43PM +0300, Sergey Organov wrote: >> imx_set_mctrl() had TIOCM_DTR meaning inverted >> >> Signed-off-by: Sergey Organov <sorganov@xxxxxxxxx> >> --- >> drivers/tty/serial/imx.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c >> index dff75dc..e9e812a 100644 >> --- a/drivers/tty/serial/imx.c >> +++ b/drivers/tty/serial/imx.c >> @@ -974,7 +974,7 @@ static void imx_uart_set_mctrl(struct uart_port *port, unsigned int mctrl) >> } >> >> ucr3 = imx_uart_readl(sport, UCR3) & ~UCR3_DSR; >> - if (!(mctrl & TIOCM_DTR)) >> + if (mctrl & TIOCM_DTR) >> ucr3 |= UCR3_DSR; >> imx_uart_writel(sport, ucr3, UCR3); > > I'm not sure this is right and your commit log is too short to convince > me otherwise. > > In the past I had several customers that used handshaking on an imx UART > so I'd be surprised if such a bug would have stayed unnoticed until now. > > The i.MX25 Reference manual states: > > This bit [UCR3_DSR] used by software to control the DSR/DTR output pin > for the modem interface. In DCE mode it applies to DSR and in DTE mode > it applies to DTR. > > 0 DSR/ DTR pin is logic zero > 1 DSR/ DTR pin is logic one > > > Semantically if TIOCM_DTR is set in .set_mctrl, the DTR output should > become active (i.e. low). Without testing I'm not sure if "active" > corresponds to "logic one" which would make your patch correct. Yeah, I was not sure myself, and this pin is not wired on my board, so in fact I can't check either. Unfortunately, the language in the manual is inconsistent. For CTS/ RTS is clearly says: 0 The CTS_B pin is high (inactive) 1 The CTS_B pin is low (active) and the code in the driver is: if (mctrl & TIOCM_RTS) ucr2 |= UCR2_CTS; that works correct. My best reasoning was that DSR/ DTR is likely implemented the same as CTS/ RTS in the metal, and I found other drivers where both RTS and DSR are inverted, so I guessed it could be a remnant of old copy-paste. -- Sergey
