linux-kernel - RE: [PATCH V2 2/5] tty: serial: fsl_lpuart: clear UARTCTRL_LOOPS in lpuart32

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Date:   Wed, 23 Nov 2022 10:58:34 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Michael Walle <michael@...le.cc>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "jingchang.lu@...escale.com" <jingchang.lu@...escale.com>,
        "tomonori.sakita@...d.co.jp" <tomonori.sakita@...d.co.jp>,
        "atsushi.nemoto@...d.co.jp" <atsushi.nemoto@...d.co.jp>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V2 2/5] tty: serial: fsl_lpuart: clear UARTCTRL_LOOPS in
 lpuart32_shutdown()



> -----Original Message-----
> From: Michael Walle <michael@...le.cc>
> Sent: 2022年11月23日 18:34
> To: Sherry Sun <sherry.sun@....com>
> Cc: gregkh@...uxfoundation.org; jirislaby@...nel.org;
> jingchang.lu@...escale.com; tomonori.sakita@...d.co.jp;
> atsushi.nemoto@...d.co.jp; linux-serial@...r.kernel.org; linux-
> kernel@...r.kernel.org; dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH V2 2/5] tty: serial: fsl_lpuart: clear UARTCTRL_LOOPS in
> lpuart32_shutdown()
> 
> Am 2022-11-10 09:17, schrieb Sherry Sun:
> > UARTCTRL_LOOPS bit is set in lpuart32_set_mctrl() for loopback mode,
> > but nowhere clear this bit, it should be cleared when closing the uart
> > port to avoid the loopback mode been enabled by default when reopening
> > the uart.
> 
> It's cleared in set_mctrl(). What is the expectation from the serial core here?
> 

Hi Michael,

If we call .set_mctrl(TIOCM_LOOP), the UARTCTRL_LOOPS will be set.
Then when we call .shutdown(), serial core won't call .set_mctrl() to clear it, so the UARTCTRL_LOOPS need to be cleared here.
Per my understanding, .shutdown() should clean up all the uart flags, as the transmitter and receiver will been disabled, we will re-configure all the settings needed when re-open the port.

Best Regards
Sherry