linux-kernel - RE: [PATCH 2/2] tty: serial: fsl_lpuart: improve lpuart32 registers clearing when shutdown

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Date:   Thu, 10 Nov 2022 03:32:48 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 2/2] tty: serial: fsl_lpuart: improve lpuart32 registers
 clearing when shutdown



> -----Original Message-----
> From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Sent: 2022年11月9日 20:19
> To: Sherry Sun <sherry.sun@....com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Jiri Slaby
> <jirislaby@...nel.org>; linux-serial <linux-serial@...r.kernel.org>; LKML
> <linux-kernel@...r.kernel.org>; dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH 2/2] tty: serial: fsl_lpuart: improve lpuart32 registers
> clearing when shutdown
> 
> On Wed, 9 Nov 2022, Sherry Sun wrote:
> 
> > Need to clear the UARTSTAT and UARTMODIR registers when shutdown the
> > uart port, also clear the Rx/Tx DMA enable bits and loopback
> > configuration bit.
> 
> This lacks answer to "Why?" question. Think about somebody not as familiar
> with the HW as you are looking back to this very commit message like 5 years
> from now and wondering why this change was made.
> 
> Preferrably make a separate change out of all these four changes if the
> answers to why question are different.
> 
> It would also help in deciding whether Fixes tag is necessary or not since you
> didn't seem to include.

Hi Ilpo,

Ok, maybe I need to separate the four changes in lpuart32_shutdown() to better describe the "why". Thanks for the comments.

Best Regards
Sherry


> 
> --
>  i.
> 
> > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > ---
> >  drivers/tty/serial/fsl_lpuart.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c index f5a0a14fa366..43d9d6a6e94a
> > 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -1771,11 +1771,22 @@ static void lpuart32_shutdown(struct
> uart_port
> > *port)
> >
> >  	spin_lock_irqsave(&port->lock, flags);
> >
> > +	/* clear statue */
> > +	temp = lpuart32_read(&sport->port, UARTSTAT);
> > +	lpuart32_write(&sport->port, temp, UARTSTAT);
> > +
> > +	/* disable Rx/Tx DMA */
> > +	temp = lpuart32_read(port, UARTBAUD);
> > +	temp &= ~(UARTBAUD_TDMAE | UARTBAUD_RDMAE);
> > +	lpuart32_write(port, temp, UARTBAUD);
> > +
> >  	/* disable Rx/Tx and interrupts */
> >  	temp = lpuart32_read(port, UARTCTRL);
> >  	temp &= ~(UARTCTRL_TE | UARTCTRL_RE | UARTCTRL_ILIE |
> > -			UARTCTRL_TIE | UARTCTRL_TCIE | UARTCTRL_RIE);
> > +			UARTCTRL_TIE | UARTCTRL_TCIE | UARTCTRL_RIE |
> > +			UARTCTRL_LOOPS);
> >  	lpuart32_write(port, temp, UARTCTRL);
> > +	lpuart32_write(port, 0, UARTMODIR);
> >
> >  	spin_unlock_irqrestore(&port->lock, flags);
> >
> >