linux-kernel - RE: [PATCH 06/14] serial: tegra: report error to upper tty layer

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Message-ID: <SN6PR12MB273439430F80C358B6DB663DC3A00@SN6PR12MB2734.namprd12.prod.outlook.com>
Date:   Tue, 27 Aug 2019 09:29:44 +0000
From:   Krishna Yarlagadda <kyarlagadda@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "Laxman Dewangan" <ldewangan@...dia.com>,
        "jslaby@...e.com" <jslaby@...e.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Shardar Mohammed" <smohammed@...dia.com>
Subject: RE: [PATCH 06/14] serial: tegra: report error to upper tty layer

> -----Original Message-----
> From: Thierry Reding <thierry.reding@...il.com>
> Sent: Tuesday, August 13, 2019 3:22 PM
> To: Krishna Yarlagadda <kyarlagadda@...dia.com>
> Cc: gregkh@...uxfoundation.org; robh+dt@...nel.org; 
> mark.rutland@....com; Jonathan Hunter <jonathanh@...dia.com>; Laxman 
> Dewangan <ldewangan@...dia.com>; jslaby@...e.com; linux- 
> serial@...r.kernel.org; devicetree@...r.kernel.org; linux- 
> tegra@...r.kernel.org; linux-kernel@...r.kernel.org; Shardar Mohammed 
> <smohammed@...dia.com>
> Subject: Re: [PATCH 06/14] serial: tegra: report error to upper tty 
> layer
> 
> On Mon, Aug 12, 2019 at 04:58:15PM +0530, Krishna Yarlagadda wrote:
> > Report overrun/parity/frame/break errors to top tty layer. Add 
> > support to ignore break character if IGNBRK is set.
> >
> > Signed-off-by: Shardar Shariff Md <smohammed@...dia.com>
> > Signed-off-by: Krishna Yarlagadda <kyarlagadda@...dia.com>
> > ---
> >  drivers/tty/serial/serial-tegra.c | 19 ++++++++++++++++---
> >  1 file changed, 16 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/serial/serial-tegra.c
> > b/drivers/tty/serial/serial-tegra.c
> > index f6a3f4e..7ab81bb 100644
> > --- a/drivers/tty/serial/serial-tegra.c
> > +++ b/drivers/tty/serial/serial-tegra.c
> > @@ -374,13 +374,21 @@ static char tegra_uart_decode_rx_error(struct
> tegra_uart_port *tup,
> >  			tup->uport.icount.frame++;
> >  			dev_err(tup->uport.dev, "Got frame errors\n");
> >  		} else if (lsr & UART_LSR_BI) {
> > -			dev_err(tup->uport.dev, "Got Break\n");
> > -			tup->uport.icount.brk++;
> > -			/* If FIFO read error without any data, reset Rx FIFO
> */
> > +			/*
> > +			 * Break error
> > +			 * If FIFO read error without any data, reset Rx FIFO
> > +			 */
> >  			if (!(lsr & UART_LSR_DR) && (lsr & UART_LSR_FIFOE))
> >  				tegra_uart_fifo_reset(tup,
> UART_FCR_CLEAR_RCVR);
> > +			if (tup->uport.ignore_status_mask & UART_LSR_BI)
> > +				return TTY_BREAK;
> > +			flag = TTY_BREAK;
> > +			tup->uport.icount.brk++;
> > +			dev_err(tup->uport.dev, "Got Break\n");
> 
> I know this is preexisting, but why do we want to output an error 
> message in these cases. Isn't it perfectly legal for this to happen?
> 
> Thierry
> 
It is valid to have breaks for sysrq requests. But they also indicate possible mismatch in baud rate. So warning user as this could be potential issue. I will change this to dev_dbg to avoid spamming user in valid cases.

KY
> >  		}
> > +		uart_insert_char(&tup->uport, lsr, UART_LSR_OE, 0, flag);
> >  	}
> > +
> >  	return flag;
> >  }
> >
> > @@ -562,6 +570,9 @@ static void tegra_uart_handle_rx_pio(struct
> tegra_uart_port *tup,
> >  			break;
> >
> >  		flag = tegra_uart_decode_rx_error(tup, lsr);
> > +		if (flag != TTY_NORMAL)
> > +			continue;
> > +
> >  		ch = (unsigned char) tegra_uart_read(tup, UART_RX);
> >  		tup->uport.icount.rx++;
> >
> > @@ -1224,6 +1235,8 @@ static void tegra_uart_set_termios(struct
> uart_port *u,
> >  	/* Ignore all characters if CREAD is not set */
> >  	if ((termios->c_cflag & CREAD) == 0)
> >  		tup->uport.ignore_status_mask |= UART_LSR_DR;
> > +	if (termios->c_iflag & IGNBRK)
> > +		tup->uport.ignore_status_mask |= UART_LSR_BI;
> >
> >  	spin_unlock_irqrestore(&u->lock, flags);  }
> > --
> > 2.7.4
> >