linux-kernel - RE: [PATCH] serial: uartps: Wait for tx

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Message-ID: <SN4PR0201MB3486FECBFEA2271F2C6D0EA9CAC10@SN4PR0201MB3486.namprd02.prod.outlook.com>
Date:   Thu, 9 Apr 2020 05:39:18 +0000
From:   Raviteja Narayanam <rna@...inx.com>
To:     Maarten Brock <m.brock@...mierlo.com>
CC:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jslaby@...e.com" <jslaby@...e.com>,
        Michal Simek <michals@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git <git@...inx.com>,
        "linux-serial-owner@...r.kernel.org" 
        <linux-serial-owner@...r.kernel.org>
Subject: RE: [PATCH] serial: uartps: Wait for tx_empty in console setup

Hi Maarten,

Thanks for the review.

> -----Original Message-----
> From: linux-serial-owner@...r.kernel.org <linux-serial-
> owner@...r.kernel.org> On Behalf Of Maarten Brock
> Sent: Wednesday, April 8, 2020 9:21 PM
> To: Raviteja Narayanam <rna@...inx.com>
> Cc: linux-serial@...r.kernel.org; gregkh@...uxfoundation.org;
> jslaby@...e.com; Michal Simek <michals@...inx.com>; linux-arm-
> kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; git <git@...inx.com>;
> linux-serial-owner@...r.kernel.org
> Subject: Re: [PATCH] serial: uartps: Wait for tx_empty in console setup
> 
> On 2020-04-07 18:53, Raviteja Narayanam wrote:
> > On some platforms, the log is corrupted while console is being
> > registered. It is observed that when set_termios is called, there are
> > still some bytes in the FIFO to be transmitted.
> >
> > So, wait for tx_empty inside cdns_uart_console_setup before calling
> > set_termios.
> >
> > Signed-off-by: Raviteja Narayanam <raviteja.narayanam@...inx.com>
> > ---
> >  drivers/tty/serial/xilinx_uartps.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/tty/serial/xilinx_uartps.c
> > b/drivers/tty/serial/xilinx_uartps.c
> > index 6b26f76..23468ff 100644
> > --- a/drivers/tty/serial/xilinx_uartps.c
> > +++ b/drivers/tty/serial/xilinx_uartps.c
> > @@ -1260,6 +1260,8 @@ static int cdns_uart_console_setup(struct
> > console *co, char *options)
> >  	int bits = 8;
> >  	int parity = 'n';
> >  	int flow = 'n';
> > +	unsigned long time_out = jiffies + usecs_to_jiffies(TX_TIMEOUT);
> > +	int status;
> >
> >  	if (!port->membase) {
> >  		pr_debug("console on " CDNS_UART_TTY_NAME "%i not
> present\n", @@
> > -1270,6 +1272,14 @@ static int cdns_uart_console_setup(struct console
> > *co, char *options)
> >  	if (options)
> >  		uart_parse_options(options, &baud, &parity, &bits, &flow);
> >
> > +	/* Wait for tx_empty before setting up the console */
> > +	while (time_before(jiffies, time_out)) {
> > +		status = cdns_uart_tx_empty(port);
> > +		if (status == TIOCSER_TEMT)
> > +			break;
> > +		cpu_relax();
> > +	}
> > +
> >  	return uart_set_options(port, co, baud, parity, bits, flow);  }
> > #endif /* CONFIG_SERIAL_XILINX_PS_UART_CONSOLE */
> 
> You could do without the status variable. You could even combine the while
> and if conditions.
> 
> And while you're at it, you might as well also rewrite the lines
> 1236-1238 to also use cdns_uart_tx_empty() for clarity.

Will send v2, addressing these.
> 
> Maarten

Regards,
Raviteja N