[PATCH] serial: uartps: Wait for tx_empty in console setup

[PATCH] serial: uartps: Wait for tx_empty in console setup

[Raviteja Narayanam]

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@xilinx.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 */
-- 
2.7.4


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Re: [PATCH] serial: uartps: Wait for tx_empty in console setup

[Shubhrajyoti Datta]

Hi ,
On Tue, Apr 7, 2020 at 10:25 PM Raviteja Narayanam
<raviteja.narayanam@xilinx.com> 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.
>
Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>

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Re: [PATCH] serial: uartps: Wait for tx_empty in console setup

[Maarten Brock]

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@xilinx.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.

Maarten


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RE: [PATCH] serial: uartps: Wait for tx_empty in console setup

[Raviteja Narayanam]

Hi Maarten,

Thanks for the review.

> -----Original Message-----
> From: linux-serial-owner@vger.kernel.org <linux-serial-
> owner@vger.kernel.org> On Behalf Of Maarten Brock
> Sent: Wednesday, April 8, 2020 9:21 PM
> To: Raviteja Narayanam <rna@xilinx.com>
> Cc: linux-serial@vger.kernel.org; gregkh@linuxfoundation.org;
> jslaby@suse.com; Michal Simek <michals@xilinx.com>; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; git <git@xilinx.com>;
> linux-serial-owner@vger.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@xilinx.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

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