[PATCH v2 0/2] serial: uartps: Add tx_empty checks

[PATCH v2 0/2] serial: uartps: Add tx_empty checks

[Raviteja Narayanam]

This patch series does the following:
Use cdns_uart_tx_empty function in the driver.
Wait for empty.

v2:
Modified the wait in console setup and used cdns_uart_tx_empty function
in console_write as suggested by Maarten.

Raviteja Narayanam (2):
  serial: uartps: Wait for tx_empty in console setup
  serial: uartps: Use cdns_uart_tx_empty in console_write

 drivers/tty/serial/xilinx_uartps.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

-- 
2.7.4

[PATCH v2 1/2] 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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 6b26f76..0bf946b 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1260,6 +1260,7 @@ static int cdns_uart_console_setup(struct console *co, char *options)
 	int bits = 8;
 	int parity = 'n';
 	int flow = 'n';
+	unsigned long time_out;
 
 	if (!port->membase) {
 		pr_debug("console on " CDNS_UART_TTY_NAME "%i not present\n",
@@ -1270,6 +1271,13 @@ 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 */
+	time_out = jiffies + usecs_to_jiffies(TX_TIMEOUT);
+
+	while (time_before(jiffies, time_out) &&
+	       cdns_uart_tx_empty(port) != TIOCSER_TEMT)
+		cpu_relax();
+
 	return uart_set_options(port, co, baud, parity, bits, flow);
 }
 #endif /* CONFIG_SERIAL_XILINX_PS_UART_CONSOLE */
-- 
2.7.4

[PATCH v2 2/2] serial: uartps: Use cdns_uart_tx_empty in console_write

[Raviteja Narayanam]

Instead of accessing the registers and checking for tx_empty,
use cdns_uart_tx_empty in cdns_uart_console_write function.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
---
 drivers/tty/serial/xilinx_uartps.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 0bf946b..042aa6f 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1233,9 +1233,7 @@ static void cdns_uart_console_write(struct console *co, const char *s,
 	writel(ctrl, port->membase + CDNS_UART_CR);
 
 	uart_console_write(port, s, count, cdns_uart_console_putchar);
-	while ((readl(port->membase + CDNS_UART_SR) &
-			(CDNS_UART_SR_TXEMPTY | CDNS_UART_SR_TACTIVE)) !=
-			CDNS_UART_SR_TXEMPTY)
+	while (cdns_uart_tx_empty(port) != TIOCSER_TEMT)
 		cpu_relax();
 
 	/* restore interrupt state */
-- 
2.7.4

Re: [PATCH v2 0/2] serial: uartps: Add tx_empty checks

[Shubhrajyoti Datta]

Hi Raviteja,
thanks for the patch.

On Thu, Apr 9, 2020 at 11:59 AM Raviteja Narayanam
<raviteja.narayanam@xilinx.com> wrote:
>
> This patch series does the following:
> Use cdns_uart_tx_empty function in the driver.
> Wait for empty.
>
> v2:
> Modified the wait in console setup and used cdns_uart_tx_empty function
> in console_write as suggested by Maarten.
>
Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>

> Raviteja Narayanam (2):
>   serial: uartps: Wait for tx_empty in console setup
>   serial: uartps: Use cdns_uart_tx_empty in console_write
>
>  drivers/tty/serial/xilinx_uartps.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> --
> 2.7.4
>