Re: [PATCHv2 2/2] serial: uartps: Add a timeout to the tx empty wait

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On Tue, May 21, 2019 at 04:33:38PM +0530, shubhrajyoti.datta@xxxxxxxxx wrote:
> From: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>
> 
> In case the cable is not connected then the target gets into
> a infinite wait for tx empty.
> Add a timeout to the tx empty wait.
> 
> Reported-by: Jean-Francois Dagenais <jeff.dagenais@xxxxxxxxx>
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>
> ---
>  drivers/tty/serial/xilinx_uartps.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index 8850790..dc86511 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -26,12 +26,14 @@
>  #include <linux/of.h>
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/iopoll.h>
>  
>  #define CDNS_UART_TTY_NAME	"ttyPS"
>  #define CDNS_UART_NAME		"xuartps"
>  #define CDNS_UART_MAJOR		0	/* use dynamic node allocation */
>  #define CDNS_UART_FIFO_SIZE	64	/* FIFO size */
>  #define CDNS_UART_REGISTER_SPACE	0x1000
> +#define TX_TIMEOUT		500000
>  
>  /* Rx Trigger level */
>  static int rx_trigger_level = 56;
> @@ -688,14 +690,18 @@ static void cdns_uart_set_termios(struct uart_port *port,
>  	unsigned int cval = 0;
>  	unsigned int baud, minbaud, maxbaud;
>  	unsigned long flags;
> -	unsigned int ctrl_reg, mode_reg;
> +	unsigned int ctrl_reg, mode_reg, val;
> +	int err;
>  
>  	/* Wait for the transmit FIFO to empty before making changes */
>  	if (!(readl(port->membase + CDNS_UART_CR) &
>  				CDNS_UART_CR_TX_DIS)) {
> -		while (!(readl(port->membase + CDNS_UART_SR) &
> -				CDNS_UART_SR_TXEMPTY)) {
> -			cpu_relax();
> +		err = readl_poll_timeout(port->membase + CDNS_UART_SR,
> +					 val, (val & CDNS_UART_SR_TXEMPTY),
> +					 1000, TX_TIMEOUT);
> +		if (err) {
> +			dev_info(port->dev, "timed out waiting for tx empty");
> +			return;

Also, shouldn't this be an error?  Why not tell the caller something
went wrong?

thanks,

greg k-h



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