Subject: [PATCH LINUX v3 08/10] tty: xuartps: Move RX path into helper function

From: [email-masked] (Peter Hurley)
Date: Sat, 5 Dec 2015 12:40:07 -0500

On 11/21/2015 09:59 PM, Soren Brinkmann wrote:
> Move RX-related IRQ handling into a helper function.
Fixes a problem where every char received after a parity or frame error
in the current isr will also be tagged as a parity or frame error.

Reviewed-by: Peter Hurley <[email-masked]>

NB: the sysrq problem in cdns_uart_isr() with needing to drop the
locks is because cdns_uart_console_write() tries to take the port->lock.
The 8250 driver handles this problem by not trying to take the
port->lock if port->sysrq is non-zero. See serial8250_console_write().

> Signed-off-by: Soren Brinkmann <[email-masked]>
> ---
>  drivers/tty/serial/xilinx_uartps.c | 50 +++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index f3ac69387b0a..db9e23eaf300 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -172,28 +172,8 @@ struct cdns_uart {
>  #define to_cdns_uart(_nb) container_of(_nb, struct cdns_uart, \
>  		clk_rate_change_nb);
>  
> -/**
> - * cdns_uart_isr - Interrupt handler
> - * @irq: Irq number
> - * @dev_id: Id of the port
> - *
> - * Return: IRQHANDLED
> - */
> -static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
> +static void cdns_uart_handle_rx(struct uart_port *port, unsigned int isrstatus)
>  {
> -	struct uart_port *port = (struct uart_port *)dev_id;
> -	unsigned long flags;
> -	unsigned int isrstatus, numbytes;
> -	unsigned int data;
> -	char status = TTY_NORMAL;

See, the previous code never reset the status back to TTY_NORMAL after any other
status.

> -
> -	spin_lock_irqsave(&port->lock, flags);
> -
> -	/* Read the interrupt status register to determine which
> -	 * interrupt(s) is/are active.
> -	 */
> -	isrstatus = readl(port->membase + CDNS_UART_ISR_OFFSET);
> -
>  	/*
>  	 * There is no hardware break detection, so we interpret framing
>  	 * error with all-zeros data as a break sequence. Most of the time,
> @@ -223,6 +203,9 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
>  		/* Receive Timeout Interrupt */
>  		while (!(readl(port->membase + CDNS_UART_SR_OFFSET) &
>  					CDNS_UART_SR_RXEMPTY)) {
> +			u32 data;
> +			char status = TTY_NORMAL;
> +
>  			data = readl(port->membase + CDNS_UART_FIFO_OFFSET);
>  
>  			/* Non-NULL byte after BREAK is garbage (99%) */
> @@ -263,10 +246,33 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
>  			}
>  
>  			uart_insert_char(port, isrstatus, CDNS_UART_IXR_OVERRUN,
> -					data, status);
> +					 data, status);
>  		}
>  		tty_flip_buffer_push(&port->state->port);
>  	}
> +}
> +
> +/**
> + * cdns_uart_isr - Interrupt handler
> + * @irq: Irq number
> + * @dev_id: Id of the port
> + *
> + * Return: IRQHANDLED
> + */
> +static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
> +{
> +	struct uart_port *port = (struct uart_port *)dev_id;
> +	unsigned long flags;
> +	unsigned int isrstatus, numbytes;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +
> +	/* Read the interrupt status register to determine which
> +	 * interrupt(s) is/are active.
> +	 */
> +	isrstatus = readl(port->membase + CDNS_UART_ISR_OFFSET);
> +
> +	cdns_uart_handle_rx(port, isrstatus);
>  
>  	/* Dispatch an appropriate handler */
>  	if ((isrstatus & CDNS_UART_IXR_TXEMPTY) == CDNS_UART_IXR_TXEMPTY) {
>