linux-kernel - Re: [PATCH v4 13/14] serial: liteuart: add IRQ support for the TX path

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Date:   Fri, 18 Nov 2022 16:01:53 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Gabriel Somlo <gsomlo@...il.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, kgugala@...micro.com,
        mholenko@...micro.com, joel@....id.au,
        david.abdurachmanov@...il.com, florent@...oy-digital.fr,
        geert@...ux-m68k.org
Subject: Re: [PATCH v4 13/14] serial: liteuart: add IRQ support for the TX
 path

On Wed, 16 Nov 2022, Gabriel Somlo wrote:

> Switch the TX path to IRQ-driven operation, while maintaining support
> for polling mode via the poll timer.
> 
> Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> ---
> 
> Changes from v3:
>   - remove superfluous curly braces from liteuart_interrupt()
>   - simplified [start|stop]_tx() by using shadow irq register from
>     patch 12/14
>   - simplified liteuart_tx_chars() by rebasing on top of tty-next tree
> 
>  drivers/tty/serial/liteuart.c | 30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index fad778578986..977fc4349b47 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -93,27 +93,12 @@ static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 mask)
>  
>  static void liteuart_stop_tx(struct uart_port *port)
>  {
> +	liteuart_update_irq_reg(port, false, EV_TX);
>  }
>  
>  static void liteuart_start_tx(struct uart_port *port)
>  {
> -	struct circ_buf *xmit = &port->state->xmit;
> -	unsigned char ch;
> -
> -	if (unlikely(port->x_char)) {
> -		litex_write8(port->membase + OFF_RXTX, port->x_char);
> -		port->icount.tx++;
> -		port->x_char = 0;
> -	} else if (!uart_circ_empty(xmit)) {
> -		while (xmit->head != xmit->tail) {
> -			ch = xmit->buf[xmit->tail];
> -			uart_xmit_advance(port, 1);
> -			liteuart_putchar(port, ch);
> -		}
> -	}
> -
> -	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> -		uart_write_wakeup(port);
> +	liteuart_update_irq_reg(port, true, EV_TX);
>  }
>  
>  static void liteuart_stop_rx(struct uart_port *port)
> @@ -144,6 +129,15 @@ static void liteuart_rx_chars(struct uart_port *port)
>  	tty_flip_buffer_push(&port->state->port);
>  }
>  
> +static void liteuart_tx_chars(struct uart_port *port)
> +{
> +	u8 ch;
> +
> +	uart_port_tx(port, ch,
> +		!litex_read8(port->membase + OFF_TXFULL),
> +		litex_write8(port->membase + OFF_RXTX, ch));
> +}
> +
>  static irqreturn_t liteuart_interrupt(int irq, void *data)
>  {
>  	struct liteuart_port *uart = data;
> @@ -154,6 +148,8 @@ static irqreturn_t liteuart_interrupt(int irq, void *data)
>  	isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
>  	if (isr & EV_RX)
>  		liteuart_rx_chars(port);
> +	if (isr & EV_TX)
> +		liteuart_tx_chars(port);
>  	spin_unlock(&port->lock);
>  
>  	return IRQ_RETVAL(isr);

Looks very clean now with uart_port_tx(), thanks.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.