linux-kernel - Re: [PATCH v3 12/14] serial: liteuart: add IRQ support for the RX path

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Date:   Tue, 15 Nov 2022 18:00:11 +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 v3 12/14] serial: liteuart: add IRQ support for the RX
 path

On Sat, 12 Nov 2022, Gabriel Somlo wrote:

> Add support for IRQ-driven RX. Support for the TX path will be added
> in a separate commit.
> 
> Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> ---
>  drivers/tty/serial/liteuart.c | 61 +++++++++++++++++++++++++++++++----
>  1 file changed, 54 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index cf1ce597b45e..e30adb30277f 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <linux/console.h>
> +#include <linux/interrupt.h>
>  #include <linux/litex.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -130,13 +131,29 @@ static void liteuart_rx_chars(struct uart_port *port)
>  	tty_flip_buffer_push(&port->state->port);
>  }
>  
> +static irqreturn_t liteuart_interrupt(int irq, void *data)
> +{
> +	struct liteuart_port *uart = data;
> +	struct uart_port *port = &uart->port;
> +	u8 isr = litex_read8(port->membase + OFF_EV_PENDING);
> +
> +	/* for now, only rx path triggers interrupts */

Please don't add comment like this at all when your series removes it in a 
later patch.

> +	isr &= EV_RX;
> +
> +	spin_lock(&port->lock);
> +	if (isr & EV_RX)
> +		liteuart_rx_chars(port);
> +	spin_unlock(&port->lock);
> +
> +	return IRQ_RETVAL(isr);
> +}
> +
>  static void liteuart_timer(struct timer_list *t)
>  {
>  	struct liteuart_port *uart = from_timer(uart, t, timer);
>  	struct uart_port *port = &uart->port;
>  
> -	liteuart_rx_chars(port);
> -
> +	liteuart_interrupt(0, port);
>  	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
>  }
>  
> @@ -162,19 +179,42 @@ static unsigned int liteuart_get_mctrl(struct uart_port *port)
>  static int liteuart_startup(struct uart_port *port)
>  {
>  	struct liteuart_port *uart = to_liteuart_port(port);
> +	int ret;
> +	u8 irq_mask = 0;
>  
> -	/* disable events */
> -	litex_write8(port->membase + OFF_EV_ENABLE, 0);
> +	if (port->irq) {
> +		ret = request_irq(port->irq, liteuart_interrupt, 0,
> +				  KBUILD_MODNAME, uart);
> +		if (ret == 0) {
> +			/* only enable rx interrupts at this time */

This comment seems pretty useless. Your code says very much the same.

-- 
 i.

> +			irq_mask = EV_RX;
> +		} else {
> +			pr_err(pr_fmt("line %d irq %d failed: using polling\n"),
> +				port->line, port->irq);
> +			port->irq = 0;
> +		}
> +	}
>  
> -	/* prepare timer for polling */
> -	timer_setup(&uart->timer, liteuart_timer, 0);
> -	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +	if (!port->irq) {
> +		timer_setup(&uart->timer, liteuart_timer, 0);
> +		mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +	}
> +
> +	litex_write8(port->membase + OFF_EV_ENABLE, irq_mask);
>  
>  	return 0;
>  }
>  
>  static void liteuart_shutdown(struct uart_port *port)
>  {
> +	struct liteuart_port *uart = to_liteuart_port(port);
> +
> +	litex_write8(port->membase + OFF_EV_ENABLE, 0);
> +
> +	if (port->irq)
> +		free_irq(port->irq, port);
> +	else
> +		del_timer_sync(&uart->timer);
>  }
>  
>  static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
> @@ -263,6 +303,13 @@ static int liteuart_probe(struct platform_device *pdev)
>  		goto err_erase_id;
>  	}
>  
> +	/* get irq */
> +	ret = platform_get_irq_optional(pdev, 0);
> +	if (ret < 0 && ret != -ENXIO)
> +		return ret;
> +	if (ret > 0)
> +		port->irq = ret;
> +
>  	/* values not from device tree */
>  	port->dev = &pdev->dev;
>  	port->iotype = UPIO_MEM;
>