Re: [PATCH v4 12/14] serial: liteuart: add IRQ support for the RX path

[Ilpo Järvinen]

On Wed, 16 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@xxxxxxxxx>
> ---
> 
> Changes from v3:
>   - add shadow irq register to support polling mode and avoid reading
>     hardware mmio irq register to learn which irq flags are enabled
>     - this also simplifies both liteuart_interrupt() and liteuart_startup()
> 
>  drivers/tty/serial/liteuart.c | 76 +++++++++++++++++++++++++++++++----
>  1 file changed, 69 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index 8a6e176be08e..fad778578986 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/bits.h>
>  #include <linux/console.h>
> +#include <linux/interrupt.h>
>  #include <linux/litex.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -46,6 +47,7 @@ struct liteuart_port {
>  	struct uart_port port;
>  	struct timer_list timer;
>  	u32 id;
> +	u8 irq_reg;
>  };
>  
>  #define to_liteuart_port(port)	container_of(port, struct liteuart_port, port)
> @@ -76,6 +78,19 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)
>  	litex_write8(port->membase + OFF_RXTX, ch);
>  }
>  
> +static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 mask)
> +{
> +	struct liteuart_port *uart = to_liteuart_port(port);
> +
> +	if (set)
> +		uart->irq_reg |= mask;
> +	else
> +		uart->irq_reg &= ~mask;
> +
> +	if (port->irq)
> +		litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
> +}
> +
>  static void liteuart_stop_tx(struct uart_port *port)
>  {
>  }
> @@ -129,13 +144,27 @@ 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;
> +
> +	spin_lock(&port->lock);
> +	isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
> +	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));
>  }
>  
> @@ -161,19 +190,45 @@ 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);
> +	unsigned long flags;
> +	int ret;
>  
> -	/* 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) {
> +			pr_err(pr_fmt("line %d irq %d failed: using polling\n"),
> +				port->line, port->irq);

dev_err() seems more appropriate here.

> +			port->irq = 0;
> +		}
> +	}
>  
> -	/* prepare timer for polling */
> -	timer_setup(&uart->timer, liteuart_timer, 0);
> -	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +	spin_lock_irqsave(&port->lock, flags);
> +	/* only enabling rx irqs during startup */
> +	liteuart_update_irq_reg(port, true, EV_RX);
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	if (!port->irq) {
> +		timer_setup(&uart->timer, liteuart_timer, 0);
> +		mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +	}
>  
>  	return 0;
>  }
>  
>  static void liteuart_shutdown(struct uart_port *port)
>  {
> +	struct liteuart_port *uart = to_liteuart_port(port);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +	liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	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,
> @@ -262,6 +317,13 @@ static int liteuart_probe(struct platform_device *pdev)
>  		goto err_erase_id;
>  	}
>  
> +	/* get irq */

This comment is unnecessary.

Other than that,

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

-- 
 i.


> +	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;
>