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

[Gabriel L. Somlo]

On Fri, Nov 18, 2022 at 03:58:47PM +0200, Ilpo Järvinen wrote:
> 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.

Makes sense, good thing `struct uart_port` has a `dev` field :)
I've made the change, and lined it up for the upcoming v5 of the
series.
 
> > +			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.

Removed in v5.

> Other than that,
> 
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

Thanks much, I'll send out v5 a bit later today.

--Gabriel

> -- 
>  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;
> >