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

["Gabriel L. Somlo" <gsomlo@gmail.com>]

On Tue, Nov 15, 2022 at 06:21:00PM +0200, Ilpo Järvinen wrote:
> On Tue, 15 Nov 2022, Gabriel L. Somlo wrote:
> 
> > On Tue, Nov 15, 2022 at 06:00:11PM +0200, Ilpo Järvinen wrote:
> > > 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@gmail.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.
> > 
> > OK, I will remove it in v4.
> > 
> > > > +	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.
> > 
> > The comment was meant to let the reader know that the code is doing it
> > *intentionally* (rather than forgetting to enable tx irqs by mistake).
> > But I'm OK with removing this comment in v4 as well if you think
> > that's an overly paranoid and redundant thing to do... :)
> 
> I see. Reading the other comment first caused me to misinterpret this one 
> to mean that only RX interrupts are implemented.
> 
> Maybe if you change "at this time" to "at startup" it would make it more 
> obvious.
 
OK, I'll fix the comment per your suggestion rather than get rid of it.

Thanks again,
--G

> -- 
>  i.