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

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Message-ID: <Y3eYX0qJkDEHhiSF@errol.ini.cmu.edu>
Date:   Fri, 18 Nov 2022 09:36:15 -0500
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.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 12/14] serial: liteuart: add IRQ support for the RX
 path

On Fri, Nov 18, 2022 at 04:30:15PM +0200, Ilpo Järvinen wrote:
> On Fri, 18 Nov 2022, Gabriel L. Somlo wrote:
> 
> > 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@...il.com>
> > > > ---
> > > > 
> > > > 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.
> 
> Also that pr_fmt() should be dropped (in case you didn't already). It was 
> in my mind ealier but should have stated it explicitly.

Understood. I've used dev_err() before, it just slipped my mind to
check for the availability of a `dev` field in `struct uart_port`...  :)

Thanks again for the review!

Best,
--Gabriel