linux-kernel - Re: [External Email] Re: [PATCH] serial: sc16is7xx: Add polling feature if no IRQ usage possible

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Message-ID: <fbd224a3-8f10-3ccf-5480-38fcd839d409@systec-electronic.com>
Date: Thu, 19 Dec 2024 10:22:40 +0100 (CET)
From: Andre Werner <andre.werner@...tec-electronic.com>
To: Greg KH <gregkh@...uxfoundation.org>
cc: Andre Werner <andre.werner@...tec-electronic.com>, jirislaby@...nel.org, 
    hvilleneuve@...onoff.com, andy@...nel.org, linux-kernel@...r.kernel.org, 
    linux-serial@...r.kernel.org, lech.perczak@...lingroup.com
Subject: Re: [External Email] Re: [PATCH] serial: sc16is7xx: Add polling
 feature if no IRQ usage possible

Dear Greg,
On Thu, 19 Dec 2024, Greg KH wrote:

> On Thu, Dec 19, 2024 at 09:46:38AM +0100, Andre Werner wrote:
> > Fall back to polling mode if no interrupt is configured because not
> > possible. If "interrupts" property is missing in devicetree the driver
> > uses a delayed worker to pull state of interrupt status registers.
> >
> > Signed-off-by: Andre Werner <andre.werner@...tec-electronic.com>
> > ---
> > This driver was tested on Linux 5.10. We had a custom board that was not
> > able to connect the interrupt port. Only I2C was available.
>
> Could you not test this on the latest tree?  5.10 is _VERY_ old now.

I will try it on devboard with a 6.1 Kernel. Is that okay for you?

>
> > ---
> > ---
> >  drivers/tty/serial/sc16is7xx.c | 40 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 40 insertions(+)
> >
> > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> > index a3093e09309f..31962fdca178 100644
> > --- a/drivers/tty/serial/sc16is7xx.c
> > +++ b/drivers/tty/serial/sc16is7xx.c
> > @@ -314,6 +314,7 @@
> >  #define SC16IS7XX_FIFO_SIZE		(64)
> >  #define SC16IS7XX_GPIOS_PER_BANK	4
> >
> > +#define SC16IS7XX_POLL_PERIOD 10 /*ms*/
>
> Please use a tab here.
>
> >  #define SC16IS7XX_RECONF_MD		BIT(0)
> >  #define SC16IS7XX_RECONF_IER		BIT(1)
> >  #define SC16IS7XX_RECONF_RS485		BIT(2)
> > @@ -348,6 +349,9 @@ struct sc16is7xx_port {
> >  	u8				mctrl_mask;
> >  	struct kthread_worker		kworker;
> >  	struct task_struct		*kworker_task;
> > +	struct kthread_delayed_work	poll_work;
> > +	bool polling;
> > +	bool shutdown;
> >  	struct sc16is7xx_one		p[];
> >  };
> >
> > @@ -861,6 +865,19 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
> >  	return IRQ_HANDLED;
> >  }
> >
> > +static void sc16is7xx_transmission_poll(struct kthread_work *work)
> > +{
> > +	struct sc16is7xx_port *s = container_of(work, struct sc16is7xx_port, poll_work.work);
> > +
> > +	/* Resuse standard IRQ handler. Interrupt ID is unused in this context. */
> > +	sc16is7xx_irq(0, s);
> > +
> > +	/* setup delay based on SC16IS7XX_POLL_PERIOD */
> > +	if (!s->shutdown)
> > +		kthread_queue_delayed_work(&s->kworker, &s->poll_work,
> > +					   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD));
> > +}
> > +
> >  static void sc16is7xx_tx_proc(struct kthread_work *ws)
> >  {
> >  	struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port);
> > @@ -1149,6 +1166,7 @@ static int sc16is7xx_config_rs485(struct uart_port *port, struct ktermios *termi
> >  static int sc16is7xx_startup(struct uart_port *port)
> >  {
> >  	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
> > +	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
> >  	unsigned int val;
> >  	unsigned long flags;
> >
> > @@ -1210,6 +1228,11 @@ static int sc16is7xx_startup(struct uart_port *port)
> >  	uart_port_lock_irqsave(port, &flags);
> >  	sc16is7xx_enable_ms(port);
> >  	uart_port_unlock_irqrestore(port, flags);
> > +	if (s->polling) {
> > +		s->shutdown = false;
> > +		kthread_queue_delayed_work(&s->kworker, &s->poll_work,
> > +					   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD));
> > +	}
> >
> >  	return 0;
> >  }
> > @@ -1232,6 +1255,10 @@ static void sc16is7xx_shutdown(struct uart_port *port)
> >
> >  	sc16is7xx_power(port, 0);
> >
> > +	if (s->polling) {
> > +		s->shutdown = true;
> > +		kthread_cancel_delayed_work_sync(&s->poll_work);
> > +	}
> >  	kthread_flush_worker(&s->kworker);
> >  }
> >
> > @@ -1537,7 +1564,13 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
> >
> >  	/* Always ask for fixed clock rate from a property. */
> >  	device_property_read_u32(dev, "clock-frequency", &uartclk);
> > +	s->polling = !device_property_present(dev, "interrupts");
> >
> > +	if (s->polling) {
> > +		dev_warn(dev,
> > +			 "No interrupt definition found. Falling back to polling mode.\n");
>
> What is a user supposed to do with this message?  And why would a device
> NOT have any interrupts?  This feels like it is just going to pound on
> the device and cause a lot of power drain for just a simple little uart.

I thought it could be interesting to know that the device has missing
interrupt support.

>
> Why can't your system provide a valid irq line?
>

In our case we have only an I2C available in a connection cable and the
GPIOs are linked through a two way level shifter.
It was a very special situation in our case because target platform and
sensor platform are provided.
The IRQ from the sensor war not able to drive the two way level shifter low so
we always detect outgoing traffic and the IRQ signal but at the target
board after the level shifter the signal remains stable. So
communication failed with a timeout. So we need to force polling the
interrupt status register because
both HW solution should not be changed in any way.

> thanks,
>
> greg k-h
>


Regards, André