linux-kernel - Re: [PATCH v4 2/2] serial: sc16is7xx: Add polling mode if no IRQ pin is available

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Message-Id: <20250109094303.9c1917e2e8704ff265dac4e2@hugovil.com>
Date: Thu, 9 Jan 2025 09:43:03 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: Andre Werner <andre.werner@...tec-electronic.com>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org,
 hvilleneuve@...onoff.com, andy@...nel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
 lech.perczak@...lingroup.com, krzk+dt@...nel.org, conor+dt@...nel.org,
 robh@...nel.org
Subject: Re: [PATCH v4 2/2] serial: sc16is7xx: Add polling mode if no IRQ
 pin is available

Hi Andre,

On Thu,  9 Jan 2025 10:38:34 +0100
Andre Werner <andre.werner@...tec-electronic.com> wrote:

> Fall back to polling mode if no interrupt is configured because there
> is no possibility to connect the interrupt pin.
> If "interrupts" property is missing in devicetree the driver
> uses a delayed worker to pull the state of interrupt status registers.
> 
> Signed-off-by: Andre Werner <andre.werner@...tec-electronic.com>
> ---
> V2:
> - Change warning for polling mode to debug log entry
> - Correct typo: Resuse -> Reuse
> - Format define with missing tabs for SC16IS7XX_POLL_PERIOD
> - Format struct declaration sc16is7xx_one_config with missing tabs for polling and shutdown
> - Adapt dtbinding with new polling feature
> V3:
> - Use suffix with units and drop a comment SC16IS7XX_POLL_PERIOD_MS. Sorry for that miss.
> - Make Kernel lowercase.
> V4:
> - Reword commit messages for better understanding.
> - Remove 'shutdown' property for canceling delayed worker.
> - Rename worker function: sc16is7xx_transmission_poll -> sc16is7xx_poll_proc
> - Unify argument for worker functions: kthread_work *work -> kthread_work *ws
> ---
>  drivers/tty/serial/sc16is7xx.c | 38 ++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> index a3093e09309f..6645cab2ae5f 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_MS	10
>  #define SC16IS7XX_RECONF_MD		BIT(0)
>  #define SC16IS7XX_RECONF_IER		BIT(1)
>  #define SC16IS7XX_RECONF_RS485		BIT(2)
> @@ -348,6 +349,8 @@ struct sc16is7xx_port {
>  	u8				mctrl_mask;
>  	struct kthread_worker		kworker;
>  	struct task_struct		*kworker_task;
> +	struct kthread_delayed_work	poll_work;
> +	bool				polling;
>  	struct sc16is7xx_one		p[];
>  };
>  
> @@ -861,6 +864,18 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
>  	return IRQ_HANDLED;
>  }
>  
> +static void sc16is7xx_poll_proc(struct kthread_work *ws)
> +{
> +	struct sc16is7xx_port *s = container_of(ws, struct sc16is7xx_port, poll_work.work);
> +
> +	/* Reuse standard IRQ handler. Interrupt ID is unused in this context. */
> +	sc16is7xx_irq(0, s);
> +
> +	/* Setup delay based on SC16IS7XX_POLL_PERIOD_MS */
> +	kthread_queue_delayed_work(&s->kworker, &s->poll_work,
> +				   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD_MS));
> +}
> +
>  static void sc16is7xx_tx_proc(struct kthread_work *ws)
>  {
>  	struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port);
> @@ -1149,6 +1164,7 @@ 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;
>  
> @@ -1211,6 +1227,10 @@ static int sc16is7xx_startup(struct uart_port *port)
>  	sc16is7xx_enable_ms(port);
>  	uart_port_unlock_irqrestore(port, flags);
>  
> +	if (s->polling)
> +		kthread_queue_delayed_work(&s->kworker, &s->poll_work,
> +					   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD_MS));
> +
>  	return 0;
>  }
>  
> @@ -1232,6 +1252,9 @@ static void sc16is7xx_shutdown(struct uart_port *port)
>  
>  	sc16is7xx_power(port, 0);
>  
> +	if (s->polling)
> +		kthread_cancel_delayed_work_sync(&s->poll_work);
> +
>  	kthread_flush_worker(&s->kworker);
>  }
>  
> @@ -1537,6 +1560,12 @@ 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);

You are still missing a blank line here to better separate logical
blocks (polling is not related to clock-frequency).

> +	s->polling = !device_property_present(dev, "interrupts");
> +	if (s->polling) {
> +		dev_dbg(dev,
> +			"No interrupt pin definition, falling back to polling mode\n");
> +		irq = 0;
> +	}
>  
>  	s->clk = devm_clk_get_optional(dev, NULL);
>  	if (IS_ERR(s->clk))
> @@ -1665,6 +1694,12 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
>  		goto out_ports;
>  #endif
>  
> +	if (s->polling) {
> +		/* Initialize kernel thread for polling */
> +		kthread_init_delayed_work(&s->poll_work, sc16is7xx_poll_proc);
> +		return 0;
> +	}
> +
>  	/*
>  	 * Setup interrupt. We first try to acquire the IRQ line as level IRQ.
>  	 * If that succeeds, we can allow sharing the interrupt as well.
> @@ -1724,6 +1759,9 @@ void sc16is7xx_remove(struct device *dev)
>  		sc16is7xx_power(&s->p[i].port, 0);
>  	}
>  
> +	if (s->polling)
> +		kthread_cancel_delayed_work_sync(&s->poll_work);
> +
>  	kthread_flush_worker(&s->kworker);
>  	kthread_stop(s->kworker_task);
>  
> -- 
> 2.47.1
> 
> 
> 


-- 
Hugo Villeneuve