Subject: [PATCH 1/4] serial: core: Add LED trigger support

From: [email-masked] (Mathieu Poirier)
Date: Wed, 23 Nov 2016 10:13:02 -0700

On Wed, Nov 23, 2016 at 11:01:03AM +0100, Sascha Hauer wrote:
> With this patch the serial core provides LED triggers for RX and TX.
> 
> As the serial core layer does not know when the hardware actually sends
> or receives characters, this needs help from the UART drivers. The
> LED triggers are registered in uart_add_led_triggers() called from
> the UART drivers which want to support LED triggers. All the driver
> has to do then is to call uart_led_trigger_[tx|rx] to indicate
> activite.

Hello Sascha,

> 
> Signed-off-by: Sascha Hauer <[email-masked]>
> ---
>  drivers/tty/serial/serial_core.c | 73 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/serial_core.h      | 10 ++++++
>  2 files changed, 83 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index f2303f3..3e8afb7 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -34,6 +34,7 @@
>  #include <linux/serial_core.h>
>  #include <linux/delay.h>
>  #include <linux/mutex.h>
> +#include <linux/leds.h>
>  
>  #include <asm/irq.h>
>  #include <asm/uaccess.h>
> @@ -2703,6 +2704,77 @@ static const struct attribute_group tty_dev_attr_group = {
>  	.attrs = tty_dev_attrs,
>  	};
>  
> +void uart_led_trigger_tx(struct uart_port *uport)
> +{
> +	unsigned long delay = 50;
> +
> +	led_trigger_blink_oneshot(uport->led_trigger_tx, &delay, &delay, 0);
> +}
> +
> +void uart_led_trigger_rx(struct uart_port *uport)
> +{
> +	unsigned long delay = 50;
> +
> +	led_trigger_blink_oneshot(uport->led_trigger_rx, &delay, &delay, 0);

For both rx/tx the core constrains the delay_on/off along with the inversion.
Instead of adding the led_trigger_rx/tx and led_trigger_rx/tx_name to the 
struct uart_port, wouldn't it be better to add a new struct led_trigger that
would encapsulate those along wit the on/off delay and the inversion?

That way those values could be communicated to the core at registration time
instead of hard-coding things.
 
> +}
> +
> +/**
> + *	uart_add_led_triggers - register LED triggers for a UART
> + *	@drv: pointer to the uart low level driver structure for this port
> + *	@uport: uart port structure to use for this port.
> + *
> + *	Called by the driver to register LED triggers for a UART. It's the
> + *	drivers responsibility to call uart_led_trigger_rx/tx on received
> + *	and transmitted chars then.
> + */
> +int uart_add_led_triggers(struct uart_driver *drv, struct uart_port *uport)
> +{
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_LEDS_TRIGGERS))
> +		return 0;

Since this is a public interface, checking for valid led_trigger_tx/rx before
moving on with the rest of the initialisation is probably a good idea.

Thanks,
Mathieu

> +
> +	uport->led_trigger_tx_name = kasprintf(GFP_KERNEL, "%s%d-tx",
> +					       drv->dev_name, uport->line);
> +	uport->led_trigger_rx_name = kasprintf(GFP_KERNEL, "%s%d-rx",
> +					       drv->dev_name, uport->line);
> +	if (!uport->led_trigger_tx_name || !uport->led_trigger_rx_name) {
> +		ret = -ENOMEM;
> +		goto err_alloc;
> +	}
> +
> +	led_trigger_register_simple(uport->led_trigger_tx_name,
> +				    &uport->led_trigger_tx);
> +	led_trigger_register_simple(uport->led_trigger_rx_name,
> +				    &uport->led_trigger_rx);
> +
> +	return 0;
> +
> +err_alloc:
> +	kfree(uport->led_trigger_tx_name);
> +	kfree(uport->led_trigger_rx_name);
> +
> +	return ret;
> +}
> +
> +/**
> + *	uart_remove_led_triggers - remove LED triggers
> + *	@drv: pointer to the uart low level driver structure for this port
> + *	@uport: uart port structure to use for this port.
> + *
> + *	Remove LED triggers previously registered with uart_add_led_triggers
> + */
> +void uart_remove_led_triggers(struct uart_port *uport)
> +{
> +	if (uport->led_trigger_rx)
> +		led_trigger_unregister_simple(uport->led_trigger_rx);
> +	kfree(uport->led_trigger_rx_name);
> +
> +	if (uport->led_trigger_tx)
> +		led_trigger_unregister_simple(uport->led_trigger_tx);
> +	kfree(uport->led_trigger_tx_name);
> +}
> +
>  /**
>   *	uart_add_one_port - attach a driver-defined port structure
>   *	@drv: pointer to the uart low level driver structure for this port
> @@ -2872,6 +2944,7 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
>  	WARN_ON(atomic_dec_return(&state->refcount) < 0);
>  	wait_event(state->remove_wait, !atomic_read(&state->refcount));
>  	state->uart_port = NULL;
> +
>  	mutex_unlock(&port->mutex);
>  out:
>  	mutex_unlock(&port_mutex);
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 3442014..1b0a169 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -29,6 +29,7 @@
>  #include <linux/tty.h>
>  #include <linux/mutex.h>
>  #include <linux/sysrq.h>
> +#include <linux/leds.h>
>  #include <uapi/linux/serial_core.h>
>  
>  #ifdef CONFIG_SERIAL_CORE_CONSOLE
> @@ -249,6 +250,10 @@ struct uart_port {
>  	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
>  	struct serial_rs485     rs485;
>  	void			*private_data;		/* generic platform data pointer */
> +	struct led_trigger	*led_trigger_rx;
> +	char			*led_trigger_rx_name;
> +	struct led_trigger	*led_trigger_tx;
> +	char			*led_trigger_tx_name;
>  };
>  
>  static inline int serial_port_in(struct uart_port *up, int offset)
> @@ -392,6 +397,11 @@ void uart_console_write(struct uart_port *port, const char *s,
>  			unsigned int count,
>  			void (*putchar)(struct uart_port *, int));
>  
> +int uart_add_led_triggers(struct uart_driver *drv, struct uart_port *uport);
> +void uart_remove_led_triggers(struct uart_port *uport);
> +void uart_led_trigger_tx(struct uart_port *port);
> +void uart_led_trigger_rx(struct uart_port *port);
> +
>  /*
>   * Port/driver registration/removal
>   */
> -- 
> 2.10.2
>