Re: [PATCH] tty: implement a rx led trigger

Uwe Kleine-König
2018-05-03T11:52:27Z

On Thu, May 03, 2018 at 12:10:47PM +0200, Pavel Machek wrote:
> Hi!
>
> > The trigger fires when data is pushed to the ldisc. This is a bit later
> > than the actual receiving of data but has the nice benefit that it
> > doesn't need adaption for each driver and isn't in the hot path.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
>
> Well, why not, but there certainly should be config option? Because I
> really don't see many people wanting to use this trigger.

Yeah, can be done. I'll implement this for v2.

> > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> > index c996b6859c5e..4d364b77b1a7 100644
> > --- a/drivers/tty/tty_buffer.c
> > +++ b/drivers/tty/tty_buffer.c
> > @@ -17,6 +17,7 @@
> > #include <linux/delay.h>
> > #include <linux/module.h>
> > #include <linux/ratelimit.h>
> > +#include <linux/leds.h>
> >
> >
> > #define MIN_TTYB_SIZE 256
> > @@ -499,6 +500,7 @@ static void flush_to_ldisc(struct work_struct *work)
> > struct tty_buffer *head = buf->head;
> > struct tty_buffer *next;
> > int count;
> > + unsigned long delay = 50 /* ms */;
> >
> > /* Ldisc or user is trying to gain exclusive access */
> > if (atomic_read(&buf->priority))
> > @@ -521,6 +523,8 @@ static void flush_to_ldisc(struct work_struct *work)
> > continue;
> > }
> >
> > + led_trigger_blink_oneshot(port->led_trigger_rx, &delay, &delay, 0);
> > +
> > count = receive_buf(port, head, count);
> > if (!count)
> > break;
> > diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
> > index 25d736880013..51b78a585417 100644
> > --- a/drivers/tty/tty_port.c
> > +++ b/drivers/tty/tty_port.c
> > @@ -16,6 +16,7 @@
> > #include <linux/wait.h>
> > #include <linux/bitops.h>
> > #include <linux/delay.h>
> > +#include <linux/leds.h>
> > #include <linux/module.h>
> > #include <linux/serdev.h>
> >
> > @@ -157,6 +158,18 @@ struct device *tty_port_register_device_attr_serdev(struct tty_port *port,
> >
> > tty_port_link_device(port, driver, index);
> >
> > + port->led_trigger_rx_name = kasprintf(GFP_KERNEL, "%s%d-rx",
> > + driver->name, index);
> > + if (!port->led_trigger_rx_name) {
> > + pr_err("Failed to allocate trigger name for %s%d\n",
> > + driver->name, index);
> > + goto skip_trigger;
> > + }
> > +
> > + led_trigger_register_simple(port->led_trigger_rx_name,
> > + &port->led_trigger_rx);
> > +
> > +skip_trigger:
> > dev = serdev_tty_port_register(port, device, driver, index);
> > if (PTR_ERR(dev) != -ENODEV) {
> > /* Skip creating cdev if we registered a serdev device */
> > @@ -206,6 +219,9 @@ void tty_port_unregister_device(struct tty_port *port,
> > if (ret == 0)
> > return;
> >
> > + led_trigger_unregister_simple(port->led_trigger_rx);
>
> Is it ok to unregister if it was not registered in the first place?

led_trigger_unregister_simple() looks as follows:

if (trig)
led_trigger_unregister(trig);
kfree(trig);

So yes, it does the right thing when it wasn't registered. Assuming it
is NULL then, which doesn't seem to be guaranteed. Probably I'd need

port->led_trigger_rx = NULL

if kasprintf failed.

Best regards
Uwe

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