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Date: Tue, 14 Jul 2020 09:13:55 +0200
From: Johan Hovold <johan@...nel.org>
To: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
Cc: Jacek Anaszewski <jacek.anaszewski@...il.com>,
Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>, kernel@...gutronix.de,
linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-leds@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v7 3/3] leds: trigger: implement a tty trigger
On Tue, Jul 07, 2020 at 06:59:58PM +0200, Uwe Kleine-König wrote:
> Usage is as follows:
>
> myled=ledname
> tty=ttyS0
>
> echo tty > /sys/class/leds/$myled/trigger
> echo $tty > /sys/class/leds/$myled/ttyname
>
> . When this new trigger is active it periodically checks the tty's
> statistics and when it changed since the last check the led is flashed
> once.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
> .../ABI/testing/sysfs-class-led-trigger-tty | 6 +
> drivers/leds/trigger/Kconfig | 7 +
> drivers/leds/trigger/Makefile | 1 +
> drivers/leds/trigger/ledtrig-tty.c | 192 ++++++++++++++++++
> 4 files changed, 206 insertions(+)
> create mode 100644 Documentation/ABI/testing/sysfs-class-led-trigger-tty
> create mode 100644 drivers/leds/trigger/ledtrig-tty.c
>
> diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-tty b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
> new file mode 100644
> index 000000000000..5c53ce3ede36
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
> @@ -0,0 +1,6 @@
> +What: /sys/class/leds/<led>/ttyname
> +Date: Jul 2020
> +KernelVersion: 5.8
> +Contact: linux-leds@...r.kernel.org
> +Description:
> + Specifies the tty device name of the triggering tty
> diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
> index ce9429ca6dde..40ff08c93f56 100644
> --- a/drivers/leds/trigger/Kconfig
> +++ b/drivers/leds/trigger/Kconfig
> @@ -144,4 +144,11 @@ config LEDS_TRIGGER_AUDIO
> the audio mute and mic-mute changes.
> If unsure, say N
>
> +config LEDS_TRIGGER_TTY
> + tristate "LED Trigger for TTY devices"
> + depends on TTY
> + help
> + This allows LEDs to be controlled by activity on ttys which includes
> + serial devices like /dev/ttyS0.
> +
> endif # LEDS_TRIGGERS
> diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
> index 733a83e2a718..25c4db97cdd4 100644
> --- a/drivers/leds/trigger/Makefile
> +++ b/drivers/leds/trigger/Makefile
> @@ -15,3 +15,4 @@ obj-$(CONFIG_LEDS_TRIGGER_PANIC) += ledtrig-panic.o
> obj-$(CONFIG_LEDS_TRIGGER_NETDEV) += ledtrig-netdev.o
> obj-$(CONFIG_LEDS_TRIGGER_PATTERN) += ledtrig-pattern.o
> obj-$(CONFIG_LEDS_TRIGGER_AUDIO) += ledtrig-audio.o
> +obj-$(CONFIG_LEDS_TRIGGER_TTY) += ledtrig-tty.o
> diff --git a/drivers/leds/trigger/ledtrig-tty.c b/drivers/leds/trigger/ledtrig-tty.c
> new file mode 100644
> index 000000000000..e44e2202fa34
> --- /dev/null
> +++ b/drivers/leds/trigger/ledtrig-tty.c
> @@ -0,0 +1,192 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/delay.h>
> +#include <linux/leds.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +#include <uapi/linux/serial.h>
> +
> +struct ledtrig_tty_data {
> + struct led_classdev *led_cdev;
> + struct delayed_work dwork;
> + struct mutex mutex;
> + const char *ttyname;
> + struct tty_struct *tty;
> + int rx, tx;
> +};
> +
> +static void ledtrig_tty_halt(struct ledtrig_tty_data *trigger_data)
> +{
> + cancel_delayed_work_sync(&trigger_data->dwork);
> +}
> +static ssize_t ttyname_store(struct device *dev,
> + struct device_attribute *attr, const char *buf,
> + size_t size)
> +{
> + struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
> + char *ttyname;
> + ssize_t ret = size;
> +
> + ledtrig_tty_halt(trigger_data);
> +
> + mutex_lock(&trigger_data->mutex);
> +
> + if (size > 0 && buf[size - 1] == '\n')
> + size -= 1;
> +
> + if (size) {
> + ttyname = kmemdup_nul(buf, size, GFP_KERNEL);
> + if (!ttyname) {
> + ret = -ENOMEM;
> + goto out_unlock;
> + }
> + } else {
> + ttyname = NULL;
> + }
> +
> + kfree(trigger_data->ttyname);
> + tty_kref_put(trigger_data->tty);
> + trigger_data->tty = NULL;
> +
> + trigger_data->ttyname = ttyname;
> +
> +out_unlock:
> + mutex_unlock(&trigger_data->mutex);
> +
> + if (ttyname)
> + ledtrig_tty_restart(trigger_data);
> +
> + return ret;
> +}
> +static DEVICE_ATTR_RW(ttyname);
> +
> +static void ledtrig_tty_work(struct work_struct *work)
> +{
> + struct ledtrig_tty_data *trigger_data =
> + container_of(work, struct ledtrig_tty_data, dwork.work);
> + struct serial_icounter_struct icount;
> + int ret;
> + bool firstrun = false;
> +
> + mutex_lock(&trigger_data->mutex);
> +
> + BUG_ON(!trigger_data->ttyname);
> +
> + /* try to get the tty corresponding to $ttyname */
> + if (!trigger_data->tty) {
> + dev_t devno;
> + struct tty_struct *tty;
> + int ret;
> +
> + firstrun = true;
> +
> + ret = tty_dev_name_to_number(trigger_data->ttyname, &devno);
> + if (ret < 0)
> + /*
> + * A device with this name might appear later, so keep
> + * retrying.
> + */
> + goto out;
> +
> + tty = tty_kopen_shared(devno);
> + if (IS_ERR(tty) || !tty)
> + /* What to do? retry or abort */
> + goto out;
> +
> + trigger_data->tty = tty;
> + }
> +
> + ret = tty_get_icount(trigger_data->tty, &icount);
> + if (ret)
> + return;
> +
> + while (firstrun ||
> + icount.rx != trigger_data->rx ||
> + icount.tx != trigger_data->tx) {
> +
> + led_set_brightness(trigger_data->led_cdev, LED_ON);
> +
> + msleep(100);
> +
> + led_set_brightness(trigger_data->led_cdev, LED_OFF);
> +
> + trigger_data->rx = icount.rx;
> + trigger_data->tx = icount.tx;
> + firstrun = false;
> +
> + ret = tty_get_icount(trigger_data->tty, &icount);
> + if (ret)
> + return;
> + }
Haven't looked at the latest proposal in detail, but this looks broken
as you can potentially loop indefinitely in a worker thread, and with no
way to stop the trigger (delayed work).
> +
> +out:
> + mutex_unlock(&trigger_data->mutex);
> + schedule_delayed_work(&trigger_data->dwork, msecs_to_jiffies(100));
> +}
Johan
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