Date:	Thu, 10 Mar 2016 10:23:49 +0100
From:	Oliver Neukum <oneukum@...e.com>
To:	Alexey Klimov <klimov.linux@...il.com>
Cc:	linux-watchdog@...r.kernel.org, yury.norov@...il.com,
	wim@...ana.be, linux@...ck-us.net, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] watchdog: add driver for StreamLabs USB watchdog device

On Thu, 2016-03-10 at 02:29 +0000, Alexey Klimov wrote:
> This patch creates new driver that supports StreamLabs usb watchdog
> device. This device plugs into 9-pin usb header and connects to
> reset pin and reset button on common PC.

Hi,

a few remarks.

	Regards
		Oliver

> 
> USB commands used to communicate with device were reverse
> engineered using usbmon.
> 
> Signed-off-by: Alexey Klimov <klimov.linux@...il.com>
> ---
>  drivers/watchdog/Kconfig          |  15 ++
>  drivers/watchdog/Makefile         |   1 +
>  drivers/watchdog/streamlabs_wdt.c | 370 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 386 insertions(+)
>  create mode 100644 drivers/watchdog/streamlabs_wdt.c
> 
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index 80825a7..95d8f72 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -1705,4 +1705,19 @@ config USBPCWATCHDOG
>  
>  	  Most people will say N.
>  
> +config USB_STREAMLABS_WATCHDOG
> +	tristate "StreamLabs USB watchdog driver"
> +	depends on USB
> +	---help---
> +	  This is the driver for the USB Watchdog dongle from StreamLabs.
> +	  If you correctly connect reset pins to motherboard Reset pin and
> +	  to Reset button then this device will simply watch your kernel to make
> +	  sure it doesn't freeze, and if it does, it reboots your computer
> +	  after a certain amount of time.
> +
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called streamlabs_wdt.
> +
> +	  Most people will say N. Say yes or M if you want to use such usb device.
>  endif # WATCHDOG
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index f6a6a38..d54fd31 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -25,6 +25,7 @@ obj-$(CONFIG_WDTPCI) += wdt_pci.o
>  
>  # USB-based Watchdog Cards
>  obj-$(CONFIG_USBPCWATCHDOG) += pcwd_usb.o
> +obj-$(CONFIG_USB_STREAMLABS_WATCHDOG) += streamlabs_wdt.o
>  
>  # ALPHA Architecture
>  
> diff --git a/drivers/watchdog/streamlabs_wdt.c b/drivers/watchdog/streamlabs_wdt.c
> new file mode 100644
> index 0000000..031dbc35
> --- /dev/null
> +++ b/drivers/watchdog/streamlabs_wdt.c
> @@ -0,0 +1,370 @@
> +/*
> + * StreamLabs USB Watchdog driver
> + *
> + * Copyright (c) 2016 Alexey Klimov <klimov.linux@...il.com>
> + *
> + * This program is free software; you may redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +#include <linux/usb.h>
> +#include <linux/watchdog.h>
> +
> +/*
> + * USB Watchdog device from Streamlabs
> + * http://www.stream-labs.com/products/devices/watchdog/
> + *
> + * USB commands have been reverse engineered using usbmon.
> + */
> +
> +#define DRIVER_AUTHOR "Alexey Klimov <klimov.linux@...il.com>"
> +#define DRIVER_DESC "StreamLabs USB watchdog driver"
> +#define DRIVER_NAME "usb_streamlabs_wdt"
> +
> +MODULE_AUTHOR(DRIVER_AUTHOR);
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_LICENSE("GPL");
> +
> +#define USB_STREAMLABS_WATCHDOG_VENDOR	0x13c0
> +#define USB_STREAMLABS_WATCHDOG_PRODUCT	0x0011
> +
> +/* one buffer is used for communication, however transmitted message is only
> + * 32 bytes long */
> +#define BUFFER_TRANSFER_LENGTH	32
> +#define BUFFER_LENGTH		64
> +#define USB_TIMEOUT		350
> +
> +#define STREAMLABS_CMD_START	0
> +#define STREAMLABS_CMD_STOP	1
> +
> +#define STREAMLABS_WDT_MIN_TIMEOUT	1
> +#define STREAMLABS_WDT_MAX_TIMEOUT	46
> +
> +struct streamlabs_wdt {
> +	struct watchdog_device wdt_dev;
> +	struct usb_device *usbdev;

You can always deduce the device from the interface. There's
no need to store it.

> +	struct usb_interface *intf;
> +
> +	struct kref kref;
> +	struct mutex lock;
> +	u8 *buffer;
> +};
> +
> +static bool nowayout = WATCHDOG_NOWAYOUT;
> +
> +static int usb_streamlabs_wdt_validate_response(u8 *buf)
> +{
> +	/* If watchdog device understood the command it will acknowledge
> +	 * with values 1,2,3,4 at indexes 10, 11, 12, 13 in response message.
> +	 */
> +	if (buf[10] != 1 || buf[11] != 2 || buf[12] != 3 || buf[13] != 4)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int usb_streamlabs_wdt_command(struct watchdog_device *wdt_dev, int cmd)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = watchdog_get_drvdata(wdt_dev);
> +	int retval;
> +	int size;
> +	unsigned long timeout_msec;
> +	int retry_counter = 10;		/* how many times to re-send stop cmd */
> +
> +	mutex_lock(&streamlabs_wdt->lock);
> +
> +	timeout_msec = wdt_dev->timeout * MSEC_PER_SEC;
> +
> +	/* Prepare message that will be sent to device.
> +	 * This buffer is allocated by kzalloc(). Only initialize required
> +	 * fields.
> +	 */
> +	if (cmd == STREAMLABS_CMD_START) {
> +		streamlabs_wdt->buffer[0] = 0xcc;
> +		streamlabs_wdt->buffer[1] = 0xaa;
> +	} else {	/* assume stop command if it's not start */
> +		streamlabs_wdt->buffer[0] = 0xff;
> +		streamlabs_wdt->buffer[1] = 0xbb;
> +	}
> +
> +	streamlabs_wdt->buffer[3] = 0x80;
> +
> +	streamlabs_wdt->buffer[6] = (timeout_msec & 0xff) << 8;
> +	streamlabs_wdt->buffer[7] = (timeout_msec & 0xff00) >> 8;

We have macros for such conversions. Please use them.

> +retry:

Why rewrite only a part of the buffer this way?

> +	streamlabs_wdt->buffer[10] = 0x00;
> +	streamlabs_wdt->buffer[11] = 0x00;
> +	streamlabs_wdt->buffer[12] = 0x00;
> +	streamlabs_wdt->buffer[13] = 0x00;
> +
> +	/* send command to watchdog */
> +	retval = usb_interrupt_msg(streamlabs_wdt->usbdev,
> +				usb_sndintpipe(streamlabs_wdt->usbdev, 0x02),
> +				streamlabs_wdt->buffer, BUFFER_TRANSFER_LENGTH,
> +				&size, USB_TIMEOUT);
> +
> +	if (retval || size != BUFFER_TRANSFER_LENGTH) {
> +		dev_err(&streamlabs_wdt->intf->dev,
> +			"error %i when submitting interrupt msg\n", retval);
> +		retval = -EIO;
> +		goto out;
> +	}
> +
> +	/* and read response from watchdog */
> +	retval = usb_interrupt_msg(streamlabs_wdt->usbdev,
> +				usb_rcvintpipe(streamlabs_wdt->usbdev, 0x81),
> +				streamlabs_wdt->buffer, BUFFER_LENGTH,
> +				&size, USB_TIMEOUT);
> +
> +	if (retval || size != BUFFER_LENGTH) {
> +		dev_err(&streamlabs_wdt->intf->dev,
> +			"error %i when receiving interrupt msg\n", retval);
> +		retval = -EIO;
> +		goto out;
> +	}
> +
> +	/* check if watchdog actually acked/recognized command */
> +	retval = usb_streamlabs_wdt_validate_response(streamlabs_wdt->buffer);
> +	if (retval) {
> +		dev_err(&streamlabs_wdt->intf->dev,
> +					"watchdog didn't ACK command!\n");
> +		goto out;
> +	}
> +
> +	/* Transition from enabled to disabled state in this device
> +	 * doesn't happen immediately. Usually, 2 or 3 (sometimes even 4) stop
> +	 * commands should be sent until watchdog answers 'I'm stopped!'.
> +	 * Retry stop command if watchdog fails to answer correctly
> +	 * about its state. After 10 attempts, report error and return -EIO.
> +	 */
> +	if (cmd == STREAMLABS_CMD_STOP) {
> +		if (--retry_counter <= 0) {
> +			dev_err(&streamlabs_wdt->intf->dev,
> +				"failed to stop watchdog after 9 attempts!\n");
> +			retval = -EIO;
> +			goto out;
> +		}
> +		/*
> +		 * Check if watchdog actually changed state to disabled.
> +		 * If watchdog is still enabled then reset message and retry
> +		 * stop command.
> +		 */
> +		if (streamlabs_wdt->buffer[0] != 0xff ||
> +					streamlabs_wdt->buffer[1] != 0xbb) {
> +			streamlabs_wdt->buffer[0] = 0xff;
> +			streamlabs_wdt->buffer[1] = 0xbb;
> +			goto retry;
> +		}
> +	}
> +
> +out:
> +	mutex_unlock(&streamlabs_wdt->lock);
> +	return retval;
> +}
> +
> +static int usb_streamlabs_wdt_start(struct watchdog_device *wdt_dev)
> +{
> +	return usb_streamlabs_wdt_command(wdt_dev, STREAMLABS_CMD_START);
> +}
> +
> +static int usb_streamlabs_wdt_stop(struct watchdog_device *wdt_dev)
> +{
> +	return usb_streamlabs_wdt_command(wdt_dev, STREAMLABS_CMD_STOP);
> +}
> +
> +static int usb_streamlabs_wdt_settimeout(struct watchdog_device *wdt_dev,
> +				unsigned int timeout)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = watchdog_get_drvdata(wdt_dev);
> +
> +	mutex_lock(&streamlabs_wdt->lock);
> +	wdt_dev->timeout = timeout;
> +	mutex_unlock(&streamlabs_wdt->lock);
> +
> +	return 0;
> +}
> +
> +static void usb_streamlabs_wdt_release_resources(struct kref *kref)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt =
> +			container_of(kref, struct streamlabs_wdt, kref);
> +
> +	mutex_destroy(&streamlabs_wdt->lock);
> +	kfree(streamlabs_wdt->buffer);
> +	kfree(streamlabs_wdt);
> +}
> +
> +static void usb_streamlabs_wdt_ref(struct watchdog_device *wdt_dev)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = watchdog_get_drvdata(wdt_dev);
> +
> +	kref_get(&streamlabs_wdt->kref);
> +}
> +
> +static void usb_streamlabs_wdt_unref(struct watchdog_device *wdt_dev)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = watchdog_get_drvdata(wdt_dev);
> +
> +	kref_put(&streamlabs_wdt->kref, usb_streamlabs_wdt_release_resources);
> +}
> +
> +static const struct watchdog_info streamlabs_wdt_ident = {
> +	.options	= (WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING),
> +	.identity	= DRIVER_NAME,
> +};
> +
> +static struct watchdog_ops usb_streamlabs_wdt_ops = {
> +	.owner	= THIS_MODULE,
> +	.start	= usb_streamlabs_wdt_start,
> +	.stop	= usb_streamlabs_wdt_stop,
> +	.set_timeout	= usb_streamlabs_wdt_settimeout,
> +	.ref	= usb_streamlabs_wdt_ref,
> +	.unref	= usb_streamlabs_wdt_unref,
> +};
> +
> +static int usb_streamlabs_wdt_probe(struct usb_interface *intf,
> +			const struct usb_device_id *id)
> +{
> +	struct usb_device *dev = interface_to_usbdev(intf);
> +	struct streamlabs_wdt *streamlabs_wdt;
> +	int retval;
> +
> +	/* USB IDs of this device appear to be weird/unregistered. Hence, do
> +	 * an additional check on product and manufacturer.
> +	 * If there is similar device in the field with same values then
> +	 * there is stop command in probe() below that checks if the device
> +	 * behaves as a watchdog. */
> +	if (dev->product && dev->manufacturer &&
> +		(strncmp(dev->product, "USBkit", 6) != 0
> +		|| strncmp(dev->manufacturer, "STREAM LABS", 11) != 0))
> +		return -ENODEV;
> +
> +	streamlabs_wdt = kmalloc(sizeof(struct streamlabs_wdt), GFP_KERNEL);
> +	if (!streamlabs_wdt) {
> +		dev_err(&intf->dev, "kmalloc failed\n");
> +		return -ENOMEM;
> +	}
> +
> +	streamlabs_wdt->buffer = kzalloc(BUFFER_LENGTH, GFP_KERNEL);
> +	if (!streamlabs_wdt->buffer) {
> +		dev_err(&intf->dev, "kzalloc for watchdog->buffer failed\n");
> +		retval = -ENOMEM;
> +		goto err_nobuf;
> +	}
> +
> +	mutex_init(&streamlabs_wdt->lock);
> +
> +	streamlabs_wdt->wdt_dev.info = &streamlabs_wdt_ident;
> +	streamlabs_wdt->wdt_dev.ops = &usb_streamlabs_wdt_ops;
> +	streamlabs_wdt->wdt_dev.timeout = STREAMLABS_WDT_MAX_TIMEOUT;
> +	streamlabs_wdt->wdt_dev.max_timeout = STREAMLABS_WDT_MAX_TIMEOUT;
> +	streamlabs_wdt->wdt_dev.min_timeout = STREAMLABS_WDT_MIN_TIMEOUT;
> +	streamlabs_wdt->wdt_dev.parent = &intf->dev;
> +
> +	streamlabs_wdt->usbdev = interface_to_usbdev(intf);
> +	streamlabs_wdt->intf = intf;
> +	usb_set_intfdata(intf, &streamlabs_wdt->wdt_dev);
> +	watchdog_set_drvdata(&streamlabs_wdt->wdt_dev, streamlabs_wdt);
> +
> +	watchdog_init_timeout(&streamlabs_wdt->wdt_dev,
> +				streamlabs_wdt->wdt_dev.timeout, &intf->dev);
> +	watchdog_set_nowayout(&streamlabs_wdt->wdt_dev, nowayout);
> +
> +	kref_init(&streamlabs_wdt->kref);
> +
> +	retval = usb_streamlabs_wdt_stop(&streamlabs_wdt->wdt_dev);
> +	if (retval)
> +		goto err_wdt_buf;
> +
> +	retval = watchdog_register_device(&streamlabs_wdt->wdt_dev);
> +	if (retval) {
> +		dev_err(&intf->dev, "failed to register watchdog device\n");
> +		goto err_wdt_buf;
> +	}
> +
> +	dev_info(&intf->dev, "StreamLabs USB watchdog loaded.\n");
> +
> +	return 0;
> +
> +err_wdt_buf:
> +	mutex_destroy(&streamlabs_wdt->lock);
> +	kfree(streamlabs_wdt->buffer);
> +
> +err_nobuf:
> +	kfree(streamlabs_wdt);
> +	return retval;
> +}
> +
> +
> +
> +static int usb_streamlabs_wdt_suspend(struct usb_interface *intf,
> +					pm_message_t message)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = usb_get_intfdata(intf);
> +
> +	if (watchdog_active(&streamlabs_wdt->wdt_dev))
> +		usb_streamlabs_wdt_command(&streamlabs_wdt->wdt_dev,
> +							STREAMLABS_CMD_STOP);
> +
> +	return 0;
> +}

If the result of a failure would be a spurious reset, you cannot drop
errors.

> +
> +static int usb_streamlabs_wdt_resume(struct usb_interface *intf)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = usb_get_intfdata(intf);
> +
> +	if (watchdog_active(&streamlabs_wdt->wdt_dev))
> +		return usb_streamlabs_wdt_command(&streamlabs_wdt->wdt_dev,
> +							STREAMLABS_CMD_START);
> +
> +	return 0;
> +}
> +
> +static void usb_streamlabs_wdt_disconnect(struct usb_interface *intf)
> +{
> +	struct streamlabs_wdt *streamlabs_wdt = usb_get_intfdata(intf);
> +
> +	/* First, stop sending USB messages to device. */

That is problematic. A disconnect can be triggered by removal of
the hardware or in software through sysfs. In the latter case a
running device without a driver would trigger a reset, wouldn't it?
So I think for watchdog devices you need to go to an inactive
state in disconnect().

> +	mutex_lock(&streamlabs_wdt->lock);
> +	usb_set_intfdata(intf, NULL);
> +	streamlabs_wdt->usbdev = NULL;
> +	mutex_unlock(&streamlabs_wdt->lock);
> +
> +	/* after commincation with device has stopped we can
> +	 * unregister watchdog device. unref callback will clear the rest on
> +	 * release of device if it was opened.
> +	 */
> +	watchdog_unregister_device(&streamlabs_wdt->wdt_dev);
> +	kref_put(&streamlabs_wdt->kref, usb_streamlabs_wdt_release_resources);
> +}
> +
> +static struct usb_device_id usb_streamlabs_wdt_device_table[] = {
> +	{ USB_DEVICE(USB_STREAMLABS_WATCHDOG_VENDOR, USB_STREAMLABS_WATCHDOG_PRODUCT) },
> +	{ }	/* Terminating entry */
> +};
> +
> +MODULE_DEVICE_TABLE(usb, usb_streamlabs_wdt_device_table);
> +
> +static struct usb_driver usb_streamlabs_wdt_driver = {
> +	.name		= DRIVER_NAME,
> +	.probe		= usb_streamlabs_wdt_probe,
> +	.disconnect	= usb_streamlabs_wdt_disconnect,
> +	.suspend	= usb_streamlabs_wdt_suspend,
> +	.resume		= usb_streamlabs_wdt_resume,
> +	.reset_resume	= usb_streamlabs_wdt_resume,
> +	.id_table	= usb_streamlabs_wdt_device_table,
> +};
> +
> +module_usb_driver(usb_streamlabs_wdt_driver);

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