[v5] hid-mcp2200: added driver for GPIOs of MCP2200

From: Johannes Roith <johannes@gnu-linux.rocks>

Added a gpiochip compatible driver to control the 8 GPIOs of
the MCP2200 by using the HID interface.

Using GPIOs with alternative functions (GP0<->SSPND, GP1<->USBCFG,
GP6<->RXLED, GP7<->TXLED) will reset the functions, if set (unset by
default).

The driver was tested while also using the UART of the chip. Setting
and reading the GPIOs has no effect on the UART communication. However,
a reset is triggered after the CONFIGURE command. If the GPIO Direction
is constantly changed, this will affect the communication at low baud
rates. This is a hardware problem of the MCP2200 and is not caused by
the driver.

Feedback from reviewers Christophe JAILLET <christophe.jaillet@wanadoo.fr>
and Andi Shyti <andi.shyti@kernel.org> was added.

Changelog:

- v1: added driver
- v2: added ProductID in hid-ids.h
- v3: added feedback from review and make patch compilable
- v4: added more feedback from second review, tested as module and
  builtin on x86 and arm64
- v5: adopted Kconfig to style guidelines, fixed mcp_set_direction

Signed-off-by: Johannes Roith <johannes@gnu-linux.rocks>
---
 drivers/hid/Kconfig       |  10 +
 drivers/hid/Makefile      |   1 +
 drivers/hid/hid-ids.h     |   1 +
 drivers/hid/hid-mcp2200.c | 419 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 431 insertions(+)
 create mode 100644 drivers/hid/hid-mcp2200.c

Commit message subject should probably start with "HID: mcp2200:"
rather than "hid-mcp2200:". This matches mcp2221.

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/hid/hid-mcp2221.c

On Fri, 18 Aug, 2023 12:48:52 +0200 <johannes@gnu-linux.rocks> wrote:
> From: Johannes Roith <johannes@gnu-linux.rocks>
>
> Added a gpiochip compatible driver to control the 8 GPIOs of
> the MCP2200 by using the HID interface.
>
> Using GPIOs with alternative functions (GP0<->SSPND, GP1<->USBCFG,
> GP6<->RXLED, GP7<->TXLED) will reset the functions, if set (unset by
> default).
>
> The driver was tested while also using the UART of the chip. Setting
> and reading the GPIOs has no effect on the UART communication. However,
> a reset is triggered after the CONFIGURE command. If the GPIO Direction
> is constantly changed, this will affect the communication at low baud
> rates. This is a hardware problem of the MCP2200 and is not caused by
> the driver.
>

The content below should not be in the commit message body but rather
git notes or a section in the patch that will not be applied.

> Feedback from reviewers Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> and Andi Shyti <andi.shyti@kernel.org> was added.
>
> Changelog:
>
> - v1: added driver
> - v2: added ProductID in hid-ids.h
> - v3: added feedback from review and make patch compilable
> - v4: added more feedback from second review, tested as module and
>   builtin on x86 and arm64
> - v5: adopted Kconfig to style guidelines, fixed mcp_set_direction

For your reference in case you find it helpful.

  * https://git-scm.com/docs/git-notes
  * https://git-scm.com/docs/git-format-patch#Documentation/git-format-patch.txt---notesltrefgt

>
> Signed-off-by: Johannes Roith <johannes@gnu-linux.rocks>
> ---
>  drivers/hid/Kconfig       |  10 +
>  drivers/hid/Makefile      |   1 +
>  drivers/hid/hid-ids.h     |   1 +
>  drivers/hid/hid-mcp2200.c | 419 ++++++++++++++++++++++++++++++++++++++
>  4 files changed, 431 insertions(+)
>  create mode 100644 drivers/hid/hid-mcp2200.c
>
> diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
> index e11c1c803676..efe01b473cc2 100644
> --- a/drivers/hid/Kconfig
> +++ b/drivers/hid/Kconfig
> @@ -1301,6 +1301,16 @@ config HID_MCP2221
>  	To compile this driver as a module, choose M here: the module
>  	will be called hid-mcp2221.ko.
>
> +config HID_MCP2200
> +	tristate "Microchip MCP2200 HID USB-to-GPIO bridge"
> +	depends on USB_HID
> +	imply GPIOLIB
> +	help
> +	  Provides GPIO functionality over USB-HID through MCP2200 device.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called hid-mcp2200.ko.
> +

Alphabetically, HID_MCP2200 should be before HID_MCP2221.

>  config HID_KUNIT_TEST
>  	tristate "KUnit tests for HID" if !KUNIT_ALL_TESTS
>  	depends on KUNIT
> diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
> index 7a9e160158f7..050f740304c4 100644
> --- a/drivers/hid/Makefile
> +++ b/drivers/hid/Makefile
> @@ -79,6 +79,7 @@ obj-$(CONFIG_HID_MACALLY)	+= hid-macally.o
>  obj-$(CONFIG_HID_MAGICMOUSE)	+= hid-magicmouse.o
>  obj-$(CONFIG_HID_MALTRON)	+= hid-maltron.o
>  obj-$(CONFIG_HID_MCP2221)	+= hid-mcp2221.o
> +obj-$(CONFIG_HID_MCP2200)	+= hid-mcp2200.o

Similar comment as previous here.

>  obj-$(CONFIG_HID_MAYFLASH)	+= hid-mf.o
>  obj-$(CONFIG_HID_MEGAWORLD_FF)	+= hid-megaworld.o
>  obj-$(CONFIG_HID_MICROSOFT)	+= hid-microsoft.o
> diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h
> index 8a310f8ff20f..4926ca41225b 100644
> --- a/drivers/hid/hid-ids.h
> +++ b/drivers/hid/hid-ids.h
> @@ -914,6 +914,7 @@
>  #define USB_DEVICE_ID_PICK16F1454_V2	0xf2f7
>  #define USB_DEVICE_ID_LUXAFOR		0xf372
>  #define USB_DEVICE_ID_MCP2221		0x00dd
> +#define USB_DEVICE_ID_MCP2200		0x00df

This file is sorted primarily by the define name rather than the device
id, so I would expect the define for mcp2200 to be before mcp2221 (even
though its device id would be after).

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/hid/hid-ids.h?id=aa9ea98cca3a56869df1dc6347f3e3bfe0c01f44#n449

>
>  #define USB_VENDOR_ID_MICROSOFT		0x045e
>  #define USB_DEVICE_ID_SIDEWINDER_GV	0x003b
> diff --git a/drivers/hid/hid-mcp2200.c b/drivers/hid/hid-mcp2200.c
> new file mode 100644
> index 000000000000..ed4483fa5bdf
> --- /dev/null
> +++ b/drivers/hid/hid-mcp2200.c
> @@ -0,0 +1,419 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * MCP2200 - Microchip USB to GPIO bridge
> + *
> + * Copyright (c) 2023, Johannes Roith <johannes@gnu-linux.rocks>
> + *
> + * Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/22228A.pdf
> + * App Note for HID: https://ww1.microchip.com/downloads/en/DeviceDoc/93066A.pdf
> + */
> +#include <linux/completion.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/hid.h>
> +#include <linux/hidraw.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include "hid-ids.h"
> +
> +/* Commands codes in a raw output report */
> +#define SET_CLEAR_OUTPUTS	0x08
> +#define CONFIGURE		0x10
> +#define READ_EE			0x20
> +#define WRITE_EE		0x40
> +#define READ_ALL		0x80
> +
> +/* MCP GPIO direction encoding */
> +enum MCP_IO_DIR {
> +	MCP2200_DIR_OUT = 0x00,
> +	MCP2200_DIR_IN  = 0x01,
> +};
> +
> +/* Altternative pin assignments */
> +#define TXLED		2
> +#define RXLED		3
> +#define USBCFG		6
> +#define SSPND		7
> +#define MCP_NGPIO	8
> +
> +/* CMD to set or clear a GPIO output */
> +struct mcp_set_clear_outputs {
> +	u8 cmd;
> +	u8 dummys1[10];
> +	u8 set_bmap;
> +	u8 clear_bmap;
> +	u8 dummys2[3];
> +} __packed;
> +
> +/* CMD to configure the IOs */
> +struct mcp_configure {
> +	u8 cmd;
> +	u8 dummys1[3];
> +	u8 io_bmap;
> +	u8 config_alt_pins;
> +	u8 io_default_val_bmap;
> +	u8 config_alt_options;
> +	u8 baud_h;
> +	u8 baud_l;
> +	u8 dummys2[6];
> +} __packed;
> +
> +/* CMD to read all parameters */
> +struct mcp_read_all {
> +	u8 cmd;
> +	u8 dummys[15];
> +} __packed;
> +
> +/* Response to the read all cmd */
> +struct mcp_read_all_resp {
> +	u8 cmd;
> +	u8 eep_addr;
> +	u8 dummy;
> +	u8 eep_val;
> +	u8 io_bmap;
> +	u8 config_alt_pins;
> +	u8 io_default_val_bmap;
> +	u8 config_alt_options;
> +	u8 baud_h;
> +	u8 baud_l;
> +	u8 io_port_val_bmap;
> +	u8 dummys[5];
> +} __packed;
> +
> +struct mcp2200 {
> +	struct hid_device *hdev;
> +	struct mutex lock;
> +	struct completion wait_in_report;
> +	u8 gpio_dir;
> +	u8 gpio_val;
> +	u8 gpio_inval;
> +	u8 baud_h;
> +	u8 baud_l;
> +	u8 config_alt_pins;
> +	u8 gpio_reset_val;
> +	u8 config_alt_options;
> +	int status;
> +	struct gpio_chip gc;
> +};
> +
> +/* this executes the READ_ALL cmd */
> +static int mcp_cmd_read_all(struct mcp2200 *mcp)
> +{
> +	struct mcp_read_all *read_all;
> +	int len, t;
> +
> +	reinit_completion(&mcp->wait_in_report);
> +	read_all = kzalloc(sizeof(struct mcp_read_all), GFP_KERNEL);
> +	if (!read_all)
> +		return -ENOMEM;

My personal recommendation is to just have a single DMA buffer allocated
for the mcp2200 instance rather than having to call the allocator and
release the memory per command.

Here is a reference.

  https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git/tree/drivers/hid/hid-nvidia-shield.c?id=1d7546042f8fdc4bc39ab91ec966203e2d64f8bd#n502

> +
> +	read_all->cmd = READ_ALL;
> +
> +	mutex_lock(&mcp->lock);
> +	len = hid_hw_output_report(mcp->hdev, (u8 *) read_all,
> +				   sizeof(struct mcp_read_all));
> +
> +	mutex_unlock(&mcp->lock);
> +	kfree(read_all);
> +
> +	if (len != sizeof(struct mcp_read_all))
> +		return -EINVAL;
> +
> +	t = wait_for_completion_timeout(&mcp->wait_in_report,
> +					msecs_to_jiffies(4000));
> +	if (!t)
> +		return -ETIMEDOUT;
> +
> +	/* return status, negative value if wrong response was received */
> +	return mcp->status;
> +}
> +
> +static void mcp_set_multiple(struct gpio_chip *gc, unsigned long *mask,
> +			     unsigned long *bits)
> +{
> +	struct mcp2200 *mcp = gpiochip_get_data(gc);
> +	u8 value;
> +	int status;
> +	struct mcp_set_clear_outputs *cmd;
> +
> +	cmd = kzalloc(sizeof(struct mcp_set_clear_outputs), GFP_KERNEL);
> +	if (!cmd)
> +		return;
> +
> +	mutex_lock(&mcp->lock);
> +
> +	value = mcp->gpio_val & ~*mask;
> +	value |= (*mask & *bits);
> +
> +	cmd->cmd = SET_CLEAR_OUTPUTS;
> +	cmd->set_bmap = value;
> +	cmd->clear_bmap = ~(value);
> +
> +	status = hid_hw_output_report(mcp->hdev, (u8 *) cmd,
> +		       sizeof(struct mcp_set_clear_outputs));
> +
> +	if (status == sizeof(struct mcp_set_clear_outputs))
> +		mcp->gpio_val = value;
> +
> +	mutex_unlock(&mcp->lock);
> +	kfree(cmd);
> +}
> +
> +static void mcp_set(struct gpio_chip *gc, unsigned int gpio_nr, int value)
> +{
> +	unsigned long mask = 1 << gpio_nr;
> +	unsigned long bmap_value = value << gpio_nr;
> +
> +	mcp_set_multiple(gc, &mask, &bmap_value);
> +}
> +
> +static int mcp_get_multiple(struct gpio_chip *gc, unsigned long *mask,
> +		unsigned long *bits)
> +{
> +	u32 val;
> +	struct mcp2200 *mcp = gpiochip_get_data(gc);
> +	int status;
> +
> +	status = mcp_cmd_read_all(mcp);
> +	if (status != 0)

Can be simplified as 'if (status)'.

> +		return status;
> +
> +	val = mcp->gpio_inval;
> +	*bits = (val & *mask);
> +	return 0;
> +}
> +
> +static int mcp_get(struct gpio_chip *gc, unsigned int gpio_nr)
> +{
> +	unsigned long mask = 0, bits = 0;

You do not need to zero init these variables? It's useful to avoid
initializing variables unnecessarily for compile time checking/static
analysis purposes.

> +
> +	mask = (1 << gpio_nr);
> +	mcp_get_multiple(gc, &mask, &bits);
> +	return bits > 0;
> +}
> +
> +static int mcp_get_direction(struct gpio_chip *gc, unsigned int gpio_nr)
> +{
> +	struct mcp2200 *mcp = gpiochip_get_data(gc);
> +
> +	return (mcp->gpio_dir & (MCP2200_DIR_IN << gpio_nr))
> +		? GPIO_LINE_DIRECTION_IN : GPIO_LINE_DIRECTION_OUT;
> +}
> +
> +static int mcp_set_direction(struct gpio_chip *gc, unsigned int gpio_nr,
> +			     enum MCP_IO_DIR io_direction)
> +{
> +	struct mcp2200 *mcp = gpiochip_get_data(gc);
> +	struct mcp_configure *conf;
> +	int status;
> +	/* after the configure cmd we will need to set the outputs again */
> +	unsigned long mask = ~(mcp->gpio_dir); /* only set outputs */
> +	unsigned long bits = mcp->gpio_val;
> +	/* Offsets of alternative pins in config_alt_pins, 0 is not used */
> +	u8 alt_pin_conf[8] = {SSPND, USBCFG, 0, 0, 0, 0, RXLED, TXLED};
> +	u8 config_alt_pins = mcp->config_alt_pins;
> +
> +	/* Read in the reset baudrate first, we need it later */
> +	status = mcp_cmd_read_all(mcp);
> +	if (status != 0)
> +		return status;
> +
> +	conf = kzalloc(sizeof(struct mcp_configure), GFP_KERNEL);
> +	if (!conf)
> +		return -ENOMEM;
> +
> +	mutex_lock(&mcp->lock);
> +
> +	/* configure will reset the chip! */
> +	conf->cmd = CONFIGURE;
> +	conf->io_bmap = (mcp->gpio_dir & ~(1 << gpio_nr))
> +		| (io_direction << gpio_nr);
> +	/* Don't overwrite the reset parameters */
> +	conf->baud_h = mcp->baud_h;
> +	conf->baud_l = mcp->baud_l;
> +	conf->config_alt_options = mcp->config_alt_options;
> +	conf->io_default_val_bmap = mcp->gpio_reset_val;
> +	/* Adjust alt. func if necessary */
> +	if (alt_pin_conf[gpio_nr])
> +		config_alt_pins &= ~(1 << alt_pin_conf[gpio_nr]);
> +	conf->config_alt_pins = config_alt_pins;
> +
> +	status = hid_hw_output_report(mcp->hdev, (u8 *) conf,
> +				      sizeof(struct mcp_set_clear_outputs));
> +
> +	if (status == sizeof(struct mcp_set_clear_outputs)) {
> +		mcp->gpio_dir = conf->io_bmap;
> +		mcp->config_alt_pins = config_alt_pins;
> +	} else {
> +		mutex_unlock(&mcp->lock);
> +		kfree(conf);
> +		return -EIO;
> +	}
> +
> +	mutex_unlock(&mcp->lock);
> +	kfree(conf);
> +
> +	/* Configure CMD will clear all IOs -> rewrite them */
> +	mcp_set_multiple(gc, &mask, &bits);
> +	return 0;
> +}
> +
> +static int mcp_direction_input(struct gpio_chip *gc, unsigned int gpio_nr)
> +{
> +	return mcp_set_direction(gc, gpio_nr, MCP2200_DIR_IN);
> +}
> +
> +static int mcp_direction_output(struct gpio_chip *gc, unsigned int gpio_nr,
> +				int value)
> +{
> +	int ret;
> +	unsigned long mask, bmap_value;
> +
> +	mask = 1 << gpio_nr;
> +	bmap_value = value << gpio_nr;
> +
> +	ret = mcp_set_direction(gc, gpio_nr, MCP2200_DIR_OUT);
> +	if (ret == 0)

'if (!ret)' can be used here.

> +		mcp_set_multiple(gc, &mask, &bmap_value);
> +	return ret;
> +}
> +
> +static const struct gpio_chip template_chip = {
> +	.label			= "mcp2200",
> +	.owner			= THIS_MODULE,
> +	.get_direction		= mcp_get_direction,
> +	.direction_input	= mcp_direction_input,
> +	.direction_output	= mcp_direction_output,
> +	.set			= mcp_set,
> +	.set_multiple		= mcp_set_multiple,
> +	.get			= mcp_get,
> +	.get_multiple		= mcp_get_multiple,
> +	.base			= -1,
> +	.ngpio			= MCP_NGPIO,
> +	.can_sleep		= true,
> +};
> +
> +/*
> + * MCP2200 uses interrupt endpoint for input reports. This function
> + * is called by HID layer when it receives i/p report from mcp2200,
> + * which is actually a response to the previously sent command.
> + */
> +static int mcp2200_raw_event(struct hid_device *hdev, struct hid_report *report,
> +		u8 *data, int size)
> +{
> +	struct mcp2200 *mcp = hid_get_drvdata(hdev);
> +	struct mcp_read_all_resp *all_resp;
> +
> +	switch (data[0]) {
> +	case READ_ALL:
> +		all_resp = (struct mcp_read_all_resp *) data;
> +		mcp->status = 0;
> +		mcp->gpio_inval = all_resp->io_port_val_bmap;
> +		mcp->baud_h = all_resp->baud_h;
> +		mcp->baud_l = all_resp->baud_l;
> +		mcp->gpio_reset_val = all_resp->io_default_val_bmap;
> +		mcp->config_alt_pins = all_resp->config_alt_pins;
> +		mcp->config_alt_options = all_resp->config_alt_options;
> +		break;
> +	default:
> +		mcp->status = -EIO;
> +		break;
> +	}
> +
> +	complete(&mcp->wait_in_report);
> +	return 1;

While this is not problematic today, I think it would be better to
return 0 here rather than 1.

> +}
> +
> +static void mcp2200_hid_unregister(void *ptr)
> +{
> +	struct hid_device *hdev = ptr;
> +
> +	hid_hw_close(hdev);
> +	hid_hw_stop(hdev);
> +}
> +
> +static int mcp2200_probe(struct hid_device *hdev, const struct hid_device_id *id)
> +{
> +	int ret;
> +	struct mcp2200 *mcp;
> +
> +	mcp = devm_kzalloc(&hdev->dev, sizeof(*mcp), GFP_KERNEL);
> +	if (!mcp)
> +		return -ENOMEM;
> +
> +	ret = hid_parse(hdev);
> +	if (ret) {
> +		hid_err(hdev, "can't parse reports\n");
> +		return ret;
> +	}
> +
> +	/*
> +	 * This driver uses the .raw_event callback and therefore does not need any
> +	 * HID_CONNECT_xxx flags.
> +	 */
> +	ret = hid_hw_start(hdev, 0);
> +	if (ret) {
> +		hid_err(hdev, "can't start hardware\n");
> +		return ret;
> +	}
> +
> +	hid_info(hdev, "USB HID v%x.%02x Device [%s] on %s\n", hdev->version >> 8,
> +			hdev->version & 0xff, hdev->name, hdev->phys);
> +
> +	ret = hid_hw_open(hdev);
> +	if (ret) {

Need to call hid_hw_stop here since hid_hw_start succeeded.

> +		hid_err(hdev, "can't open device\n");
> +		return ret;
> +	}
> +
> +	mutex_init(&mcp->lock);
> +	init_completion(&mcp->wait_in_report);
> +	hid_set_drvdata(hdev, mcp);
> +	mcp->hdev = hdev;
> +
> +	ret = devm_add_action_or_reset(&hdev->dev, mcp2200_hid_unregister, hdev);
> +	if (ret)

You probably want to call mcp2200_hid_unregister here since the action
was not added?

> +		return ret;
> +
> +	mcp->gc = template_chip;
> +	mcp->gc.parent = &hdev->dev;
> +
> +	ret = devm_gpiochip_add_data(&hdev->dev, &mcp->gc, mcp);
> +	if (ret < 0) {
> +		hid_err(hdev, "Unable to register gpiochip\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void mcp2200_remove(struct hid_device *hdev)
> +{
> +	(void) hdev;
> +	/*
> +	 * With no remove function you sometimes get a segmentation fault when
> +	 * unloading the module or disconnecting the USB device
> +	 */

The reason you run into this is likely because of the action added to
devm conflicting with hid_device_remove....

I recommend not depending on devm for teardown rather than making a stub
remove function to work around the issue.

  static void hid_device_remove(struct device *dev)
  {
    struct hid_device *hdev = to_hid_device(dev);
    struct hid_driver *hdrv;

    down(&hdev->driver_input_lock);
    hdev->io_started = false;

    hdrv = hdev->driver;
    if (hdrv) {
      if (hdrv->remove)
        hdrv->remove(hdev);
      else /* default remove */
        hid_hw_stop(hdev);

hid_device_remove will call hid_hw_stop and so will
mcp2200_hid_unregister because of the devm action you added.

> +}
> +
> +static const struct hid_device_id mcp2200_devices[] = {
> +	{ HID_USB_DEVICE(USB_VENDOR_ID_MICROCHIP, USB_DEVICE_ID_MCP2200) },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(hid, mcp2200_devices);
> +
> +static struct hid_driver mcp2200_driver = {
> +	.name		= "mcp2200",
> +	.id_table	= mcp2200_devices,
> +	.probe		= mcp2200_probe,
> +	.remove		= mcp2200_remove,
> +	.raw_event	= mcp2200_raw_event,
> +};
> +
> +/* Register with HID core */
> +module_hid_driver(mcp2200_driver);
> +
> +MODULE_AUTHOR("Johannes Roith <johannes@gnu-linux.rocks>");
> +MODULE_DESCRIPTION("MCP2200 Microchip HID USB to GPIO bridge");
> +MODULE_LICENSE("GPL");

--
Thanks,

Rahul Rameshbabu

Hi Rahul,

thanks for the feedback, I will add it to the driver.

> My personal recommendation is to just have a single DMA buffer allocated
> for the mcp2200 instance rather than having to call the allocator and
> release the memory per command.

I added an 16-byte Array hid_report to the mcp2000 struct. When I need the
report, I do the following:

struct mcp_set_clear_outputs *cmd;

mutex_lock(&mcp->lock);
cmd = (struct mcp_set_clear_outputs *) mcp->hid_report

Do you think this is a valid implementation or do I really have to add a
pointer to the mcp2200 struct instead of the 16 byte array and allocate 
another 16 byte for it in the probe function?

> The reason you run into this is likely because of the action added to
> devm conflicting with hid_device_remove....
> 
> I recommend not depending on devm for teardown rather than making a stub
> remove function to work around the issue.

I am not sure, if I have understand this correctly, but basically I already
have a stub remove function (which is empty). First the remove function gets
called, then the unregister function and everything is cleaned up correctly.
Did I get this right or do you have any other recommendation for me?

So, do I need any adaptions, or can we go with the empty remove function?

Best regards,
Johannes