Re: [PATCH v3 1/7] mfd: Add core driver for Nuvoton NCT6694

Mateusz Polchlopek
2024-12-10T10:57:57Z

On 12/10/2024 11:45 AM, Ming Yu wrote:
> The Nuvoton NCT6694 is a peripheral expander with 16 GPIO chips,
> 6 I2C controllers, 2 CANfd controllers, 2 Watchdog timers, ADC,
> PWM, and RTC.
>
> This driver implements USB device functionality and shares the
> chip's peripherals as a child device.
>
> Each child device can use the USB functions nct6694_read_msg()
> and nct6694_write_msg() to issue a command. They can also request
> interrupt that will be called when the USB device receives its
> interrupt pipe.
>
> Signed-off-by: Ming Yu <tmyu0@nuvoton.com>
> ---
> MAINTAINERS | 7 +
> drivers/mfd/Kconfig | 10 +
> drivers/mfd/Makefile | 2 +
> drivers/mfd/nct6694.c | 382 ++++++++++++++++++++++++++++++++++++
> include/linux/mfd/nct6694.h | 139 +++++++++++++
> 5 files changed, 540 insertions(+)
> create mode 100644 drivers/mfd/nct6694.c
> create mode 100644 include/linux/mfd/nct6694.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 67d2159406c2..9c9a94ff8f98 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -16541,6 +16541,13 @@ F: drivers/nubus/
> F: include/linux/nubus.h
> F: include/uapi/linux/nubus.h
>
> +NUVOTON NCT6694 MFD DRIVER
> +M: Ming Yu <tmyu0@nuvoton.com>
> +L: linux-kernel@vger.kernel.org
> +S: Supported
> +F: drivers/mfd/nct6694.c
> +F: include/linux/mfd/nct6694.h
> +
> NVIDIA (rivafb and nvidiafb) FRAMEBUFFER DRIVER
> M: Antonino Daplas <adaplas@gmail.com>
> L: linux-fbdev@vger.kernel.org
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index 03c1e4e3eea4..07ccc32f9985 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -558,6 +558,16 @@ config MFD_MX25_TSADC
> i.MX25 processors. They consist of a conversion queue for general
> purpose ADC and a queue for Touchscreens.
>
> +config MFD_NCT6694
> + tristate "Nuvoton NCT6694 support"
> + select MFD_CORE
> + depends on USB
> + help
> + This adds support for Nuvoton USB device NCT6694 sharing peripherals
> + This includes the USB devcie driver and core APIs.
> + Additional drivers must be enabled in order to use the functionality
> + of the device.
> +
> config MFD_HI6421_PMIC
> tristate "HiSilicon Hi6421 PMU/Codec IC"
> depends on OF
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index e057d6d6faef..9d0365ba6a26 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -117,6 +117,8 @@ obj-$(CONFIG_TWL6040_CORE) += twl6040.o
>
> obj-$(CONFIG_MFD_MX25_TSADC) += fsl-imx25-tsadc.o
>
> +obj-$(CONFIG_MFD_NCT6694) += nct6694.o
> +
> obj-$(CONFIG_MFD_MC13XXX) += mc13xxx-core.o
> obj-$(CONFIG_MFD_MC13XXX_SPI) += mc13xxx-spi.o
> obj-$(CONFIG_MFD_MC13XXX_I2C) += mc13xxx-i2c.o
> diff --git a/drivers/mfd/nct6694.c b/drivers/mfd/nct6694.c
> new file mode 100644
> index 000000000000..071333d13eae
> --- /dev/null
> +++ b/drivers/mfd/nct6694.c
> @@ -0,0 +1,382 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Nuvoton NCT6694 MFD driver based on USB interface.
> + *
> + * Copyright (C) 2024 Nuvoton Technology Corp.
> + */
> +
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/irqdomain.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/core.h>
> +#include <linux/mfd/nct6694.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/usb.h>
> +
> +#define MFD_DEV_SIMPLE(_name) \
> +{ \
> + .name = NCT6694_DEV_##_name, \
> +} \
> +
> +#define MFD_DEV_WITH_ID(_name, _id) \
> +{ \
> + .name = NCT6694_DEV_##_name, \
> + .id = _id, \
> +}
> +
> +/* MFD device resources */
> +static const struct mfd_cell nct6694_dev[] = {
> + MFD_DEV_WITH_ID(GPIO, 0x0),
> + MFD_DEV_WITH_ID(GPIO, 0x1),
> + MFD_DEV_WITH_ID(GPIO, 0x2),
> + MFD_DEV_WITH_ID(GPIO, 0x3),
> + MFD_DEV_WITH_ID(GPIO, 0x4),
> + MFD_DEV_WITH_ID(GPIO, 0x5),
> + MFD_DEV_WITH_ID(GPIO, 0x6),
> + MFD_DEV_WITH_ID(GPIO, 0x7),
> + MFD_DEV_WITH_ID(GPIO, 0x8),
> + MFD_DEV_WITH_ID(GPIO, 0x9),
> + MFD_DEV_WITH_ID(GPIO, 0xA),
> + MFD_DEV_WITH_ID(GPIO, 0xB),
> + MFD_DEV_WITH_ID(GPIO, 0xC),
> + MFD_DEV_WITH_ID(GPIO, 0xD),
> + MFD_DEV_WITH_ID(GPIO, 0xE),
> + MFD_DEV_WITH_ID(GPIO, 0xF),
> +
> + MFD_DEV_WITH_ID(I2C, 0x0),
> + MFD_DEV_WITH_ID(I2C, 0x1),
> + MFD_DEV_WITH_ID(I2C, 0x2),
> + MFD_DEV_WITH_ID(I2C, 0x3),
> + MFD_DEV_WITH_ID(I2C, 0x4),
> + MFD_DEV_WITH_ID(I2C, 0x5),
> +
> + MFD_DEV_WITH_ID(CAN, 0x0),
> + MFD_DEV_WITH_ID(CAN, 0x1),
> +
> + MFD_DEV_WITH_ID(WDT, 0x0),
> + MFD_DEV_WITH_ID(WDT, 0x1),
> +
> + MFD_DEV_SIMPLE(HWMON),
> + MFD_DEV_SIMPLE(RTC),
> +};
> +
> +static int nct6694_response_err_handling(struct nct6694 *nct6694,
> + unsigned char err_status)
> +{
> + struct device *dev = &nct6694->udev->dev;
> +
> + switch (err_status) {
> + case NCT6694_NO_ERROR:
> + return err_status;
> + case NCT6694_NOT_SUPPORT_ERROR:
> + dev_dbg(dev, "%s: Command is not support!\n", __func__);
> + break;
> + case NCT6694_NO_RESPONSE_ERROR:
> + dev_dbg(dev, "%s: Command is no response!\n", __func__);
> + break;
> + case NCT6694_TIMEOUT_ERROR:
> + dev_dbg(dev, "%s: Command is timeout!\n", __func__);
> + break;
> + case NCT6694_PENDING:
> + dev_dbg(dev, "%s: Command is pending!\n", __func__);
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + return -EIO;
> +}
> +
> +int nct6694_read_msg(struct nct6694 *nct6694, u8 mod, u16 offset,
> + u16 length, void *buf)
> +{
> + struct nct6694_cmd_header *cmd_header = nct6694->cmd_header;
> + struct nct6694_response_header *response_header = nct6694->response_header;

RCT violation

> + struct usb_device *udev = nct6694->udev;
> + int tx_len, rx_len, ret;
> +
> + guard(mutex)(&nct6694->access_lock);
> +
> + /* Send command packet to USB device */
> + cmd_header->mod = mod;
> + cmd_header->cmd = offset & 0xFF;
> + cmd_header->sel = (offset >> 8) & 0xFF;
> + cmd_header->hctrl = NCT6694_HCTRL_GET;
> + cmd_header->len = length;
> +
> + ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, NCT6694_BULK_OUT_EP),
> + cmd_header, NCT6694_CMD_PACKET_SZ, &tx_len,
> + nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + /* Receive response packet from USB device */
> + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, NCT6694_BULK_IN_EP),
> + response_header, NCT6694_CMD_PACKET_SZ, &rx_len,
> + nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, NCT6694_BULK_IN_EP),
> + buf, NCT6694_MAX_PACKET_SZ, &rx_len, nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + return nct6694_response_err_handling(nct6694, response_header->sts);
> +}
> +EXPORT_SYMBOL(nct6694_read_msg);
> +
> +int nct6694_write_msg(struct nct6694 *nct6694, u8 mod, u16 offset,
> + u16 length, void *buf)
> +{
> + struct nct6694_cmd_header *cmd_header = nct6694->cmd_header;
> + struct nct6694_response_header *response_header = nct6694->response_header;

Same as above

> + struct usb_device *udev = nct6694->udev;
> + int tx_len, rx_len, ret;
> +
> + guard(mutex)(&nct6694->access_lock);
> +
> + /* Send command packet to USB device */
> + cmd_header->mod = mod;
> + cmd_header->cmd = offset & 0xFF;
> + cmd_header->sel = (offset >> 8) & 0xFF;
> + cmd_header->hctrl = NCT6694_HCTRL_SET;
> + cmd_header->len = length;
> +
> + ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, NCT6694_BULK_OUT_EP),
> + cmd_header, NCT6694_CMD_PACKET_SZ, &tx_len,
> + nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, NCT6694_BULK_OUT_EP),
> + buf, length, &tx_len, nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + /* Receive response packet from USB device */
> + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, NCT6694_BULK_IN_EP),
> + response_header, NCT6694_CMD_PACKET_SZ, &rx_len,
> + nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, NCT6694_BULK_IN_EP),
> + buf, NCT6694_MAX_PACKET_SZ, &rx_len, nct6694->timeout);
> + if (ret)
> + return ret;
> +
> + return nct6694_response_err_handling(nct6694, response_header->sts);
> +}
> +EXPORT_SYMBOL(nct6694_write_msg);
> +
> +static void usb_int_callback(struct urb *urb)
> +{
> + struct nct6694 *nct6694 = urb->context;
> + struct device *dev = &nct6694->udev->dev;
> + unsigned int *int_status = urb->transfer_buffer;

Again RCT violation

> + int ret;
> +
> + switch (urb->status) {
> + case 0:
> + break;
> + case -ECONNRESET:
> + case -ENOENT:
> + case -ESHUTDOWN:
> + return;
> + default:
> + goto resubmit;
> + }
> +
> + while (*int_status) {
> + int irq = __ffs(*int_status);
> +
> + if (*int_status & (1 << irq))
> + generic_handle_irq_safe(irq_find_mapping(nct6694->domain, irq));
> +
> + *int_status &= ~(1 << irq);
> + }
> +
> +resubmit:
> + ret = usb_submit_urb(urb, GFP_ATOMIC);
> + if (ret)
> + dev_dbg(dev, "%s: Failed to resubmit urb, status %d",
> + __func__, ret);
> +}
> +
> +static void nct6694_irq_lock(struct irq_data *data)
> +{
> + struct nct6694 *nct6694 = irq_data_get_irq_chip_data(data);
> +
> + mutex_lock(&nct6694->irq_lock);
> +}
> +
> +static void nct6694_irq_sync_unlock(struct irq_data *data)
> +{
> + struct nct6694 *nct6694 = irq_data_get_irq_chip_data(data);
> +
> + mutex_unlock(&nct6694->irq_lock);
> +}
> +
> +static void nct6694_irq_enable(struct irq_data *data)
> +{
> + struct nct6694 *nct6694 = irq_data_get_irq_chip_data(data);
> + unsigned int irq = data->hwirq;
> +
> + nct6694->irq_enable |= (1 << irq);

I wonder if this is necessary to create local variable irq
if this is used only once. Maybe instead:

nct6694->irq_enable |= (1 << data->hwirq);

Not big thing though

> +}
> +
> +static void nct6694_irq_disable(struct irq_data *data)
> +{
> + struct nct6694 *nct6694 = irq_data_get_irq_chip_data(data);
> + unsigned int irq = data->hwirq;
> +
> + nct6694->irq_enable &= ~(1 << irq);
> +}
> +
> +static struct irq_chip nct6694_irq_chip = {
> + .name = "nct6694-irq",
> + .flags = IRQCHIP_SKIP_SET_WAKE,
> + .irq_bus_lock = nct6694_irq_lock,
> + .irq_bus_sync_unlock = nct6694_irq_sync_unlock,
> + .irq_enable = nct6694_irq_enable,
> + .irq_disable = nct6694_irq_disable,
> +};
> +
> +static int nct6694_irq_domain_map(struct irq_domain *d, unsigned int irq,
> + irq_hw_number_t hw)
> +{
> + struct nct6694 *nct6694 = d->host_data;
> +
> + irq_set_chip_data(irq, nct6694);
> + irq_set_chip_and_handler(irq, &nct6694_irq_chip, handle_simple_irq);
> +
> + return 0;
> +}
> +
> +static void nct6694_irq_domain_unmap(struct irq_domain *d, unsigned int irq)
> +{
> + irq_set_chip_and_handler(irq, NULL, NULL);
> + irq_set_chip_data(irq, NULL);
> +}
> +
> +static const struct irq_domain_ops nct6694_irq_domain_ops = {
> + .map = nct6694_irq_domain_map,
> + .unmap = nct6694_irq_domain_unmap,
> +};
> +
> +static int nct6694_usb_probe(struct usb_interface *iface,
> + const struct usb_device_id *id)
> +{
> + struct usb_device *udev = interface_to_usbdev(iface);
> + struct device *dev = &udev->dev;
> + struct usb_host_interface *interface;
> + struct usb_endpoint_descriptor *int_endpoint;
> + struct nct6694 *nct6694;
> + struct nct6694_cmd_header *cmd_header;
> + struct nct6694_response_header *response_header;
> + int pipe, maxp;
> + int ret;

Please follow RCT rule

> +
> + interface = iface->cur_altsetting;
> +
> + int_endpoint = &interface->endpoint[0].desc;
> + if (!usb_endpoint_is_int_in(int_endpoint))
> + return -ENODEV;
> +
> + nct6694 = devm_kzalloc(dev, sizeof(*nct6694), GFP_KERNEL);
> + if (!nct6694)
> + return -ENOMEM;
> +
> + pipe = usb_rcvintpipe(udev, NCT6694_INT_IN_EP);
> + maxp = usb_maxpacket(udev, pipe);
> +
> + cmd_header = devm_kzalloc(dev, sizeof(*cmd_header),
> + GFP_KERNEL);
> + if (!cmd_header)
> + return -ENOMEM;
> +
> + response_header = devm_kzalloc(dev, sizeof(*response_header),
> + GFP_KERNEL);
> + if (!response_header)
> + return -ENOMEM;
> +
> + nct6694->int_buffer = devm_kcalloc(dev, NCT6694_MAX_PACKET_SZ,
> + sizeof(unsigned char), GFP_KERNEL);
> + if (!nct6694->int_buffer)
> + return -ENOMEM;
> +
> + nct6694->int_in_urb = usb_alloc_urb(0, GFP_KERNEL);
> + if (!nct6694->int_in_urb)
> + return -ENOMEM;> +
> + nct6694->domain = irq_domain_add_simple(NULL, NCT6694_NR_IRQS, 0,
> + &nct6694_irq_domain_ops,
> + nct6694);
> + if (!nct6694->domain)
> + return -ENODEV;
> +
> + nct6694->udev = udev;
> + nct6694->timeout = NCT6694_URB_TIMEOUT; /* Wait until urb complete */
> + nct6694->cmd_header = cmd_header;
> + nct6694->response_header = response_header;
> +
> + mutex_init(&nct6694->access_lock);
> + mutex_init(&nct6694->irq_lock);
> +
> + usb_fill_int_urb(nct6694->int_in_urb, udev, pipe,
> + nct6694->int_buffer, maxp, usb_int_callback,
> + nct6694, int_endpoint->bInterval);
> + ret = usb_submit_urb(nct6694->int_in_urb, GFP_KERNEL);
> + if (ret)
> + goto err_urb;
> +
> + dev_set_drvdata(dev, nct6694);
> + usb_set_intfdata(iface, nct6694);
> +
> + ret = mfd_add_hotplug_devices(dev, nct6694_dev, ARRAY_SIZE(nct6694_dev));
> + if (ret)
> + goto err_mfd;
> +
> + dev_info(dev, "Probed device: (%04X:%04X)\n", id->idVendor, id->idProduct);
> + return 0;
> +
> +err_mfd:
> + usb_kill_urb(nct6694->int_in_urb);
> +err_urb:
> + usb_free_urb(nct6694->int_in_urb);
> + return dev_err_probe(dev, ret, "Probe failed\n");
> +}
> +
> +static void nct6694_usb_disconnect(struct usb_interface *iface)
> +{
> + struct usb_device *udev = interface_to_usbdev(iface);
> + struct nct6694 *nct6694 = usb_get_intfdata(iface);
> +
> + mfd_remove_devices(&udev->dev);
> + usb_kill_urb(nct6694->int_in_urb);
> + usb_free_urb(nct6694->int_in_urb);
> +}
> +
> +static const struct usb_device_id nct6694_ids[] = {
> + { USB_DEVICE_AND_INTERFACE_INFO(NCT6694_VENDOR_ID,
> + NCT6694_PRODUCT_ID,
> + 0xFF, 0x00, 0x00)},
> + {}
> +};
> +MODULE_DEVICE_TABLE(usb, nct6694_ids);
> +
> +static struct usb_driver nct6694_usb_driver = {
> + .name = "nct6694",
> + .id_table = nct6694_ids,
> + .probe = nct6694_usb_probe,
> + .disconnect = nct6694_usb_disconnect,
> +};
> +
> +module_usb_driver(nct6694_usb_driver);
> +
> +MODULE_DESCRIPTION("USB-MFD driver for NCT6694");
> +MODULE_AUTHOR("Ming Yu <tmyu0@nuvoton.com>");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/mfd/nct6694.h b/include/linux/mfd/nct6694.h
> new file mode 100644
> index 000000000000..9733d47f5a01
> --- /dev/null
> +++ b/include/linux/mfd/nct6694.h
> @@ -0,0 +1,139 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Nuvoton NCT6694 USB transaction and data structure.
> + *
> + * Copyright (C) 2024 Nuvoton Technology Corp.
> + */
> +
> +#ifndef __MFD_NCT6694_H
> +#define __MFD_NCT6694_H
> +
> +#define NCT6694_DEV_GPIO "nct6694-gpio"
> +#define NCT6694_DEV_I2C "nct6694-i2c"
> +#define NCT6694_DEV_CAN "nct6694-can"
> +#define NCT6694_DEV_WDT "nct6694-wdt"
> +#define NCT6694_DEV_HWMON "nct6694-hwmon"
> +#define NCT6694_DEV_RTC "nct6694-rtc"
> +
> +#define NCT6694_VENDOR_ID 0x0416
> +#define NCT6694_PRODUCT_ID 0x200B
> +#define NCT6694_INT_IN_EP 0x81
> +#define NCT6694_BULK_IN_EP 0x02
> +#define NCT6694_BULK_OUT_EP 0x03
> +#define NCT6694_MAX_PACKET_SZ 0x200
> +
> +#define NCT6694_CMD_PACKET_SZ 0x8
> +#define NCT6694_HCTRL_SET 0x40
> +#define NCT6694_HCTRL_GET 0x80
> +
> +#define NCT6694_URB_TIMEOUT 1000
> +
> +enum nct6694_irq_id {
> + NCT6694_IRQ_GPIO0 = 0,
> + NCT6694_IRQ_GPIO1,
> + NCT6694_IRQ_GPIO2,
> + NCT6694_IRQ_GPIO3,
> + NCT6694_IRQ_GPIO4,
> + NCT6694_IRQ_GPIO5,
> + NCT6694_IRQ_GPIO6,
> + NCT6694_IRQ_GPIO7,
> + NCT6694_IRQ_GPIO8,
> + NCT6694_IRQ_GPIO9,
> + NCT6694_IRQ_GPIOA,
> + NCT6694_IRQ_GPIOB,
> + NCT6694_IRQ_GPIOC,
> + NCT6694_IRQ_GPIOD,
> + NCT6694_IRQ_GPIOE,
> + NCT6694_IRQ_GPIOF,
> + NCT6694_IRQ_CAN1,
> + NCT6694_IRQ_CAN2,
> + NCT6694_IRQ_RTC,
> + NCT6694_NR_IRQS,
> +};
> +
> +enum nct6694_response_err_status {
> + NCT6694_NO_ERROR = 0,
> + NCT6694_FORMAT_ERROR,
> + NCT6694_RESERVED1,
> + NCT6694_RESERVED2,
> + NCT6694_NOT_SUPPORT_ERROR,
> + NCT6694_NO_RESPONSE_ERROR,
> + NCT6694_TIMEOUT_ERROR,
> + NCT6694_PENDING,
> +};
> +
> +struct nct6694 {
> + struct usb_device *udev;
> + struct urb *int_in_urb;
> + struct irq_domain *domain;
> + struct nct6694_cmd_header *cmd_header;
> + struct nct6694_response_header *response_header;
> + struct mutex access_lock;
> + struct mutex irq_lock;
> + unsigned char *int_buffer;
> + unsigned int irq_enable;
> + /* time in msec to wait for the urb to the complete */
> + long timeout;
> +};
> +
> +struct nct6694_cmd_header {
> + unsigned char rsv1;
> + unsigned char mod;
> + unsigned char cmd;
> + unsigned char sel;
> + unsigned char hctrl;
> + unsigned char rsv2;
> + unsigned short len;
> +} __packed;
> +
> +struct nct6694_response_header {
> + unsigned char sequence_id;
> + unsigned char sts;
> + unsigned int rsv;
> + unsigned short len;
> +} __packed;
> +
> +/*
> + * nct6694_read_msg - Receive data from NCT6694 USB device
> + *
> + * @nct6694 - Nuvoton NCT6694 structure
> + * @mod - Module byte
> + * @offset - Offset byte or (Select byte | Command byte)
> + * @length - Length byte
> + * @buf - Read data from rx buffer
> + *
> + * USB Transaction format:
> + *
> + * OUT |RSV|MOD|CMD|SEL|HCTL|RSV|LEN_L|LEN_H|
> + * OUT |SEQ|STS|RSV|RSV|RSV|RSV||LEN_L|LEN_H|
> + * IN |-------D------A------D------A-------|
> + * IN ......
> + * IN |-------D------A------D------A-------|
> + */
> +int nct6694_read_msg(struct nct6694 *nct6694, u8 mod, u16 offset,
> + u16 length, void *buf);
> +
> +/*
> + * nct6694_read_msg - Transmit data to NCT6694 USB device
> + *
> + * @nct6694 - Nuvoton NCT6694 structure
> + * @mod - Module byte
> + * @offset - Offset byte or (Select byte | Command byte)
> + * @length - Length byte
> + * @buf - Write data to tx buffer
> + *
> + * USB Transaction format:
> + *
> + * OUT |RSV|MOD|CMD|SEL|HCTL|RSV|LEN_L|LEN_H|
> + * OUT |-------D------A------D------A-------|
> + * OUT ......
> + * OUT |-------D------A------D------A-------|
> + * IN |SEQ|STS|RSV|RSV|RSV|RSV||LEN_L|LEN_H|
> + * IN |-------D------A------D------A-------|
> + * IN ......
> + * IN |-------D------A------D------A-------|
> + */
> +int nct6694_write_msg(struct nct6694 *nct6694, u8 mod, u16 offset,
> + u16 length, void *buf);
> +
> +#endif