Communication with CDC ACM device on Linux via USB - c

Question

I've got some serial device connected via CDC-ACM USB device so it is possible to communicate with it via /dev/ttyACM1 from Linux perspective.
The end device is the device which contains RTC which allows me to get the current date and time from it via CDC-ACM. It is working fine form user space.
Below is the device descriptor of my CDC-ACM USB device:
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 2
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0xyyyy
idProduct 0xzzzz
bcdDevice 2.00
iManufacturer 1 xxxxxxxxxxxxxx
iProduct 2 yyyyyyyyyyyyyy
iSerial 3 zzzzzzzzzzzzzz
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 67
bNumInterfaces 2
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 2
bInterfaceSubClass 2
bInterfaceProtocol 1
iInterface 0
CDC Header:
bcdCDC 1.10
CDC Call Management:
bmCapabilities 0x00
bDataInterface 1
CDC ACM:
bmCapabilities 0x02
line coding and serial state
CDC Union:
bMasterInterface 0
bSlaveInterface 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0008 1x 8 bytes
bInterval 255
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 10
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Device Status: 0x0001
Self Powered
Now - I'd like to set date and time via this CDC-ACM connection using kernel API via USB. I thought that it is enough to send the same request string for date and time via bulk-out ep1 and receive the response via bulk-in ep81. I tried to do it with usb_bulk_msg() and when I'm sending request string with this proc - it returns 0. Next, when I'm sending request for reading response from this device I get -110 (-ETIMEDOUT).
Seems like the linux kernel is sending my first request properly because it returns 0, but for some reasons this request is not received by the end device because it doesn't responded with anything because timeout (-110) occured.
I'm wondering if I didn't miss something with my code and that is why it is not working. Any ideas what can be wrong?
Is it enough to use just only bulk-in and bulk-out endpoints to communicate with end device or anything else should be done before the right transmission?