DOCSIS. Absolutely nobody?

Hi all

It seems kind of strange to me that nobody has tried or is even attempting to get OpenWrt working for one of these DOCSIS modems.

Take for example this modem. It is selling for a dollar or two on ebay, literally.
SBG8300 SURFboard® DOCSIS® 3.1 Gigabit Modem & Wi-Fi® 6 Router

I know getting the actual DOCSIS module working is out of the question, but this modem has a regular
Broadcom BCM49xx soc and people are practically giving away their modems due to them being network locked.

I just opened mine and I see what looks to be like uart pins on the mainboard- is there some specific reason why nobody is pursuing this before I spend more time on it?

If the firmware DLds from the ISP, it's still not going to work, but you can always hope the bootloader's not locked.

If the bootloader is locked, one could try SPI flash, no?

Sure, assuming you've got something to flash it with.

The device you linked to has no ethernet WAN option, only 4 ethernet ports on a lan switch - if you can build an image maybe one of the ports can be made a WAN port, or maybe not.
If your plan is to use it as an access point then the factory firmware will do a better job than openwrt can as the wifi6 hardware is unlikely to have any opensource support, if the device is all broadcom.

There are other threads about attempts to create images for cable modem all in ones (search for 'cable modem'), they don't go anywhere as 1) the docsis hardware will never be supported and that's the most interesting part of the device and 2) these tend to be all broadcom devices with limited to zero mainline support.

It's your device so have at it - if you can get a working dts then openwrt should boot, how much functionality you have will depend on the amount of time and effort you want to spend.

Edit: there are two BCM49xxx devices in the TOH, they may help you get started. Neither has Wifi6.

There are two main issues with docsis and these devices:

  • it's pretty much always Broadcom, which means
    • no drivers for the cable/ docsis modem
    • no WLAN drivers
    • no FXS (analogue phone) drivers
    • no DECT drivers
    • for some of these SOCs a weird two-stage bootloader setup, which would require a non-redistributable second stage bootloader in the OpenWrt image
    • barely anyone who wants to put up with that hardware, investing quite a bit of quality time for the development, given that the best you could achieve, would be a wired-only router, which is rather on the slow side without Broadcom's proprietary acceleration (ctf.ko, no drivers for that either)
  • docsis modem drivers do need to authenticate themselves to the ISP via certificates, so even if the drivers were available (which they are not), you couldn't use them anyways, as you couldn't get them signed- and accepted by the ISP

There's no point looking into these.