I found out about this while browsing the modding thread for this laptop on the TechInferno forums. Apparently, a user was in contact with engineers at HP, who claimed the WWAN card slot was at one point wired for mSATA, but the traces were cut and the BIOS whitelist doesn't allow you to use one.
The motherboard traces remain, but with solder joints where 0-ohm resistors would go if they decided to re-enable this feature at any point during manufacturing. If reconnected, all neccesary pins on the WWAN card slot would be electrically connected to the SATA controller. However, the BIOS will still block this, and since it is RSA signed noone on TechInferno seems to successfully modified the whitelist to get this working.
Well, who needs to modify a BIOS whitelist when you can replace the BIOS entirely?
By default coreboot has been hard-coded to disable unused SATA ports. You will have to modify a file called overridetree.cb to tell the SATA controller to enable it. I use libreboot, unsure if that matters to you, but for me the file was located in coreboot/src/mainboard/hp/snb_ivb_laptops/variants/2570p
In overridetree.cb, find a variable register "sata_port_map", replace the value with 0x3f.
Again, that should be: register "sata_port_map" = "0x3f"
Why 0x3f? Well, I don't really know, but some random reddit post I read said that the SATA port map is a 6 bit binary interger, represented here in hex. Each bit represents a SATA port to be enabled or disabled. Keeping the value at 111111 will just turn on all SATA ports. This is of course the lazy way, but I don't know which bits correspond to what SATA ports. Contact me if you know which bits correspond to what SATA ports or have a better idea here in general.
For this part of the guide, I'll leave you with the following image, from pandaleo on TechInferno. This is what I followed, although I just solder-blobbed it instead of adding the resistors (why bother?) I am not educated enough to give you proper soldering advice, and you can find a better disassembly guide somewhere else. I strongly reccomend dissasembling enough to expose the motherboard more, but if you can do it through the window under the modem (with seemingly a crosshair pointing right at them,) contact me! I'll have no prize for you, but I'd sure like to see you try!
