All I've ever heard about Raspberry Pi is that its an "open source" SoC. But I see that the CPU inside the BroadCom SoC is an ARM chip.
My understanding of open source hardware is that every single hardware component on it has to be open source in order for the unit as a whole to be OSH. But if ARM is proprietary, then how can RPi be OSH?!?
Raspberry Pi has never maintained that the Pi is open source. There are many parts of it, especially the software, which are open source, but not everything is. There has been criticism of the Pi for having parts which are closed source, however given that the aim of the Pi is education of children, open sourcing everything is not seen as a priority.
Not sure where you got the impression that the Pi (or anything else for that matter) is 'open source HARDWARE' ..
For sure it's not .. it does however run Open Source Software on a SOC that includes a GPU with micro-code which is a closed source 'blob' (it has to be for two very good reasons - (1) you can perform H264, MPEG and VC1 video decode on the GPU (and that means a Licence Fee is REQUIRED to stay legal) and (2) the GPU silicon is an ancient design with a number of 'undocumented features' (so anyone changing the micro-code for one function risks 'breaking' it's operation in other, apparently unrelated, functions)
Whilst I would agree that not having access to the GPU microcode is a bit of a drawback, especially for anyone wanting to achieve any sort of real performance out of the Pi, it was never really aimed at anything other than School kids (apparently the 'hobbiest' came as a bit of an afterthought ..)
On the other hand, where else can you get so much 'free' software (and so much 'free' support) on a system for less than $30 ?
Here is an essential update now, as of January 2021. Raspberry Pi Foundation came up with "Raspberry Pi Pico" which is most open source:
Unlike the mostly open source, Broadcom based Raspberry Pi boards, the Raspberry Pi Pico is fully open source, with schematics and design files already posted. The exhaustively documented RP2040 chip is also far more open than any Broadcom processor. linuxgizmos.com
By the way, used in the board chip RP2040 custom designed by Raspberry Pi.
There are many different open source licenses out there. With each license, the definition of open source can be quite different with regard what needs to be shared and what needs to be allowed or denied from a reuse and redistribution standpoint.
Most of the hardware value provided by the Raspberry Pi is contained inside the Broadcom BCM2837 SoC (Raspberry Pi 3 and later, also used in some Raspberry Pi 2 revisions). This IC is not open sourced and for reasons that I am unfamiliar does not appear to have general market availability or documentation publicly available for it.
No major distributor lists this IC for sale, nor does Broadcom make the datasheet available for download on their website.
