The relationship is very clear: Upton was a Broadcom FAE that started the RPi Foundation. The secondary story was that he found a use for an orphaned SoC and embarked on an 'educational' quest to make small computers for classrooms.

The real question is if Broadcom is devoting internal software resources to improving the ecosystem, or if it's coming from the devoted users. I don't track commits on kernel.org enough to know what's what.