Qualcomm was very supportive of us and provided documentation, technical support, etc, while we did the coreLinux port for MSM7X0X and MSM8X50. Since then they've become much more involved and are not working directly with the community, submitting patches on lkml, etc. Which is great!
Obviously some vendors already had code in mainline or patchsets available and others were not as far along, but overall Linux had a lot of momentum and there was plenty of interest in enabling it, even back in 2005. Since then it's only picked up even more steam, between Android, WebOS, MeeGo, etc.