What do you mean by same results? (Note, Im not sure I was 100% clear; these arent my print messages; they are the print messages resulting from turning CONFIG_MMC_DEBUG=y in the kernel config)
Also, I dont have a /etc/kmsg file in my build for some reason, is there something I have to do to get that file (aside from messing with a few kernel configs like those mentioned above, this is a pretty vanilla yocto build out of bitbake)?
So, I "fixed" this issue by replacing all the pr_debug messages with pr_info instead, after setting the kernel command line to have loglevel 7 instead of loglevel 4. Once I remade the image with my modifications (just a find and replace across all the files in the mmc driver), I was able to have all the debug messages print to Putty whose buffer I made REALLY big