I am using raspberry pi 4b after successfully installation of raspbian os i connected the pi with raspberry display (official raspberry pi 7 inch display) then error msg appears as kernel panic cant allocate swiotlb buffer before and cant allocate dmabouncer buffer now Please help
I ran into this same issue with a new install of Pi OS after setting the GPU memory to 896 MB in raspi-config.
To fix it without reinstalling:
Put the SD card in another computer that can read the "boot" filesystem. I believe it is a FAT32 filesystem.
Open "config.txt" and alter the "gpu_mem" setting. Set it to something like 512 or lower.
I don't know what the upper limit is, but 512 worked for me and is recommended as the maximum value for a Pi with 1GB memory or greater.