Hi Peter,
i didn't subscribe to dri-devel, but i noticed your bug report.
Could you please provide more information:
Which kernel config do you use (is it a defconfig)? Do you use the mainline device tree blob or the Raspberry Pi DTB? Please provide the version/date of the GPU firmware? Do you have any KMS related setting in the config.txt? Can you provide a full dmesg for the bad case?
Best regards