This problem happens on a laptop with AMD e-350 APU and built-in radeon HD 6310 graphics. It runs Slackware64 version 14.0. On the console (VTs), KMS is used with the radeon driver.
The problem occurs when using a 3.10.* series kernel. If console screen blanking is enabled (e.g.,
setterm -blank or kernel parameter
consoleblank=) then when the screen blanks, it momentarily becomes black as it should, but after a second or less turns entirely white and remains that way until it unblanks. I've experimented and searched the web without any success at solving this.
I will add that the screen blanks properly if either (a) KMS is disabled and the console video is configured with
vga=, or (b) a 3.2.* series kernel is used with KMS. These possibilities are less desirable for my use, for various reasons. I'd like to get it working right with 3.10.* kernels.
I'd welcome any suggestions. I can also give more info if needed.