Most Radeon Evergreen and Northern Island cards support power-saving modes with Linux and XOrg well, and have done for years. But if a dual link DVI monitor is in use (e.g. a 2560x1440 or 2560x1600 screen), the card will refuse to transition out of its high power mode while the display is active. I believe that this is because transitions are not supported when multiple displays are active, and dual link DVI is counted as being two displays. If so, this seems wrong as the main issue with multiple displays is the difficulty of arranging to change the mclk when neither is mid-way through a scan line. With DL-DVI the two links are perfectly synchronised, and so this issue does not arise. Unsurprisingly the cards do enter their low-power state when their output is off (e.g. "xset dpms force off"), but more surprisingly on awakening they remain in their low power state. The slightest provocation then causes a permanent transition to the high power state, showing that transitions with the display active work, and are invisible. One can force them to run in their low power state by echo low > /sys/class/drm/card0/device/power_dpm_force_performance_level when they are already in the low power state. On many cards this provides adequate performance for most office-type applications, but it is hopeless at supporting any form of video. So would it be possible to permit the high power to low power transition even when a DL-DVI display is active? (I believe that the AMDGPU driver gained the ability to do power level transitions with multiple synchonrised displays back in 2019 with amdgpu.dcfeaturemask=2 but I am unaware that the change was made to the older radeon driver, and DL-DVI is hardly two displays anyway.) (Why do I care? I am responsible for several dozen machines with these cards, as, if one wants a cheap, passively-cooled card with good support from the free XOrg drivers, they are still quite good. I believe that the R5 230 is still in production too. The sort of office applications these machines display would allow the cards to stay in their low-power state most of the time, but not quite all of it. In the past most of our machines tended to have a single 1920x1080 monitor, so this did not matter, but now 2.5k monitors are becoming more common. AMD's habit of launching new CPUs some months before the corresponding APUs means that our need of simple passively-cooled cards is still quite current, as our programs do like the latest CPUs.) Issue present on X.Org 1.21.1.3 radeon module 19.1.0 on Ubuntu 22.04 x86_64. Regards, Michael -- Dr MJ Rutter, TCM, Cavendish Lab, JJ Thomson Av, Cambridge. CB3 0HE Email: mjr19@xxxxxxxxx Ph: 01223 337386 https://www.mjr19.org.uk/
