AMD Prepares Linux Driver For New Feature: FreeSync Panel Replay

[phoronix]

Phoronix: AMD Prepares Linux Driver For New Feature: FreeSync Panel Replay

FreeSync Panel Replay is a new feature for AMD Ryzen laptops with the DCN v3.1.4 display block or newer for helping to reduce power usage when the screen contents are unchanged...

https://www.phoronix.com/news/AMD-Linux-FreeSync-Panel-Replay

[grigi]

On my external 4k display that supports 25-60Hz, when you turn on the display's fps counter it will drop down to 25fps when doing nothing, and using the display it will easily jump to 60fps or sync up with a 50hz video.

So this is just that, but at much lower frequencies? Does that mean that the minimum limit on adaptive-sync displays is basically disappearing?

[Anux]

On my external 4k display that supports 25-60Hz, when you turn on the display's fps counter it will drop down to 25fps when doing nothing, and using the display it will easily jump to 60fps or sync up with a 50hz video.

So this is just that, but at much lower frequencies? Does that mean that the minimum limit on adaptive-sync displays is basically disappearing?

No, this means as long as you do nothing (your desktop doesn't change) your GPU can go to sleep. While your monitor will still display 25 FPS (because it technically can't go lower), it doesn't need the GPU to deliver 25 times the same image. The monitor must have some kind of buffering to do so and understand the Panel Replay command.

[cl333r]

No, this means as long as you do nothing (your desktop doesn't change) your GPU can go to sleep. While your monitor will still display 25 FPS (because it technically can't go lower), it doesn't need the GPU to deliver 25 times the same image. The monitor must have some kind of buffering to do so and understand the Panel Replay command.

Is it only about OpenGL/Vulkan or does it also apply to regular GUI apps, if so does it mean that currently if you type nothing in (say) Kate it still sends at least 25 images per second to the GPU?

[grigi]

Ah, Thanks for the clarification.

[agd5f]

Is it only about OpenGL/Vulkan or does it also apply to regular GUI apps, if so does it mean that currently if you type nothing in (say) Kate it still sends at least 25 images per second to the GPU?

it's the display stream, so anything on the screen. If the screen is not changing, the monitor can just replay the same image over and and over until new content is sent from the GPU.

[Anux]

I don't know about inner workings/implementation details, that's just what I could get from news and google. But I think it has nothing to do with graphics API and comes in much later (display connection and frame buffer). Still there would need to be a method to recognise a change/static image, maybe just that the frame buffer doesn't get a new image but then sending the same image repeatedly to the frame buffer would fool this system.

[user556]

The driver software in the computer will command the display to preserve sections of the display's copy of the frame buffer. Yes, the monitor/TV has its own copy of the frame buffer, and always have had, from which it can do the scan conversion to suit the LCD panel inside.

None of this will apply to laptops since there the LCD panel is a direct connection, with the GPU maintaining the minimum refresh rate to keep the pixel drivers in balance.

[Venemo]

Is there any existing HW that supports this feature? If yes, what?

[loganj]

is there any use of lower fps when nothing happens? does it save power? or what?