AMD Updates FreeSync Panel Replay Support For Linux

Last month AMD Linux kernel driver patches revealed a new feature called FreeSync Panel Replay that is basically an improvement over Panel Self Refresh (PSR) for laptop displays. That code didn't make it for the recently-closed v6.5 merge window but this week AMD engineers did post a second iteration of the patches.

Published on Monday were FreeSync Panel Replay v2 patches for the AMDGPU Linux kernel driver's display code. The updated code for enabling FreeSync Panel Replay fixes issues around an invisible cursor, laggy systems, and random hangs. It's looking like this second attempt at the FreeSync Panel Replay for Linux is in much better -- and useful -- shape for this feature being found with the DCN 3.1.4 display block and newer.

Per the patch series, FreeSync Panel Replay is summed up as:

The importance of Replay
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In some instances, the GPU is transmitting repeated frames to the sink without any updates or changes in the content. These repeat transmission are wasteful, resulting in power draw in different aspects of the system

1. DCN is fetching the frame of data from DF/UMC/DRAM. This memory traffic prevents power down of parts of this HW path.

2. GPU is transmitting pixel data to the display through the main link of the DisplayPort interface. This prevents power down of both the Source transmitter (TX) and the Sink receiver (RX)

How it improves on PSR
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The concepts of utilizing replay is similar to PSR, but there is a benefit of:
Source and Sink remaining synchronized which allows for
- lower latency when switching from replay to live frames
- enable the possibility of more use cases
- easy control of the sink's refresh rate during replay

Overall this should be a nice win for new AMD Ryzen laptops when the systems begin appearing with this FreeSync Panel Replay support. The updated patches can be found on the amd-gfx mailing list while hopefully will be ready for merging with the Linux 6.6 cycle.