AMD Prepares Linux Driver For New Feature: FreeSync Panel Replay
While there is already power-savings tech like Panel Self Refresh (PSR) with modern laptops to help reduce power usage when the screen contents are static, FreeSync Panel Replay is a new offering with Display Core Next 3.1.4+ hardware to help in similar scenarios. The open-source driver patches though do note that FreeSync Panel Replay cannot be used when PSR is active. AMD views this new FreeSync Panel Replay feature as superior to PSR because the source and sink remain synchronized to allow for lower latency when switching out of the mode, can handle more use-cases, and easier control of the sink's refresh rate.
The AMD patch cover letter describes FreeSync Panel Replay as:
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)
It will be interesting to see how much of a power advantage FreeSync Panel Replay has in comparison to Panel Self Refresh. Prior to seeing these FreeSync Panel Replay patches yesterday, I haven't heard AMD talk up this feature nor has there been any results within the search engines.
The patch series is around one thousand lines of new code. Though due to the timing of these AMDGPU kernel driver patches, they aren't expected to be mainlined now until at least the v6.6 kernel cycle later in the year.
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