How eDP Panel Self Refresh Conserves GPU Power

Panel Self Refresh (PSR) is an embedded DisplayPort (eDP) standard feature that reduces system energy consumption by offloading display refreshing from the graphics processor to the display panel itself during static screen conditions. In typical computing tasks such as reading documents or viewing static web pages, the screen image remains unchanged for extended periods. PSR allows the GPU, display engine, and main display transmission link to enter deep sleep states instead of continuously redrawing identical frames, resulting in significant battery savings in portable devices.

The Conventional Display Bottleneck

In a traditional display pipeline without PSR, the GPU must continuously generate and transmit video frames to the panel at the monitor's native refresh rate (e.g., 60Hz or 120Hz). This means the GPU renders and pushes the exact same image 60 to 120 times every second, even when the user is not interacting with the device. Maintaining this continuous data pipeline forces several power-hungry components to remain fully active:

  • The GPU's display rendering engines and pixel pipelines.
  • The GPU memory controller and system RAM to read the frame buffer.
  • The high-speed eDP Main Link lanes connecting the GPU to the display.

The Panel Self Refresh Mechanism

PSR breaks this cycle through hardware-level collaboration between the GPU and the display's Timing Controller (TCON). The process works through several distinct stages:

  1. Static Frame Detection: The graphics driver monitors the frame buffer. When it detects that no screen content has changed over a set number of frames, it initiates the transition to PSR mode.
  2. Capture to Remote Frame Buffer (RFB): The display panel's TCON contains an integrated memory module known as the Remote Frame Buffer (RFB), capable of holding at least one full frame of uncompressed pixel data. The GPU transmits the final static frame to the RFB.
  3. Display Handoff: Once the frame is completely stored in the RFB, the GPU instructs the TCON to take over local panel refreshing. The TCON autonomously reads the image from the RFB and drives the physical display panel.
  4. GPU Power Down: Because the TCON handles the refresh cycles independently, the GPU shuts down the high-speed eDP Main Link, dropping it into an ultralow-power standby state via Advanced Link Power Management (ALPM). Concurrently, the GPU clocks down its memory, display pipelines, and core logic, entering a low-power C-state or D-state.

Instant Wake and Partial Updates (PSR2)

When an update occurs—such as a keypress, mouse movement, or background notification—the GPU immediately wakes the eDP Main Link, transmits the updated frame data, and resumes standard driving operations.

Advanced iterations, such as PSR2, introduce Selective Update functionality. Instead of transferring a full frame when a minor change occurs (such as a blinking text cursor), the GPU only transmits the specific coordinates and pixel data of the modified region. The TCON updates only that portion of the RFB while maintaining the rest of the image. This minimizes the duration the eDP link and GPU need to be active, extending low-power residency even during lightweight interactive tasks.