Intel® graphics drivers and software, compatibility, troubleshooting, performance, and optimization
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Unable to enable hardware overlay




I'd like to write an OS driver to enable the hardware overlay to show my own images on top of OS and all other applications. So I programmed the plane 2's registers of PLANE_* as described in the programming manual intel-gfx-prm-osrc-kbl-vol02c-commandreference-registers-part2_0.pdf. However, the GPU immediately outputs nothing or glitch images, and Linux kernel also reports "[ 1099.357307] i915 0000:00:02.0: [drm] *ERROR* CPU pipe A FIFO underrun".


My CPU is i5-7600.

My GPU is "VGA compatible controller: Intel Corporation HD Graphics 630 (rev 04) (prog-if 00 [VGA controller]) Subsystem: Dell HD Graphics 630". The BAR0 is "Region 0: Memory at ee000000 (64-bit, non-prefetchable) [size=16M]".

The GPU connects to only one monitor thru HDMI.


I tried the following MMIO writes in both Ubuntu 22.04 x64 (thru intel-gpu-tools) and Win10 x64 (thru remote debugging):

In Ubuntu:


sudo intel_reg write 0x70280 0xc4842000; \
sudo intel_reg write 0x7029c 0x00940000; \
sudo intel_reg write 0x70290 0x0137027f; \
sudo intel_reg write 0x70288 0x28;



In Win10:


!ed [uc] 0xee070280 0x84000000;!ed [uc] 0xee07029c 0x11000000;!ed [uc] 0xee070290 0x02ff03ff;!ed [uc] 0xee070288 0x40; !ed [uc] 0xee07028c 0x00ff00ff;



I expect to see small glitch images on top of OS and other applications. But in reality, the plane 1 seems also to fail to output. I set the surf base for plane 2 based on the value for plane 1. So the frame buffer of plane 2 should be largely mapped in GTT.


I also modified the surf base of plane 1 and can get the expected result. So the MMIO writes are successful.


Appreciate any clues, thanks!

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