[Intel-gfx] Sandy Bridge GPU hangs after mode switch

[Sanchez, AdolfoX]

Hello here are some details about the problem.

-Operative System: QNX

-Symptoms: Aproximately 1 out of 200 video mode switches will cause the CPU to hang during the next 30-60 VSYNC signals after the mode switches.After hang up most motherboards switch power off after 5-10 seconds.

The mode switcher is based on the document Intel OpenSource HD Graphics Programmer's Reference Manual (PRM) Volume 3 Part 2: Display Registers - CPU Registers (SandyBridge), chapter 1.1.2 for Sandy Bridge
https://01.org/linuxgraphics/sites/default/files/documentation/snb_ihd_os_vol3_part2.pdf
Experimentally it has been determined that the problem can occur after switching on the DSPACNTR bit 31.
The problem is reproducible using any display controller, and any video output. It has been tested in different combinations of SandyBridge and IvyBridge platfors, with different chipsets.

Any help would be appreciated.
Regards,
Adolfo
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