Thinkpad T20: DMA and power management

Hello,

With a Thinkpad T20 after applying the fix I posted in
https://bugs.freedesktop.org/show_bug.cgi?id=8662 I noticed following
problems with vertex DMA enabled: Vertex DMA hangs (i.e. no triangle is
painted at all, 3D engine hangs, tested using a simple handmade program
that sends a draw-request for the front-buffer to the DRM) after the
processor entering C3 state or after an suspend-to-ram/resume cycle
(with vanilla 2.6.18 ACPI), independant of C3 usage. The settings used
are "DmaType AGP", "BusType AGP", "AGPMode 2", "ShadowStatus Off".

This looks like a bus mastering problem, especially the C3 state problem
(vertex dma works like a charm with max_cstate=2), but lspci -H1 -vv
still shows the master bit on the graphics card set. Any further ideas
how to track this bug down?

Furthermore, the problem disappears (incurring a performance drop from
380 fps (AGP/VDMA) to 300 fps for gears, standard window size, 16bpp)
when using PCI DMA instead of AGP DMA. (The 300 fps for PCI are
independent of vertex DMA enabled or disabled. AGP with vertex DMA
disabled is also 300 fps), so it might be an agpgart problem (this
computer uses the Intel 440BX chipset and thus the intel_agp driver)

Michael Karcher


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