Intel Pulls In ShadowFB Support For KMS
Written by Michael Larabel in Intel on 8 September 2010 at 10:28 AM EDT. 11 Comments
While Ubuntu 10.10 will have no i8xx driver fix for those with this vintage Intel hardware that's been plagued with stability problems and other issues since Intel introduced their Linux kernel mode-setting and GEM driver, there is now a workaround upstream for this issue. Originally the plan was to add back user-space mode-setting support to the Intel X.Org driver that would not use the Graphics Execution Manager (GEM) and this code-path could be enabled by i8xx customers to workaround the cache coherency issues while losing KMS support, but a new workaround was devised.

Adding back UMS support to the xf86-video-intel driver would add around 50,000 lines of code back to the DDX driver and it would likely receive little in the way of new development and testing, so a much less invasive solution was devised by Intel's Chris Wilson. This new workaround, which we talked about recently, was adding shadow frame-buffer support to Intel KMS. In other words, kernel mode-setting still could be used by i8xx owners, but a ShadowFB-like method would be used for acceleration, which basically means no GPU acceleration at all.

The few hundred line commit adding shadow frame-buffer support to the Intel driver was merged to master early this morning. When the Shadow option is enabled from the xorg.conf, no GPU acceleration will be used but rather it will be leveraged on the CPU and system memory. No X-Video or 3D acceleration can be used with this driver, but now at least there is X-Video still possible via the hardware overlay. But because GEM isn't being tapped, the incoherency bugs for i8xx should be worked around thereby giving you a stable system.

The commit showing this shadow support being merged into the mainline xf86-video-intel driver can be found on Git. This support will be found in the xf86-video-intel 2.13 driver, which should be released in a few weeks.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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