Two Intel Graphics Features Get Pulled From Linux 3.17
Linux 3.17-rc1 is still about one week away at least, but already two commits of new functionality were reverted from the Intel DRM driver code for Linux 3.17.
The first revert yesterday to the Linux Git code was in regards to semaphores support for Broadwell. Semaphores support for Broadwell -- a performance-boosting feature -- was part of Intel's big set of changes for this kernel merge window. The DRM pull was just sent in a few days ago but Intel developers decided to end up disabling the semaphores support in a drm-intel-fixes pull request they already submitted to Linus Torvalds.
Semaphores for Broadwell is disabled until further testing has happened. There were still hangs on the Broadwell hardware of Intel engineers and even some slowdowns in performance, so until further testing and optimizations have taken place, this feature is disabled. At least Intel OTC developers have a few months to fix-up the semaphores support before Broadwell hardware is common to the marketplace.
The other Intel feature revert happened by Linus Torvalds. Linus had warned earlier on Friday following the drm-intel-fixes merge, "Hmm. My laptop no longer resumes properly. Or rather, I suspect it resumes, but the screen is black. I will bisect, and I *will* revert if I find the offending commit. I need that laptop for travel next week." Linus ended up finding it was due to enabling the Panel Self Refresh (PSR) feature.
As Linus is traveling with his Sony Vaio Pro 11 next week with its Haswell ULT that's affected by this bug breaking the suspend and resume process, he reverted that feature from being enabled by default. He will only allow it to be re-enabled for the next cycle (Linux 3.18) if it's properly fixed-up by Intel. Panel Self Refresh is a feature found with DisplayPort 1.3 / eDP 1.3. Panel Self Refresh allows for conserving power use by being able to power down the GPU and related circuitry when displaying a static image rather than constantly refreshing the display if the screen contents have been unchanged.
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