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During suspend, Linus found that his machine would hang for 3 seconds, and identified that intel_ring_buffer_wait() was the culprit: "Because from looking at the code, I get the notion that "intel_read_status_page()" may not be exact. But what happens if that inexact value matches our cached ring->actual_head, so we never even try to read the exact case? Does it _stay_ inexact for arbitrarily long times? If so, we might wait for the ring to empty forever (well, until the timeout - the behavior I see), even though the ring really _is_ empty." As the reported HEAD position is only updated every time it crosses a 64k boundary, whilst draining the ring it is indeed likely to remain one value. If that value matches the last known HEAD position, we never read the true value from the register and so trigger a timeout. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
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* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
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The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html