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ab2aa47e4b
GEN8 removes the GT FIFO which we've all come to know and love. Instead it offers a wider range of optimized registers which always keep a shadowed copy, and are fed to the GPU when it wakes. How this is implemented in hardware is still somewhat of a mystery. As far as I can tell, the basic design is as follows: If the register is not optimized, you must use the old forcewake mechanism to bring the GT out of sleep. [1] If register is in the optimized list the write will signal that the GT should begin to come out of whatever sleep state it is in. While the GT is coming out of sleep, the requested write will be stored in an intermediate shadow register. Do to the fact that the implementation details are not clear, I see several risks: 1. Order is not preserved as it is with GT FIFO. If we issue multiple writes to optimized registers, where order matters, we may need to serialize it with forcewake. 2. The optimized registers have only 1 shadowed slot, meaning if we issue multiple writes to the same register, and those values need to reach the GPU in order, forcewake will be required. [1] We could implement a SW queue the way the GT FIFO used to work if desired. NOTE: Compile tested only until we get real silicon. v2: - Use a default case to make future platforms also work. - Get rid of IS_BROADWELL since that's not yet defined, but we want to MMIO as soon as possible. v3: Apply suggestions from Mika's review: - s/optimized/shadowed/ - invert the logic of the helper so that it does what it says (the code itself was correct, just confusing to read). v4: - Squash in lost break. Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1) Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
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