Otherwise, we might receive a new interrupt before we have time to
ack the first one, eventually missing it.
Without an atomic XCHG operation with mmio space, this patch merely
reduces the window in which we can miss an interrupt (especially when
you consider how heavyweight the I915_READ/I915_WRITE operations are).
Notice that, before clearing a port-sourced interrupt in the IIR, the
corresponding interrupt source status in the PORT_HOTPLUG_STAT must be
cleared.
Spotted by Bob Beckett <robert.beckett@intel.com>.
v2:
- Add warning to commit message and comments to the code as per Chris
Wilson's request.
- Imre Deak pointed out that the pipe underrun flag might not be signaled
in IIR, so do not make valleyview_pipestat_irq_handler depend on it.
v3: Improve the source code comment.
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
************************************************************
* 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
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