Bspec and the code suggests that the interrupt signaled by IIR[7,5]
(DISPLAY_PIPE_A/B_VBLANK) is a first level IRQ flag for the second
level PIPEA/BSTAT[2] (Start of Vertical Blank) interrupt. Measuring
the relative timings of when IIR[7] and PIPEASTAT[1,2] get set and
checking the effect of unmasking different pipestat and IIR events
shows that this isn't so:
First, ISR/IIR[7] gets set independently of PIPEASTAT[18] (Start of
Vertical Blank Enable) or any other pipestat enable bit, so it isn't
a first level IRQ bit showing the state of PIPEASTAT[2], but is
connected directly to the timing generator.
Second, setting only PIPEASTAT[18] and leaving all other pipestat events
disabled, IIR[6] (DISPLAY_PIPE_A_EVENT) gets set close to the moment when
PIPEASTAT[2] gets set, so the former is a first level interrupt flag for
the latter. The bspec is rather unclear about this, but I also assume
that IIR[6] signals all pipestat A events, except PIPEASTAT[31] (FIFO
Under-run Status).
Third, IIR[7] is set close to the moment when PIPEASTAT[1] (Framestart
Interrupt) gets set, in the mode I used about 12usec after PIPEASTAT[2]
and IIR[6] gets set. This means the IIR[7] isn't marking the start of
vblank, but rather signals the framestart event.
Based on the above, we don't need to unmask IIR[7] when waiting for
start of vblank events, but we can rely on IIR[6] being always unmasked,
which will signal when PIPEASTAT[2] gets set. Doing this will also get
rid of the overhead of getting an interrupt and servicing IIR[7], which
is atm raised always some time after IIR[6]/PIPEASTAT[2] is raised.
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
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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