VGA registers live inside the power well on HSW, so in order to write
the VGA MSR register we need the power well to be on.
We really must write to the register to properly clear the
VGA_MSR_MEM_EN enable bit, even if all VGA registers get zeroed when
the power well is down. It seems that the implicit zeroing done by
the power well is not enough to propagate the VGA_MSR_MEM_EN bit to
whomever is actually responsible for the memory decode ranges.
If we leave VGA memory decode enabled, and then turn off the power well,
all VGA memory reads will return zeroes. But if we first disable VGA
memory deocde and then turn off the power well, VGA memory reads
return all ones, indicating that the access wasn't claimed by anyone.
For the vga arbiter to function correctly the IGD must not claim the
VGA memory accesses.
Previously we were doing the VGA_MSR register access while the power well
was excplicitly powered up during driver init. But ever since
commit 6e1b4fdad5
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date: Thu Sep 5 20:40:52 2013 +0300
drm/i915: Delay disabling of VGA memory until vgacon->fbcon handoff is done
we delay the VGA memory disable until fbcon has initialized, and so
there's a possibility that the power well got turned off during the
fbcon modeset. Also vgacon_save_screen() will need the power well to be
on to be able to read the VGA memory.
So immediately after enabling the power well during init grab a refence
for VGA purposes, and after all the VGA handling is done, release it.
v2: Add intel_display_power_put() for the num_pipes==0 case
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Fix up the patch wiggle screw-up that I've done and which
Paulo catched. Also polish spelling in the patch headline.]
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
ce35255032