[PATCH 0/2] RFC: Potential improvements in edid detection timings

[Eugeni Dodonov <eugeni@dodonov.net>]

From: Eugeni Dodonov <eugeni.dodonov@intel.com>

This is the the forth iteration of potential fixes for slow edid detection
issues over non-existent outputs
(https://bugs.freedesktop.org/show_bug.cgi?id=41059) - the previous versions
were posted to the bug and were used mostly for debugging the problem.

After investigation, I came to think on two different ways to fix the issue:
in PATCH1, I added a check for the return value of i2c_transfer - and, if it
is -ENXIO, we give up on further attempts as the bus is not there. A
drawback to this approach is that it affects all the devices out there which
use drm_get_edid.  From my testing, the -ENXIO gave no false positives, but
I haven't tested it on non-Intel cards.

The second patch does a similar procedure within the i915 driver. It adds a
new function - intel_drm_get_valid_edid - which attempts to do a simple i2c
transfer over the bus prior to calling drm_get_edid. In case such transfer
fails with -ENXIO, it is a signal that the bus is not there, so we shouldn't
waste any time trying to communicate with it further.

Note that those patches provide lots of dmesg pollution - I just wanted to
send them out to get an overall feedback on the proposed approach.

Eugeni Dodonov (2):
  Give up on edid retries when i2c tells us that bus is not there
  Check if the bus is valid prior to discovering edid.

 drivers/gpu/drm/drm_edid.c         |    5 +++++
 drivers/gpu/drm/i915/intel_dp.c    |    4 ++--
 drivers/gpu/drm/i915/intel_drv.h   |    2 ++
 drivers/gpu/drm/i915/intel_hdmi.c  |    4 ++--
 drivers/gpu/drm/i915/intel_i2c.c   |   33 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lvds.c  |    2 +-
 drivers/gpu/drm/i915/intel_modes.c |    2 +-
 drivers/gpu/drm/i915/intel_sdvo.c  |    4 ++--
 8 files changed, 48 insertions(+), 8 deletions(-)

-- 
1.7.6.3