Since Linux 3.2-rc2 the following two patches have changed the DDC detect and and probe behaviour of the radeon driver: - drm/radeon/kms: always do extended edid probe - drm/radeon/kms: remove useless radeon_ddc_dump()
The first patch makes an EDID header check mandatory during DDC detection/probe. The second patch removes the DDC check during Radeon device setup, that was done before the actual connector detection. The log output of this check confused users with DP, eDP, or DP bridge connectors.
Found regression: (1) The stop of DDC detection for floating connectors, i. e. connectors with improperly wired/terminated i2c bus, of RS690/RS740 family chipsets does not work anymore. (2) HW bugs that result in the DDC being available, but unusable EDID (header) do now lead to connectors silently probed via i2c but not being used. There is no notification to the user (via kernel logs). Even with drm debugging enabled at kernel boot time, there is no information. No chance for a user to identify the root cause of the connector being probed but not being used.
The attached two fixes restore the RS690/RS740 floating connectors quirk, i. e. stop of DDC detection. In addition, the detection of such floating connectors is now more comprehensive: Also floating connectors with a few (<= 8) random byte values other than zero reported during i2c transaction are now properly detected.
During discussion of patch "drm/radeon/kms: remove useless radeon_ddc_dump()" (see http://www.spinics.net/lists/dri-devel/msg15523.html) the proposal was made to include the log information of the removed function radeon_ddc_dump() into function drm_fb_helper_initial_config(). Further investigations showed, that during intial framebuffer configuration the connector (type) specific detect function will be called surrounded by kernel debug log message output. In the here important radeon DVI connector case function radeon_dvi_detect() is called. As this function is anyway touched by the present patch, I decided to move the unusable EDID logging there. Counter radeon_connector-> broken_edid_header_counter will ensure, that kernel logs are not flooded, as it was the case before implementation of extended DDC/EDID probe.
Thomas Reim (2): drm: Improve detection of floating connectors drm/radeon/kms: wrap-up handling of floating connectors and connector unavailability status logging
drivers/gpu/drm/drm_edid.c | 13 ++++++- drivers/gpu/drm/radeon/radeon_connectors.c | 54 +++++++++++++++++++++++----- drivers/gpu/drm/radeon/radeon_i2c.c | 7 +++- drivers/gpu/drm/radeon/radeon_mode.h | 3 ++ 4 files changed, 65 insertions(+), 12 deletions(-)