Commits
Ville Syrjälä committed 2b85886a545
drm/i915: Avoid div-by-zero when pixel_multiplier is zero
On certain platforms pixel_multiplier is read out in
.get_pipe_config(), but it also gets used to calculate the
pixel clock in intel_sdvo_get_config(). If the pipe is disable
but some SDVO outputs are active, we may end up dividing by zero
in intel_sdvo_get_config().
To avoid the problem simply check for zero pixel_multiplier and skip
the division. Another attempt at fixing this involved populating
pixel_multiplier to 1 even for disabled pipes, but that triggered a
WARN because SDVO_CMD_GET_CLOCK_RATE_MULT command failed and thus
encoder_pixel_multiplier was left at zero and didn't match
pipe_config->pixel_multiplier.
The "divide by pixel_multiplier" operation got introduced here:
commit 18442d08786472c63a0a80c27f92b033dffc26de
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date: Fri Sep 13 16:00:08 2013 +0300
drm/i915: Fix port_clock and adjusted_mode.clock readout all over
and it has caused a regression on certain machines since they would
hit the div-by-zero during resume.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76520
Cc: <stable@vger.kernel.org> # 3.13+
Tested-by: Tim Richardson <tim@tim-richardson.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>