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[1050/1094] drm/i915: Avoid div-by-zero when pixel_multiplier is zero

Message ID 1413889294-31328-1051-git-send-email-dheerajx.s.jamwal@intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Dheeraj Jamwal Oct. 21, 2014, 11 a.m. UTC 
From: Ville Syrjälä <ville.syrjala@linux.intel.com>

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>
(cherry picked from commit 2b85886a5457f5c5dbcd32edbd4e6bba0f4e8678)

Signed-off-by: Dheeraj Jamwal <dheerajx.s.jamwal@intel.com>
---
 drivers/gpu/drm/i915/intel_sdvo.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
diff mbox

Patch

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 6a4d5bc..20375cc 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1385,7 +1385,9 @@  static void intel_sdvo_get_config(struct intel_encoder *encoder,
 			 >> SDVO_PORT_MULTIPLY_SHIFT) + 1;
 	}
 
-	dotclock = pipe_config->port_clock / pipe_config->pixel_multiplier;
+	dotclock = pipe_config->port_clock;
+	if (pipe_config->pixel_multiplier)
+		dotclock /= pipe_config->pixel_multiplier;
 
 	if (HAS_PCH_SPLIT(dev))
 		ironlake_check_encoder_dotclock(pipe_config, dotclock);