releases/3.14.12/drm-i915-avoid-div-by-zero-when-pixel_multiplier-is-zero.patch

From 2b85886a5457f5c5dbcd32edbd4e6bba0f4e8678 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Mon, 9 Jun 2014 16:20:46 +0300
Subject: drm/i915: Avoid div-by-zero when pixel_multiplier is zero
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

commit 2b85886a5457f5c5dbcd32edbd4e6bba0f4e8678 upstream.

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
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/intel_sdvo.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1383,7 +1383,9 @@ static void intel_sdvo_get_config(struct
 			 >> 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);