| From | Kamal Mostafa <> | Subject | [PATCH 3.13 143/198] drm/i915: Avoid div-by-zero when pixel_multiplier is zero | Date | Tue, 15 Jul 2014 14:30:13 -0700 |
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3.13.11.5 -stable review patch. If anyone has any objections, please let me know.
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From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <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: Kamal Mostafa <kamal@canonical.com> --- drivers/gpu/drm/i915/intel_sdvo.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c index a583e8f..9528239 100644 --- a/drivers/gpu/drm/i915/intel_sdvo.c +++ b/drivers/gpu/drm/i915/intel_sdvo.c @@ -1364,7 +1364,9 @@ 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); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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