[Intel-gfx] [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero
Jani Nikula
jani.nikula at linux.intel.com
Tue Jun 10 18:41:29 CEST 2014
On Tue, 10 Jun 2014, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Mon, Jun 09, 2014 at 04:20:46PM +0300, ville.syrjala at linux.intel.com wrote:
>> From: Ville Syrjälä <ville.syrjala at 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 at 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 at vger.kernel.org> # 3.13+
>> Tested-by: Tim Richardson <tim at tim-richardson.net>
>> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Pushed to -fixes, thanks for the patch and review.
BR,
Jani.
>
>> ---
>> 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 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);
>> --
>> 1.8.5.5
>>
>> _______________________________________________
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>> Intel-gfx at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
> _______________________________________________
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--
Jani Nikula, Intel Open Source Technology Center
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