* [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero
@ 2014-06-09 13:20 ville.syrjala
2014-06-10 7:12 ` Daniel Vetter
0 siblings, 1 reply; 3+ messages in thread
From: ville.syrjala @ 2014-06-09 13:20 UTC (permalink / raw)
To: intel-gfx; +Cc: stable
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>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.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 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
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero
2014-06-09 13:20 [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero ville.syrjala
@ 2014-06-10 7:12 ` Daniel Vetter
2014-06-10 16:41 ` [Intel-gfx] " Jani Nikula
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Vetter @ 2014-06-10 7:12 UTC (permalink / raw)
To: ville.syrjala; +Cc: intel-gfx, stable
On Mon, Jun 09, 2014 at 04:20:46PM +0300, ville.syrjala@linux.intel.com wrote:
> 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>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
> 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
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Intel-gfx] [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero
2014-06-10 7:12 ` Daniel Vetter
@ 2014-06-10 16:41 ` Jani Nikula
0 siblings, 0 replies; 3+ messages in thread
From: Jani Nikula @ 2014-06-10 16:41 UTC (permalink / raw)
To: Daniel Vetter, ville.syrjala; +Cc: intel-gfx, stable
On Tue, 10 Jun 2014, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Mon, Jun 09, 2014 at 04:20:46PM +0300, ville.syrjala@linux.intel.com wrote:
>> 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>
>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Reviewed-by: Daniel Vetter <daniel.vetter@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
>>
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@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
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Jani Nikula, Intel Open Source Technology Center
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-06-09 13:20 [PATCH] drm/i915: Avoid div-by-zero when pixel_multiplier is zero ville.syrjala
2014-06-10 7:12 ` Daniel Vetter
2014-06-10 16:41 ` [Intel-gfx] " Jani Nikula
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