[PATCH] drm/i915: Avoid div-by-zero in clock calculation funcs

[PATCH] drm/i915: Avoid div-by-zero in clock calculation funcs

[ville.syrjala]

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

Check that the N and P dividers don't cause a divide by zero.

This shouldn't happen under normal circumstances, but can
happen eg. under simulation.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0bb3d6d..4bedaf9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -329,6 +329,8 @@ static void vlv_clock(int refclk, intel_clock_t *clock)
 {
 	clock->m = clock->m1 * clock->m2;
 	clock->p = clock->p1 * clock->p2;
+	if (WARN_ON(clock->n == 0 || clock->p == 0))
+		return;
 	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
 	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
 }
@@ -430,6 +432,8 @@ static void pineview_clock(int refclk, intel_clock_t *clock)
 {
 	clock->m = clock->m2 + 2;
 	clock->p = clock->p1 * clock->p2;
+	if (WARN_ON(clock->n == 0 || clock->p == 0))
+		return;
 	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
 	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
 }
@@ -443,6 +447,8 @@ static void i9xx_clock(int refclk, intel_clock_t *clock)
 {
 	clock->m = i9xx_dpll_compute_m(clock);
 	clock->p = clock->p1 * clock->p2;
+	if (WARN_ON(clock->n + 2 == 0 || clock->p == 0))
+		return;
 	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
 	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
 }
-- 
1.8.3.2

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Re: [PATCH] drm/i915: Avoid div-by-zero in clock calculation funcs

[Jesse Barnes]

On Mon,  2 Dec 2013 19:00:45 +0200
ville.syrjala@linux.intel.com wrote:

> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Check that the N and P dividers don't cause a divide by zero.
> 
> This shouldn't happen under normal circumstances, but can
> happen eg. under simulation.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 0bb3d6d..4bedaf9 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -329,6 +329,8 @@ static void vlv_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = clock->m1 * clock->m2;
>  	clock->p = clock->p1 * clock->p2;
> +	if (WARN_ON(clock->n == 0 || clock->p == 0))
> +		return;
>  	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
>  	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }
> @@ -430,6 +432,8 @@ static void pineview_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = clock->m2 + 2;
>  	clock->p = clock->p1 * clock->p2;
> +	if (WARN_ON(clock->n == 0 || clock->p == 0))
> +		return;
>  	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
>  	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }
> @@ -443,6 +447,8 @@ static void i9xx_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = i9xx_dpll_compute_m(clock);
>  	clock->p = clock->p1 * clock->p2;
> +	if (WARN_ON(clock->n + 2 == 0 || clock->p == 0))
> +		return;
>  	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
>  	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center
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