[PATCH] drm/i915: avoid division by zero on skl_calc_wrpll_link

[PATCH] drm/i915: avoid division by zero on skl_calc_wrpll_link

[Yang Xiao]

From: Young Xiao <YangX92@hotmail.com>

If for some unexpected reason the registers all read zero it's better
to WARN and return instead of dividing by zero and completely freezing
the machine.

See commit 0e005888b833 ("drm/i915: avoid division by zero on
cnl_calc_wrpll_link") for detail.

Signed-off-by: Young Xiao <YangX92@hotmail.com>
---
 drivers/gpu/drm/i915/intel_ddi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 5186cd7..cfa7d6f 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1360,6 +1360,9 @@ static int skl_calc_wrpll_link(struct drm_i915_private *dev_priv,
 	dco_freq += (((cfgcr1_val & DPLL_CFGCR1_DCO_FRACTION_MASK) >> 9) * 24 *
 		1000) / 0x8000;
 
+	if (WARN_ON(p0 == 0 || p1 == 0 || p2 == 0))
+		return 0;
+
 	return dco_freq / (p0 * p1 * p2 * 5);
 }
 
-- 
2.7.4

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Re: [PATCH] drm/i915: avoid division by zero on skl_calc_wrpll_link

[Jani Nikula]

On Mon, 17 Dec 2018, Yang Xiao <YangX92@hotmail.com> wrote:
> From: Young Xiao <YangX92@hotmail.com>
>
> If for some unexpected reason the registers all read zero it's better
> to WARN and return instead of dividing by zero and completely freezing
> the machine.
>
> See commit 0e005888b833 ("drm/i915: avoid division by zero on
> cnl_calc_wrpll_link") for detail.
>
> Signed-off-by: Young Xiao <YangX92@hotmail.com>

Pushed to drm-intel-next-queued, thanks for the patch.

BR,
Jani.

> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 5186cd7..cfa7d6f 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1360,6 +1360,9 @@ static int skl_calc_wrpll_link(struct drm_i915_private *dev_priv,
>  	dco_freq += (((cfgcr1_val & DPLL_CFGCR1_DCO_FRACTION_MASK) >> 9) * 24 *
>  		1000) / 0x8000;
>  
> +	if (WARN_ON(p0 == 0 || p1 == 0 || p2 == 0))
> +		return 0;
> +
>  	return dco_freq / (p0 * p1 * p2 * 5);
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center
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