drm/i915: avoid division by zero on skl_calc_wrpll_link

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>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/SG2PR01MB2169F6E95BC8BB5E29477042ADBC0@SG2PR01MB2169.apcprd01.prod.exchangelabs.com

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index fdf57f451b72b8fa8bf13e244b1f453811cbff35..2d6ed990a2327d2e1cad08517ec125e7f55b1c12 100644 (file)
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1296,6 +1296,9 @@ 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);
 }