[PATCH] drm/i915/dp: prevent potential div-by-zero

[Nikita Zhandarovich]

drm_dp_dsc_sink_max_slice_count() may return 0 if something goes
wrong on the part of the DSC sink and its DPCD register. This null
value may be later used as a divisor in intel_dsc_compute_params(),
which will lead to an error.
In the unlikely event that this issue occurs, fix it by testing the
return value of drm_dp_dsc_sink_max_slice_count() against zero.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: a4a157777c80 ("drm/i915/dp: Compute DSC pipe config in atomic check")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 62cbab7402e9..c1825f8f885c 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1533,6 +1533,11 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 		pipe_config->dsc.slice_count =
 			drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
 							true);
+		if (!pipe_config->dsc.slice_count) {
+			drm_dbg_kms(&dev_priv->drm, "Unsupported Slice Count %d\n",
+				    pipe_config->dsc.slice_count);
+			return -EINVAL;
+		}
 	} else {
 		u16 dsc_max_output_bpp = 0;
 		u8 dsc_dp_slice_count;
-- 
2.25.1