From 83482ca3b4fe7312bf3d1f25c7a4e9ff66585eab Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Thu, 5 Oct 2017 14:08:26 +0200
Subject: [PATCH] drm/i915: avoid potential uninitialized variable use
Git-commit: 83482ca3b4fe7312bf3d1f25c7a4e9ff66585eab
Patch-mainline: v4.15-rc1
References: FATE#322643 bsc#1055900

One of the recent changes introduced a warning about
undefined behavior in the sanity checking:

Drivers/gpu/drm/i915/intel_ddi.c: In function 'intel_ddi_hdmi_level':
drivers/gpu/drm/i915/intel_ddi.c:654:6: error: 'n_hdmi_entries' may be used uninitialized in this function [-Werror=maybe-uninitialized]

It seems that the new cnl specific get_buf_trans functions
can return uninitialized data if the voltage level is set
to an unexpected value. This changes the code to always return
'1' in that error case, which seems like the safest choice
as we use one less than the number as an array index later on.

Fixes: cc9cabfdec38 ("drm/i915/cnl: Move voltage check into ddi buf trans functions.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[danvet: shut up gcc comment added.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171005120835.437022-1-arnd@arndb.de
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/intel_ddi.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -602,8 +602,10 @@ cnl_get_buf_trans_hdmi(struct drm_i915_p
 	} else if (voltage == VOLTAGE_INFO_1_05V) {
 		*n_entries = ARRAY_SIZE(cnl_ddi_translations_hdmi_1_05V);
 		return cnl_ddi_translations_hdmi_1_05V;
-	} else
+	} else {
+		*n_entries = 1; /* shut up gcc */
 		MISSING_CASE(voltage);
+	}
 	return NULL;
 }
 
@@ -621,8 +623,10 @@ cnl_get_buf_trans_dp(struct drm_i915_pri
 	} else if (voltage == VOLTAGE_INFO_1_05V) {
 		*n_entries = ARRAY_SIZE(cnl_ddi_translations_dp_1_05V);
 		return cnl_ddi_translations_dp_1_05V;
-	} else
+	} else {
+		*n_entries = 1; /* shut up gcc */
 		MISSING_CASE(voltage);
+	}
 	return NULL;
 }
 
@@ -641,8 +645,10 @@ cnl_get_buf_trans_edp(struct drm_i915_pr
 		} else if (voltage == VOLTAGE_INFO_1_05V) {
 			*n_entries = ARRAY_SIZE(cnl_ddi_translations_edp_1_05V);
 			return cnl_ddi_translations_edp_1_05V;
-		} else
+		} else {
+			*n_entries = 1; /* shut up gcc */
 			MISSING_CASE(voltage);
+		}
 		return NULL;
 	} else {
 		return cnl_get_buf_trans_dp(dev_priv, n_entries);