[PATCH 4.15 010/146] drm/i915/audio: fix check for av_enc_map overflow

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jani Nikula <jani.nikula@xxxxxxxxx>

commit 72a6d72c2cd03bba7b70117b63dea83d2de88057 upstream.

Turns out -1 >= ARRAY_SIZE() is always true. Move the bounds check where
we know pipe >= 0 and next to the array indexing where it makes most
sense.

Fixes: 9965db26ac05 ("drm/i915: Check for fused or unused pipes")
Fixes: 0b7029b7e43f ("drm/i915: Check for fused or unused pipes")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.10+
Cc: Mika Kahola <mika.kahola@xxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
Reviewed-by: Mika Kahola <mika.kahola@xxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214173840.25360-1-jani.nikula@xxxxxxxxx
(cherry picked from commit cdb3db8542d854bd678d60cd28861b042e191672)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/intel_audio.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_audio.c
+++ b/drivers/gpu/drm/i915/intel_audio.c
@@ -754,11 +754,11 @@ static struct intel_encoder *get_saved_e
 {
 	struct intel_encoder *encoder;
 
-	if (WARN_ON(pipe >= ARRAY_SIZE(dev_priv->av_enc_map)))
-		return NULL;
-
 	/* MST */
 	if (pipe >= 0) {
+		if (WARN_ON(pipe >= ARRAY_SIZE(dev_priv->av_enc_map)))
+			return NULL;
+
 		encoder = dev_priv->av_enc_map[pipe];
 		/*
 		 * when bootup, audio driver may not know it is