From 746d024c3211813946b319411aeb2b47767f8fb0 Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Thu, 15 Mar 2018 17:19:57 +0100
Subject: [PATCH] gpu: ipu-v3: prg: avoid possible array underflow
Git-commit: 746d024c3211813946b319411aeb2b47767f8fb0
Patch-mainline: v4.16-rc7
References: bsc#1051510

gcc-8 reports that we access an array with a negative index
in an error case:

Drivers/gpu/ipu-v3/ipu-prg.c: In function 'ipu_prg_channel_disable':
drivers/gpu/ipu-v3/ipu-prg.c:252:43: error: array subscript -22 is below array bounds of 'struct ipu_prg_channel[3]' [-Werror=array-bounds]

This moves the range check in front of the first time that
variable gets used.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/ipu-v3/ipu-prg.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/gpu/ipu-v3/ipu-prg.c
+++ b/drivers/gpu/ipu-v3/ipu-prg.c
@@ -251,10 +251,14 @@ void ipu_prg_channel_disable(struct ipuv
 {
 	int prg_chan = ipu_prg_ipu_to_prg_chan(ipu_chan->num);
 	struct ipu_prg *prg = ipu_chan->ipu->prg_priv;
-	struct ipu_prg_channel *chan = &prg->chan[prg_chan];
+	struct ipu_prg_channel *chan;
 	u32 val;
 
-	if (!chan->enabled || prg_chan < 0)
+	if (prg_chan < 0)
+		return;
+
+	chan = &prg->chan[prg_chan];
+	if (!chan->enabled)
 		return;
 
 	clk_prepare_enable(prg->clk_ipg);
@@ -281,13 +285,15 @@ int ipu_prg_channel_configure(struct ipu
 {
 	int prg_chan = ipu_prg_ipu_to_prg_chan(ipu_chan->num);
 	struct ipu_prg *prg = ipu_chan->ipu->prg_priv;
-	struct ipu_prg_channel *chan = &prg->chan[prg_chan];
+	struct ipu_prg_channel *chan;
 	u32 val;
 	int ret;
 
 	if (prg_chan < 0)
 		return prg_chan;
 
+	chan = &prg->chan[prg_chan];
+
 	if (chan->enabled) {
 		ipu_pre_update(prg->pres[chan->used_pre], *eba);
 		return 0;