[PATCH] drm/dsi: Do the 'msg' check prior to dereferencing it.

[Fabio Estevam]

From: Fabio Estevam <fabio.estevam at freescale.com>

Commit a52879e8d7cb ("drm/dsi: Add message to packet translator") caused the
following Smatch complaint:

drivers/gpu/drm/drm_mipi_dsi.c:328 mipi_dsi_create_packet()
         warn: variable dereferenced before check 'msg' (see line 326)

Do the 'msg' check prior to dereferencing it.

Reported-by: Dan Carpenter <dan.carpenter at oracle.com> 
Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
---
 drivers/gpu/drm/drm_mipi_dsi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index c0644bb..a9812db 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -323,11 +323,13 @@ EXPORT_SYMBOL(mipi_dsi_packet_format_is_long);
 int mipi_dsi_create_packet(struct mipi_dsi_packet *packet,
 			   const struct mipi_dsi_msg *msg)
 {
-	const u8 *tx = msg->tx_buf;
+	const u8 *tx;
 
 	if (!packet || !msg)
 		return -EINVAL;
 
+	tx = msg->tx_buf;
+
 	/* do some minimum sanity checking */
 	if (!mipi_dsi_packet_format_is_short(msg->type) &&
 	    !mipi_dsi_packet_format_is_long(msg->type))
-- 
1.9.1