[PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Ethan Tidmore]

The function drm_of_get_data_lanes_count_ep() returns negative error
codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
0) is always impossible.

Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
ret, check for error, and then assign dsi->lanes to ret.

Detected by Smatch:
drivers/gpu/drm/bridge/waveshare-dsi.c:70 ws_bridge_attach_dsi() warn:
unsigned 'dsi->lanes' is never less than zero.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202603060341.hNj0pl9L-lkp@xxxxxxxxx/
Fixes: fca11428425e9 ("drm/bridge: waveshare-dsi: Add support for 1..4 DSI data lanes")
Signed-off-by: Ethan Tidmore <ethantidmore06@xxxxxxxxx>
---
 drivers/gpu/drm/bridge/waveshare-dsi.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/waveshare-dsi.c b/drivers/gpu/drm/bridge/waveshare-dsi.c
index 0497c7ecbc7a..32d40414adb9 100644
--- a/drivers/gpu/drm/bridge/waveshare-dsi.c
+++ b/drivers/gpu/drm/bridge/waveshare-dsi.c
@@ -66,11 +66,13 @@ static int ws_bridge_attach_dsi(struct ws_bridge *ws)
 	dsi->mode_flags = MIPI_DSI_MODE_VIDEO_HSE | MIPI_DSI_MODE_VIDEO |
 			  MIPI_DSI_CLOCK_NON_CONTINUOUS;
 	dsi->format = MIPI_DSI_FMT_RGB888;
-	dsi->lanes = drm_of_get_data_lanes_count_ep(dev->of_node, 0, 0, 1, 4);
-	if (dsi->lanes < 0) {
+	ret = drm_of_get_data_lanes_count_ep(dev->of_node, 0, 0, 1, 4);
+	if (ret < 0) {
 		dev_warn(dev, "Invalid or missing DSI lane count %d, falling back to 2 lanes\n",
-			 dsi->lanes);
+			 ret);
 		dsi->lanes = 2;	/* Old DT backward compatibility */
+	} else {
+		dsi->lanes = ret;
 	}
 
 	ret = devm_mipi_dsi_attach(dev, dsi);
-- 
2.53.0