drm/bridge: waveshare-dsi: Fix signedness bug

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@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202603060341.hNj0pl9L-lkp@intel.com/
Fixes: fca11428425e9 ("drm/bridge: waveshare-dsi: Add support for 1..4 DSI data lanes")
Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://patch.msgid.link/20260307033245.71666-1-ethantidmore06@gmail.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/drivers/gpu/drm/bridge/waveshare-dsi.c b/drivers/gpu/drm/bridge/waveshare-dsi.c
index 0497c7ecbc7a55f883145ecec9fcfd64caacb73a..32d40414adb9ff84ffb2fac1aebee9f1d01d6618 100644 (file)
--- 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);