From: Arnd Bergmann <a...@arndb.de>

When CONFIG_OF is disabled, building with 'make W=1' produces warnings
about out of bounds array access:

drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array 
bounds of 'struct clk *[4]' [-Werror=array-bounds]

Add an error check before the index is used, which helps with the
warning, as well as any possible other error condition that may be
triggered at runtime.

Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
 drivers/gpu/drm/imx/imx-ldb.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
index dbfe39e2f7f6..1210360cec8a 100644
--- a/drivers/gpu/drm/imx/imx-ldb.c
+++ b/drivers/gpu/drm/imx/imx-ldb.c
@@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder 
*encoder)
        int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
        int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
 
+       if (mux < 0) {
+               dev_warn(ldb->dev,
+                        "%s: invalid mux\n", __func__);
+               return;
+       }
+
        drm_panel_prepare(imx_ldb_ch->panel);
 
        if (dual) {
@@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder 
*encoder,
        int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
        u32 bus_format = imx_ldb_ch->bus_format;
 
+       if (mux < 0) {
+               dev_warn(ldb->dev,
+                        "%s: invalid mux\n", __func__);
+               return;
+       }
+
        if (mode->clock > 170000) {
                dev_warn(ldb->dev,
                         "%s: mode exceeds 170 MHz pixel clock\n", __func__);
-- 
2.29.2

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