[PATCH] drm/amd/display: Fix 'panel_cntl' could be null in 'dcn21_set_backlight_level()'

[Srinivasan Shanmugam]

'panel_cntl' structure used control the display panel could be null,
dereferencing it could lead to a null pointer access.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn21/dcn21_hwseq.c:269 
dcn21_set_backlight_level() error: we previously assumed 'panel_cntl' could be 
null (see line 250)

Fixes: 474ac4a875ca ("drm/amd/display: Implement some asic specific abm call 
backs.")
Cc: Yongqiang Sun <yongqiang....@amd.com>
Cc: Anthony Koo <anthony....@amd.com>
Cc: Rodrigo Siqueira <rodrigo.sique...@amd.com>
Cc: Aurabindo Pillai <aurabindo.pil...@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
---
 .../amd/display/dc/hwss/dcn21/dcn21_hwseq.c   | 39 ++++++++++---------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c 
b/drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c
index 8e88dcaf88f5..86b9265f670f 100644
--- a/drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c
@@ -237,34 +237,35 @@ bool dcn21_set_backlight_level(struct pipe_ctx *pipe_ctx,
 {
        struct dc_context *dc = pipe_ctx->stream->ctx;
        struct abm *abm = pipe_ctx->stream_res.abm;
+       u32 otg_inst = pipe_ctx->stream_res.tg->inst;
        struct panel_cntl *panel_cntl = pipe_ctx->stream->link->panel_cntl;
 
+       if (!abm)
+               return false;
+
+       if (!panel_cntl)
+               return false;
+
        if (dc->dc->res_pool->dmcu) {
                dce110_set_backlight_level(pipe_ctx, backlight_pwm_u16_16, 
frame_ramp);
                return true;
        }
 
-       if (abm != NULL) {
-               uint32_t otg_inst = pipe_ctx->stream_res.tg->inst;
-
-               if (abm && panel_cntl) {
-                       if (abm->funcs && abm->funcs->set_pipe_ex) {
-                               abm->funcs->set_pipe_ex(abm,
-                                               otg_inst,
-                                               SET_ABM_PIPE_NORMAL,
-                                               panel_cntl->inst,
-                                               panel_cntl->pwrseq_inst);
-                       } else {
-                                       dmub_abm_set_pipe(abm,
-                                                       otg_inst,
-                                                       SET_ABM_PIPE_NORMAL,
-                                                       panel_cntl->inst,
-                                                       
panel_cntl->pwrseq_inst);
-                       }
-               }
+       if (abm->funcs && abm->funcs->set_pipe_ex) {
+               abm->funcs->set_pipe_ex(abm,
+                                       otg_inst,
+                                       SET_ABM_PIPE_NORMAL,
+                                       panel_cntl->inst,
+                                       panel_cntl->pwrseq_inst);
+       } else {
+               dmub_abm_set_pipe(abm,
+                                 otg_inst,
+                                 SET_ABM_PIPE_NORMAL,
+                                 panel_cntl->inst,
+                                 panel_cntl->pwrseq_inst);
        }
 
-       if (abm && abm->funcs && abm->funcs->set_backlight_level_pwm)
+       if (abm->funcs && abm->funcs->set_backlight_level_pwm)
                abm->funcs->set_backlight_level_pwm(abm, backlight_pwm_u16_16,
                        frame_ramp, 0, panel_cntl->inst);
        else
-- 
2.34.1