[PATCH] drm/amd/display: Remove unnecessary NULL check in dcn20_set_input_transfer_func

[Harry Wentland]

On 2024-04-23 09:59, Srinivasan Shanmugam wrote:
> This commit removes an unnecessary NULL check in the
> `dcn20_set_input_transfer_func` function in the `dcn20_hwseq.c` file.
> The variable `tf` is assigned the address of
> `plane_state->in_transfer_func` unconditionally, so it can never be
> `NULL`. Therefore, the check `if (tf == NULL)` is unnecessary and has
> been removed.
> 
> The plane_state->in_transfer_func itself cannot be NULL because it's a
> structure, not a pointer. When we do tf =
> &plane_state->in_transfer_func;, we're getting the address of that
> structure, which will always be valid as long as plane_state itself is
> not NULL.
> 
> we've already checked if plane_state is NULL with the line if (dpp_base
> == NULL || plane_state == NULL) return false;. So, if the code execution
> gets to the point where tf = &plane_state->in_transfer_func; is called,
> plane_state is guaranteed to be not NULL, and therefore tf will also not
> be NULL.
> 
> drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c
>     1094 bool dcn20_set_input_transfer_func(struct dc *dc,
>     1095                                 struct pipe_ctx *pipe_ctx,
>     1096                                 const struct dc_plane_state *plane_state)
>     1097 {
>     1098         struct dce_hwseq *hws = dc->hwseq;
>     1099         struct dpp *dpp_base = pipe_ctx->plane_res.dpp;
>     1100         const struct dc_transfer_func *tf = NULL;
>                                                 ^^^^^^^^^ This assignment is not necessary now.
> 
>     1101         bool result = true;
>     1102         bool use_degamma_ram = false;
>     1103 
>     1104         if (dpp_base == NULL || plane_state == NULL)
>     1105                 return false;
>     1106 
>     1107         hws->funcs.set_shaper_3dlut(pipe_ctx, plane_state);
>     1108         hws->funcs.set_blend_lut(pipe_ctx, plane_state);
>     1109 
>     1110         tf = &plane_state->in_transfer_func;
>                  ^^^^^
> Before there was an if statement but now tf is assigned unconditionally
> 
>     1111 
> --> 1112         if (tf == NULL) {
>                  ^^^^^^^^^^^^^^^^^
> so these conditions are impossible.
> 
>     1113                 dpp_base->funcs->dpp_set_degamma(dpp_base,
>     1114                                 IPP_DEGAMMA_MODE_BYPASS);
>     1115                 return true;
>     1116         }
>     1117 
>     1118         if (tf->type == TF_TYPE_HWPWL || tf->type == TF_TYPE_DISTRIBUTED_POINTS)
>     1119                 use_degamma_ram = true;
>     1120 
>     1121         if (use_degamma_ram == true) {
>     1122                 if (tf->type == TF_TYPE_HWPWL)
>     1123                         dpp_base->funcs->dpp_program_degamma_pwl(dpp_base,
> 
> Fixes the below Smatch static checker warning:
> drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c:1112 dcn20_set_input_transfer_func() warn: address of 'plane_state->in_transfer_func' is non-NULL
> 
> Fixes: 285a7054bf81 ("drm/amd/display: Remove plane and stream pointers from dc scratch")
> Cc: Wenjing Liu <wenjing.liu at amd.com>
> Cc: Tom Chung <chiahsuan.chung at amd.com>
> Cc: Alvin Lee <alvin.lee2 at amd.com>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
> Cc: Roman Li <roman.li at amd.com>
> Cc: Qingqing Zhuo <Qingqing.Zhuo at amd.com>
> Cc: Aurabindo Pillai <aurabindo.pillai at amd.com>
> Cc: Harry Wentland <harry.wentland at amd.com>
> Suggested-by: Dan Carpenter <dan.carpenter at linaro.org>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>

Previously plane_state->in_transfer_func was a pointer but that was
changed recently. Looks like this place was missed.

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

> ---
>  drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c b/drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c
> index b60ba2a110f7..58fbdd535068 100644
> --- a/drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c
> +++ b/drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c
> @@ -1109,12 +1109,6 @@ bool dcn20_set_input_transfer_func(struct dc *dc,
>  
>  	tf = &plane_state->in_transfer_func;
>  
> -	if (tf == NULL) {
> -		dpp_base->funcs->dpp_set_degamma(dpp_base,
> -				IPP_DEGAMMA_MODE_BYPASS);
> -		return true;
> -	}
> -
>  	if (tf->type == TF_TYPE_HWPWL || tf->type == TF_TYPE_DISTRIBUTED_POINTS)
>  		use_degamma_ram = true;
>