[bug report] drm/amd/display: If one stream full updates, full update all planes

[Kazlauskas, Nicholas]

On 4/23/19 10:10 AM, Dan Carpenter wrote:
> Hello David Francis,
> 
> This is a semi-automatic email about new static checker warnings.
> 
> The patch c238bfe0be9e: "drm/amd/display: If one stream full updates,
> full update all planes" from Mar 29, 2019, leads to the following
> Smatch complaint:
> 
>      drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:1492 det_surface_update()
>      warn: variable dereferenced before check 'u->surface' (see line 1467)
> 
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c
>    1466	
>    1467		if (u->surface->force_full_update) {
>                      ^^^^^^^^^^^^
> The patch adds a new dereference
> 
>    1468			update_flags->bits.full_update = 1;
>    1469			return UPDATE_TYPE_FULL;
>    1470		}
>    1471	
>    1472		type = get_plane_info_update_type(u);
>    1473		elevate_update_type(&overall_type, type);
>    1474	
>    1475		type = get_scaling_info_update_type(u);
>    1476		elevate_update_type(&overall_type, type);
>    1477	
>    1478		if (u->in_transfer_func)
>    1479			update_flags->bits.in_transfer_func_change = 1;
>    1480	
>    1481		if (u->input_csc_color_matrix)
>    1482			update_flags->bits.input_csc_change = 1;
>    1483	
>    1484		if (u->coeff_reduction_factor)
>    1485			update_flags->bits.coeff_reduction_change = 1;
>    1486	
>    1487		if (u->gamma) {
>    1488			enum surface_pixel_format format = SURFACE_PIXEL_FORMAT_GRPH_BEGIN;
>    1489	
>    1490			if (u->plane_info)
>    1491				format = u->plane_info->format;
>    1492			else if (u->surface)
>                                   ^^^^^^^^^^
> But the old code assumed it could be NULL

This looks like a check that could probably be dropped. This function 
shouldn't be called with a u->surface = NULL - there's even that other 
deference at the top of the function with &u->surface->update_flags;

Nicholas Kazlauskas

> 
>    1493				format = u->surface->format;
>    1494	
> 
> regards,
> dan carpenter
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