[radeon-alex:drm-next-4.18-wip 43/120] drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_optc.c:127 get_start_vline() warn: unsigned 'vertical_line_start' is never less than zero.

[kbuild test robot]

tree:   git://people.freedesktop.org/~agd5f/linux.git drm-next-4.18-wip
head:   5d404d3139a4624892a12683240abfae931ee849
commit: 2852a36199784540a872f42fa6dc7d8d51eee0d8 [43/120] drm/amd/display: Add vline IRQ programming for DCN

smatch warnings:
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_optc.c:127 get_start_vline() warn: unsigned 'vertical_line_start' is never less than zero.

vim +/vertical_line_start +127 drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_optc.c

    95	
    96	static uint32_t get_start_vline(struct timing_generator *optc, const struct dc_crtc_timing *dc_crtc_timing)
    97	{
    98		struct dc_crtc_timing patched_crtc_timing;
    99		uint32_t vesa_sync_start;
   100		uint32_t asic_blank_end;
   101		uint32_t interlace_factor;
   102		uint32_t vertical_line_start;
   103	
   104		patched_crtc_timing = *dc_crtc_timing;
   105		optc1_apply_front_porch_workaround(optc, &patched_crtc_timing);
   106	
   107		vesa_sync_start = patched_crtc_timing.h_addressable +
   108				patched_crtc_timing.h_border_right +
   109				patched_crtc_timing.h_front_porch;
   110	
   111		asic_blank_end = patched_crtc_timing.h_total -
   112				vesa_sync_start -
   113				patched_crtc_timing.h_border_left;
   114	
   115		interlace_factor = patched_crtc_timing.flags.INTERLACE ? 2 : 1;
   116	
   117		vesa_sync_start = patched_crtc_timing.v_addressable +
   118				patched_crtc_timing.v_border_bottom +
   119				patched_crtc_timing.v_front_porch;
   120	
   121		asic_blank_end = (patched_crtc_timing.v_total -
   122				vesa_sync_start -
   123				patched_crtc_timing.v_border_top)
   124				* interlace_factor;
   125	
   126		vertical_line_start = asic_blank_end - optc->dlg_otg_param.vstartup_start + 1;
 > 127		if (vertical_line_start < 0) {
   128			ASSERT(0);
   129			vertical_line_start = 0;
   130		}
   131	
   132		return vertical_line_start;
   133	}
   134	

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