drm/amd/display: Guard against setting dispclk low when active

[Why]
We should never apply a minimum dispclk value while in prepare_bandwidth
or while displays are active. This is always an optimization for when
all displays are disabled.

[How]
Defer dispclk optimization until safe_to_lower = true and display_count
reaches 0.

Since 0 has a special value in this logic (ie. no dispclk required)
we also need adjust the logic that clamps it for the actual request
to PMFW.

Reviewed-by: Gabe Teeger <gabe.teeger@amd.com>
Reviewed-by: Leo Chen <leo.chen@amd.com>
Reviewed-by: Syed Hassan <syed.hassan@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Nicholas Kazlauskas

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c

@@ -467,14 +467,19 @@ void dcn35_update_clocks(struct clk_mgr *clk_mgr_base,
 		update_dppclk = true;
 	}
 
-	if (should_set_clock(safe_to_lower, new_clocks->dispclk_khz, clk_mgr_base->clks.dispclk_khz)) {
+	if (should_set_clock(safe_to_lower, new_clocks->dispclk_khz, clk_mgr_base->clks.dispclk_khz) &&
+	    (new_clocks->dispclk_khz > 0 || (safe_to_lower && display_count == 0))) {
+		int requested_dispclk_khz = new_clocks->dispclk_khz;
+
 		dcn35_disable_otg_wa(clk_mgr_base, context, safe_to_lower, true);
 
-		if (dc->debug.min_disp_clk_khz > 0 && new_clocks->dispclk_khz < dc->debug.min_disp_clk_khz)
-			new_clocks->dispclk_khz = dc->debug.min_disp_clk_khz;
+		/* Clamp the requested clock to PMFW based on their limit. */
+		if (dc->debug.min_disp_clk_khz > 0 && requested_dispclk_khz < dc->debug.min_disp_clk_khz)
+			requested_dispclk_khz = dc->debug.min_disp_clk_khz;
 
+		dcn35_smu_set_dispclk(clk_mgr, requested_dispclk_khz);
 		clk_mgr_base->clks.dispclk_khz = new_clocks->dispclk_khz;
-		dcn35_smu_set_dispclk(clk_mgr, clk_mgr_base->clks.dispclk_khz);
+
 		dcn35_disable_otg_wa(clk_mgr_base, context, safe_to_lower, false);
 
 		update_dispclk = true;