drm/vc4: kms: Take old state core clock rate into account

During a commit, the core clock, which feeds the HVS, needs to run at
a minimum of 500MHz.

While doing that commit, we can also change the mode to one that
requires a higher core clock, so we take the core clock rate associated
to that new state into account for that boost.

However, the old state also needs to be taken into account if it
requires a core clock higher that the new one and our 500MHz limit,
since it's still live in hardware at the beginning of our commit.

Fixes: 16e101051f ("drm/vc4: Increase the core clock based on HVS load")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220331143744.777652-2-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -386,9 +386,10 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 	}
 
 	if (vc4->hvs->hvs5) {
+		unsigned long state_rate = max(old_hvs_state->core_clock_rate,
+					       new_hvs_state->core_clock_rate);
 		unsigned long core_rate = max_t(unsigned long,
-						500000000,
-						new_hvs_state->core_clock_rate);
+						500000000, state_rate);
 
 		drm_dbg(dev, "Raising the core clock at %lu Hz\n", core_rate);