drm/vc4: Add logging and comments

The HVS core clock isn't really obvious, so let's add a bunch more
comments and some logging for easier debugging.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220225143534.405820-12-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -390,8 +390,15 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 						500000000,
 						new_hvs_state->core_clock_rate);
 
+		drm_dbg(dev, "Raising the core clock at %lu Hz\n", core_rate);
+
+		/*
+		 * Do a temporary request on the core clock during the
+		 * modeset.
+		 */
 		clk_set_min_rate(hvs->core_clk, core_rate);
 	}
+
 	drm_atomic_helper_commit_modeset_disables(dev, state);
 
 	vc4_ctm_commit(vc4, state);
@@ -417,6 +424,10 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 		drm_dbg(dev, "Running the core clock at %lu Hz\n",
 			new_hvs_state->core_clock_rate);
 
+		/*
+		 * Request a clock rate based on the current HVS
+		 * requirements.
+		 */
 		clk_set_min_rate(hvs->core_clk, new_hvs_state->core_clock_rate);
 	}
 }