drm/i915: panel: Use atomic PWM API for devs with an external PWM controller

Now that the PWM drivers which we use have been converted to the atomic
PWM API, we can move the i915 panel code over to using the atomic PWM API.

The removes a long standing FIXME and this removes a flicker where
the backlight brightness would jump to 100% when i915 loads even if
using the fastset path.

Note that this commit also simplifies pwm_disable_backlight(), by dropping
the intel_panel_actually_set_backlight(..., 0) call. This call sets the
PWM to 0% duty-cycle. I believe that this call was only present as a
workaround for a bug in the pwm-crc.c driver where it failed to clear the
PWM_OUTPUT_ENABLE bit. This is fixed by an earlier patch in this series.

After the dropping of this workaround, the usleep call, which seems
unnecessary to begin with, has no useful effect anymore, so drop that too.
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-18-hdegoede@redhat.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -28,6 +28,7 @@
 
 #include <linux/async.h>
 #include <linux/i2c.h>
+#include <linux/pwm.h>
 #include <linux/sched/clock.h>
 
 #include <drm/drm_atomic.h>
@@ -223,7 +224,7 @@ struct intel_panel {
 		bool util_pin_active_low;	/* bxt+ */
 		u8 controller;		/* bxt+ only */
 		struct pwm_device *pwm;
-		int pwm_period_ns;
+		struct pwm_state pwm_state;
 
 		/* DPCD backlight */
 		u8 pwmgen_bit_count;

drivers/gpu/drm/i915/display/intel_panel.c

@@ -592,10 +592,10 @@ static u32 bxt_get_backlight(struct intel_connector *connector)
 static u32 pwm_get_backlight(struct intel_connector *connector)
 {
 	struct intel_panel *panel = &connector->panel;
-	int duty_ns;
+	struct pwm_state state;
 
-	duty_ns = pwm_get_duty_cycle(panel->backlight.pwm);
-	return DIV_ROUND_UP(duty_ns * 100, panel->backlight.pwm_period_ns);
+	pwm_get_state(panel->backlight.pwm, &state);
+	return pwm_get_relative_duty_cycle(&state, 100);
 }
 
 static void lpt_set_backlight(const struct drm_connector_state *conn_state, u32 level)
@@ -669,10 +669,9 @@ static void bxt_set_backlight(const struct drm_connector_state *conn_state, u32
 static void pwm_set_backlight(const struct drm_connector_state *conn_state, u32 level)
 {
 	struct intel_panel *panel = &to_intel_connector(conn_state->connector)->panel;
-	int duty_ns = DIV_ROUND_UP(level * panel->backlight.pwm_period_ns, 100);
 
-	pwm_config(panel->backlight.pwm, duty_ns,
-		   panel->backlight.pwm_period_ns);
+	pwm_set_relative_duty_cycle(&panel->backlight.pwm_state, level, 100);
+	pwm_apply_state(panel->backlight.pwm, &panel->backlight.pwm_state);
 }
 
 static void
@@ -841,10 +840,8 @@ static void pwm_disable_backlight(const struct drm_connector_state *old_conn_sta
 	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
 	struct intel_panel *panel = &connector->panel;
 
-	/* Disable the backlight */
-	intel_panel_actually_set_backlight(old_conn_state, 0);
-	usleep_range(2000, 3000);
-	pwm_disable(panel->backlight.pwm);
+	panel->backlight.pwm_state.enabled = false;
+	pwm_apply_state(panel->backlight.pwm, &panel->backlight.pwm_state);
 }
 
 void intel_panel_disable_backlight(const struct drm_connector_state *old_conn_state)
@@ -1176,9 +1173,12 @@ static void pwm_enable_backlight(const struct intel_crtc_state *crtc_state,
 {
 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
 	struct intel_panel *panel = &connector->panel;
+	int level = panel->backlight.level;
 
-	pwm_enable(panel->backlight.pwm);
-	intel_panel_actually_set_backlight(conn_state, panel->backlight.level);
+	level = intel_panel_compute_brightness(connector, level);
+	pwm_set_relative_duty_cycle(&panel->backlight.pwm_state, level, 100);
+	panel->backlight.pwm_state.enabled = true;
+	pwm_apply_state(panel->backlight.pwm, &panel->backlight.pwm_state);
 }
 
 static void __intel_panel_enable_backlight(const struct intel_crtc_state *crtc_state,
@@ -1897,8 +1897,7 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_panel *panel = &connector->panel;
 	const char *desc;
-	u32 level, ns;
-	int retval;
+	u32 level;
 
 	/* Get the right PWM chip for DSI backlight according to VBT */
 	if (dev_priv->vbt.dsi.config->pwm_blc == PPS_BLC_PMIC) {
@@ -1916,35 +1915,28 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 		return -ENODEV;
 	}
 
-	panel->backlight.pwm_period_ns = NSEC_PER_SEC /
-					 get_vbt_pwm_freq(dev_priv);
-
-	/*
-	 * FIXME: pwm_apply_args() should be removed when switching to
-	 * the atomic PWM API.
-	 */
-	pwm_apply_args(panel->backlight.pwm);
-
 	panel->backlight.max = 100; /* 100% */
 	panel->backlight.min = get_backlight_min_vbt(connector);
-	level = intel_panel_compute_brightness(connector, 100);
-	ns = DIV_ROUND_UP(level * panel->backlight.pwm_period_ns, 100);
 
-	retval = pwm_config(panel->backlight.pwm, ns,
-			    panel->backlight.pwm_period_ns);
-	if (retval < 0) {
-		drm_err(&dev_priv->drm, "Failed to configure the pwm chip\n");
-		pwm_put(panel->backlight.pwm);
-		panel->backlight.pwm = NULL;
-		return retval;
-	}
+	if (pwm_is_enabled(panel->backlight.pwm)) {
+		/* PWM is already enabled, use existing settings */
+		pwm_get_state(panel->backlight.pwm, &panel->backlight.pwm_state);
 
-	level = DIV_ROUND_UP(pwm_get_duty_cycle(panel->backlight.pwm) * 100,
-			     panel->backlight.pwm_period_ns);
-	level = intel_panel_compute_brightness(connector, level);
-	panel->backlight.level = clamp(level, panel->backlight.min,
-				       panel->backlight.max);
-	panel->backlight.enabled = panel->backlight.level != 0;
+		level = pwm_get_relative_duty_cycle(&panel->backlight.pwm_state,
+						    100);
+		level = intel_panel_compute_brightness(connector, level);
+		panel->backlight.level = clamp(level, panel->backlight.min,
+					       panel->backlight.max);
+		panel->backlight.enabled = true;
+
+		drm_dbg_kms(&dev_priv->drm, "PWM already enabled at freq %ld, VBT freq %d, level %d\n",
+			    NSEC_PER_SEC / (unsigned long)panel->backlight.pwm_state.period,
+			    get_vbt_pwm_freq(dev_priv), level);
+	} else {
+		/* Set period from VBT frequency, leave other settings at 0. */
+		panel->backlight.pwm_state.period =
+			NSEC_PER_SEC / get_vbt_pwm_freq(dev_priv);
+	}
 
 	drm_info(&dev_priv->drm, "Using %s PWM for LCD backlight control\n",
 		 desc);