drm/panel-edp: Take advantage of wait_hpd_asserted() in struct drm_dp_aux

Let's add support for being able to read the HPD pin even if it's
hooked directly to the controller. This will allow us to get more
accurate delays also lets us take away the waiting in the AUX transfer
functions of the eDP controller drivers.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220614145327.v4.2.Icea616f57331fbaa3d48c529f300c9a8ebd37fb5@changeid

drivers/gpu/drm/panel/panel-edp.c

@@ -418,6 +418,11 @@ static int panel_edp_get_hpd_gpio(struct device *dev, struct panel_edp *p)
 	return 0;
 }
 
+static bool panel_edp_can_read_hpd(struct panel_edp *p)
+{
+	return !p->no_hpd && (p->hpd_gpio || (p->aux && p->aux->wait_hpd_asserted));
+}
+
 static int panel_edp_prepare_once(struct panel_edp *p)
 {
 	struct device *dev = p->base.dev;
@@ -442,17 +447,21 @@ static int panel_edp_prepare_once(struct panel_edp *p)
 	if (delay)
 		msleep(delay);
 
-	if (p->hpd_gpio) {
+	if (panel_edp_can_read_hpd(p)) {
 		if (p->desc->delay.hpd_absent)
 			hpd_wait_us = p->desc->delay.hpd_absent * 1000UL;
 		else
 			hpd_wait_us = 2000000;
 
-		err = readx_poll_timeout(gpiod_get_value_cansleep, p->hpd_gpio,
-					 hpd_asserted, hpd_asserted,
-					 1000, hpd_wait_us);
+		if (p->hpd_gpio) {
+			err = readx_poll_timeout(gpiod_get_value_cansleep,
+						 p->hpd_gpio, hpd_asserted,
+						 hpd_asserted, 1000, hpd_wait_us);
 			if (hpd_asserted < 0)
 				err = hpd_asserted;
+		} else {
+			err = p->aux->wait_hpd_asserted(p->aux, hpd_wait_us);
+		}
 
 		if (err) {
 			if (err != -ETIMEDOUT)
@@ -533,18 +542,22 @@ static int panel_edp_enable(struct drm_panel *panel)
 	/*
 	 * If there is a "prepare_to_enable" delay then that's supposed to be
 	 * the delay from HPD going high until we can turn the backlight on.
-	 * However, we can only count this if HPD is handled by the panel
-	 * driver, not if it goes to a dedicated pin on the controller.
+	 * However, we can only count this if HPD is readable by the panel
+	 * driver.
+	 *
 	 * If we aren't handling the HPD pin ourselves then the best we
 	 * can do is assume that HPD went high immediately before we were
-	 * called (and link training took zero time).
+	 * called (and link training took zero time). Note that "no-hpd"
+	 * actually counts as handling HPD ourselves since we're doing the
+	 * worst case delay (in prepare) ourselves.
 	 *
 	 * NOTE: if we ever end up in this "if" statement then we're
 	 * guaranteed that the panel_edp_wait() call below will do no delay.
 	 * It already handles that case, though, so we don't need any special
 	 * code for it.
 	 */
-	if (p->desc->delay.prepare_to_enable && !p->hpd_gpio && !p->no_hpd)
+	if (p->desc->delay.prepare_to_enable &&
+	    !panel_edp_can_read_hpd(p) && !p->no_hpd)
 		delay = max(delay, p->desc->delay.prepare_to_enable);
 
 	if (delay)