[PATCH v2 8/8] drm/mediatek: dp: Add support for embedded DisplayPort aux-bus

[AngeloGioacchino Del Regno]

For the eDP case we can support using aux-bus on MediaTek DP: this
gives us the possibility to declare our panel as generic "panel-edp"
which will automatically configure the timings and available modes
via the EDID that we read from it.

To do this, move the panel parsing at the end of the probe function
so that the hardware is initialized beforehand and also power it on
as, when we populate the aux-bus, the panel driver will trigger an
EDID read as panel detection.

**** CUT ****
Also, since the DP IP will always trigger a HPD interrupt at this
stage, it was necessary to add a new `bridge_attached` member to
the mtk_dp structure to make sure that `drm_helper_hpd_irq_event()`
will not be called before the bridge gets actually attached, or
otherwise we will get a NULL pointer KP due to mtk_dp->bridge.dev
being uninitialized.
**** CUT ****

Last but not least, since now the AUX transfers can happen in the
separated aux-bus, it was necessary to add an exclusion for the
cable_plugged_in check in `mtk_dp_aux_transfer()` and the easiest
way to do this is to simply ignore checking that when the bridge
type is eDP.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
---
 drivers/gpu/drm/mediatek/mtk_dp.c | 56 +++++++++++++++++++++++++------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index 62d53c4b3feb..f62ef24db67d 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -4,6 +4,7 @@
  * Copyright (c) 2022 BayLibre
  */
 
+#include <drm/display/drm_dp_aux_bus.h>
 #include <drm/display/drm_dp.h>
 #include <drm/display/drm_dp_helper.h>
 #include <drm/drm_atomic_helper.h>
@@ -2041,7 +2042,8 @@ static ssize_t mtk_dp_aux_transfer(struct drm_dp_aux *mtk_aux,
 
 	mtk_dp = container_of(mtk_aux, struct mtk_dp, aux);
 
-	if (!mtk_dp->train_info.cable_plugged_in) {
+	if (mtk_dp->bridge.type != DRM_MODE_CONNECTOR_eDP &&
+	    !mtk_dp->train_info.cable_plugged_in) {
 		ret = -EAGAIN;
 		goto err;
 	}
@@ -2153,6 +2155,11 @@ static int mtk_dp_bridge_attach(struct drm_bridge *bridge,
 	enable_irq(mtk_dp->irq);
 	mtk_dp_hwirq_enable(mtk_dp, true);
 
+	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP /* && panel_on_aux_bus() */) {
+		mtk_dp->train_info.cable_plugged_in = true;
+		drm_helper_hpd_irq_event(mtk_dp->drm_dev);
+	}
+
 	return 0;
 
 err_bridge_attach:
@@ -2482,6 +2489,20 @@ static int mtk_dp_register_audio_driver(struct device *dev)
 	return PTR_ERR_OR_ZERO(mtk_dp->audio_pdev);
 }
 
+static int mtk_dp_edp_link_panel(struct drm_dp_aux *mtk_aux)
+{
+	struct mtk_dp *mtk_dp = container_of(mtk_aux, struct mtk_dp, aux);
+	struct device *dev = mtk_aux->dev;
+	struct drm_bridge *panel_aux_bridge;
+
+	panel_aux_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
+	if (IS_ERR(panel_aux_bridge))
+		return PTR_ERR(panel_aux_bridge);
+
+	mtk_dp->next_bridge = panel_aux_bridge;
+	return 0;
+}
+
 static int mtk_dp_probe(struct platform_device *pdev)
 {
 	struct mtk_dp *mtk_dp;
@@ -2500,21 +2521,14 @@ static int mtk_dp_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, mtk_dp->irq,
 				     "failed to request dp irq resource\n");
 
-	mtk_dp->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
-	if (IS_ERR(mtk_dp->next_bridge) &&
-	    PTR_ERR(mtk_dp->next_bridge) == -ENODEV)
-		mtk_dp->next_bridge = NULL;
-	else if (IS_ERR(mtk_dp->next_bridge))
-		return dev_err_probe(dev, PTR_ERR(mtk_dp->next_bridge),
-				     "Failed to get bridge\n");
-
 	ret = mtk_dp_dt_parse(mtk_dp, pdev);
 	if (ret)
 		return dev_err_probe(dev, ret, "Failed to parse dt\n");
 
-	drm_dp_aux_init(&mtk_dp->aux);
 	mtk_dp->aux.name = "aux_mtk_dp";
+	mtk_dp->aux.dev = dev;
 	mtk_dp->aux.transfer = mtk_dp_aux_transfer;
+	drm_dp_aux_init(&mtk_dp->aux);
 
 	spin_lock_init(&mtk_dp->irq_thread_lock);
 
@@ -2570,6 +2584,28 @@ static int mtk_dp_probe(struct platform_device *pdev)
 	mtk_dp->need_debounce = true;
 	timer_setup(&mtk_dp->debounce_timer, mtk_dp_debounce_timer, 0);
 
+	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP) {
+		/* Need to power on HW because aux-bus will read EDID */
+		mtk_dp_aux_panel_poweron(mtk_dp, true);
+
+		ret = devm_of_dp_aux_populate_bus(&mtk_dp->aux, NULL);
+
+		/* Power off AUX and panel now as detection is done. */
+		mtk_dp_aux_panel_poweron(mtk_dp, false);
+
+		/* We ignore -ENODEV error, as the panel may not be on aux-bus */
+		if (ret && ret != -ENODEV)
+			return ret;
+
+		/*
+		 * Here we don't ignore any error, as if there's no panel to
+		 * link, eDP is not configured correctly and will be unusable.
+		 */
+		ret = mtk_dp_edp_link_panel(&mtk_dp->aux);
+		if (ret)
+			return ret;
+	}
+
 	pm_runtime_enable(dev);
 	pm_runtime_get_sync(dev);
 
-- 
2.40.0