[PATCH v4 1/9] drm/mediatek: dp: Cache EDID for eDP panel

[AngeloGioacchino Del Regno]

Since eDP panels are not removable it is safe to cache the EDID:
this will avoid a relatively long read transaction at every PM
resume that is unnecessary only in the "special" case of eDP,
hence speeding it up a little, as from now on, as resume operation,
we will perform only link training.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg at gmail.com>
Tested-by: Chen-Yu Tsai <wenst at chromium.org>
---
 drivers/gpu/drm/mediatek/mtk_dp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index 64eee77452c0..fdf5b7686884 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -118,6 +118,7 @@ struct mtk_dp {
 	const struct mtk_dp_data *data;
 	struct mtk_dp_info info;
 	struct mtk_dp_train_info train_info;
+	struct edid *edid;
 
 	struct platform_device *phy_dev;
 	struct phy *phy;
@@ -1993,7 +1994,11 @@ static struct edid *mtk_dp_get_edid(struct drm_bridge *bridge,
 		usleep_range(2000, 5000);
 	}
 
-	new_edid = drm_get_edid(connector, &mtk_dp->aux.ddc);
+	/* eDP panels aren't removable, so we can return a cached EDID. */
+	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP && mtk_dp->edid)
+		new_edid = drm_edid_duplicate(mtk_dp->edid);
+	else
+		new_edid = drm_get_edid(connector, &mtk_dp->aux.ddc);
 
 	/*
 	 * Parse capability here to let atomic_get_input_bus_fmts and
@@ -2022,6 +2027,10 @@ static struct edid *mtk_dp_get_edid(struct drm_bridge *bridge,
 		drm_atomic_bridge_chain_post_disable(bridge, connector->state->state);
 	}
 
+	/* If this is an eDP panel and the read EDID is good, cache it for later */
+	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP && !mtk_dp->edid && new_edid)
+		mtk_dp->edid = drm_edid_duplicate(new_edid);
+
 	return new_edid;
 }
 
-- 
2.40.1