[PATCH 32/42] drm/mediatek: mtk_crtc: Dynamically find suitable CRTC DMA device

[AngeloGioacchino Del Regno]

Now that the vblank and config components are being dynamically
selected, the only hardcoded strategy that is left is selecting
a DMA device for a CRTC that is being created.

In order to support pipelines including an embedded multimedia
controller (like MDP3) chained with the display controller and
pipelines chaining multiple display controllers together, stop
assuming that the first component in the pipeline is suited to
do DMA operations and implement support to dynamically find not
only a suitable DMA device, but also the best one.

This finds the first device that provides DMA and the first one
that is also behind an IOMMU.

The criteria for selecting the best device is to prefer a DMA
device behind an IOMMU; if not found, the first DMA capable
one is selected instead.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
---
 drivers/gpu/drm/mediatek/mtk_crtc.c | 68 ++++++++++++++++++++++++-----
 1 file changed, 56 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
index ee23a50cf4d1..3f70d11270e9 100644
--- a/drivers/gpu/drm/mediatek/mtk_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
@@ -1131,6 +1131,60 @@ struct device *mtk_crtc_dma_dev_get(struct drm_crtc *crtc)
 	return mtk_crtc->dma_dev;
 }
 
+static int mtk_crtc_find_suitable_dma_dev(struct mtk_drm_private *priv,
+					  struct mtk_crtc *mtk_crtc,
+					  const struct mtk_drm_path_definition *path)
+{
+	struct mtk_ddp_comp *dma_comp = NULL, *dma_comp_mmu = NULL;
+	int i;
+
+	for (i = 0; i < mtk_crtc->ddp_comp_nr; i++) {
+		const struct mtk_drm_comp_definition *cdef = path[i].comp;
+		struct mtk_ddp_comp *comp;
+
+		comp = mtk_ddp_comp_find_by_id(&priv->hlist,
+					       cdef->type, cdef->inst_id);
+		if (!comp)
+			continue;
+
+		/*
+		 * Check if this is a legacy OVL_ADAPTOR component and, if so, this
+		 * has to forcefully be the DMA device for this CRTC: assign it to
+		 * dma_comp_mmu to force that.
+		 */
+		if (comp->type == MTK_DISP_OVL_ADAPTOR) {
+			dma_comp_mmu = comp;
+			break;
+		}
+
+		if (!comp->dev || !comp->dev->of_node)
+			continue;
+
+		/* Find the first device provides DMA... */
+		if (!dma_comp) {
+			if (of_property_present(comp->dev->of_node, "#dma-cells"))
+				dma_comp = comp;
+		}
+
+		/* ...and check if that device is also behind an IOMMU */
+		if (!of_property_present(comp->dev->of_node, "iommus"))
+			continue;
+
+		/* If a device behind IOMMU is found, this is the best outcome */
+		dma_comp_mmu = comp;
+		break;
+	}
+
+	if (dma_comp_mmu)
+		mtk_crtc->dma_dev = mtk_ddp_comp_dma_dev_get(dma_comp_mmu);
+	else if (dma_comp)
+		mtk_crtc->dma_dev = mtk_ddp_comp_dma_dev_get(dma_comp);
+	else
+		return -EINVAL;
+
+	return 0;
+}
+
 int mtk_crtc_create(struct drm_device *drm_dev,
 		    enum mtk_crtc_path path_sel, int priv_data_index,
 		    const struct mtk_drm_route *conn_routes,
@@ -1139,7 +1193,6 @@ int mtk_crtc_create(struct drm_device *drm_dev,
 	struct mtk_drm_private *priv = drm_dev->dev_private;
 	const struct mtk_drm_path_definition *output_path;
 	struct device *dev = drm_dev->dev;
-	struct mtk_ddp_comp *dma_comp;
 	struct mtk_crtc *mtk_crtc;
 	unsigned int num_comp_planes = 0;
 	unsigned int max_comp_stages = 0;
@@ -1309,20 +1362,11 @@ int mtk_crtc_create(struct drm_device *drm_dev,
 	dev_dbg(dev, "Found %u layers composed by maximum of %u stage(s) each.\n",
 		mtk_crtc->hwlayer_nr, max_comp_stages);
 
-	/*
-	 * Default to use the first component as the dma dev.
-	 * In the case of ovl_adaptor sub driver, it needs to use the
-	 * dma_dev_get function to get representative dma dev.
-	 */
-	dma_comp = mtk_ddp_comp_find_by_id(&priv->hlist,
-					   output_path->comp[0].type,
-					   output_path->comp[0].inst_id);
-	if (dma_comp == NULL) {
+	ret = mtk_crtc_find_suitable_dma_dev(priv, mtk_crtc, output_path);
+	if (ret) {
 		dev_err(dev, "Could not find appropriate DMA device!\n");
 		return -EINVAL;
 	}
-
-	mtk_crtc->dma_dev = mtk_ddp_comp_dma_dev_get(dma_comp);
 	dev_dbg(dev, "Using DMA device %pOF\n", mtk_crtc->dma_dev->of_node);
 
 	ret = mtk_crtc_init(drm_dev, mtk_crtc, crtc_i);
-- 
2.54.0