media: hantro: Disable multicore support

Avoid exposing equal Hantro video codecs to userspace. Equal video
codecs allow scheduling work between the cores. For that kernel support
is required, which does not yet exist. Until that is implemented avoid
exposing each core separately to userspace so that multicore can be
added in the future without breaking userspace ABI.

This was written with Rockchip RK3588 in mind (which has 4 Hantro H1
cores), but applies to all SoCs.

Signed-off-by: Sebastian Reichel <[e-mail]>
Signed-off-by: Sebastian Fricke <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/platform/verisilicon/hantro_drv.c

···
 	.req_queue = v4l2_m2m_request_queue,
 };
 
+/*
+ * Some SoCs, like RK3588 have multiple identical Hantro cores, but the
+ * kernel is currently missing support for multi-core handling. Exposing
+ * separate devices for each core to userspace is bad, since that does
+ * not allow scheduling tasks properly (and creates ABI). With this workaround
+ * the driver will only probe for the first core and early exit for the other
+ * cores. Once the driver gains multi-core support, the same technique
+ * for detecting the main core can be used to cluster all cores together.
+ */
+static int hantro_disable_multicore(struct hantro_dev *vpu)
+{
+	struct device_node *node = NULL;
+	const char *compatible;
+	bool is_main_core;
+	int ret;
+
+	/* Intentionally ignores the fallback strings */
+	ret = of_property_read_string(vpu->dev->of_node, "compatible", &compatible);
+	if (ret)
+		return ret;
+
+	/* The first compatible and available node found is considered the main core */
+	do {
+		node = of_find_compatible_node(node, NULL, compatible);
+		if (of_device_is_available(node))
+			break;
+	} while (node);
+
+	if (!node)
+		return -EINVAL;
+
+	is_main_core = (vpu->dev->of_node == node);
+
+	of_node_put(node);
+
+	if (!is_main_core) {
+		dev_info(vpu->dev, "missing multi-core support, ignoring this instance\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
 static int hantro_probe(struct platform_device *pdev)
 {
 	const struct of_device_id *match;
···
 
 	match = of_match_node(of_hantro_match, pdev->dev.of_node);
 	vpu->variant = match->data;
+
+	ret = hantro_disable_multicore(vpu);
+	if (ret)
+		return ret;
 
 	/*
 	 * Support for nxp,imx8mq-vpu is kept for backwards compatibility