media: rkvdec: Disable multicore support

Similarly to what is done in Hantro, avoid exposing equal 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 currently applies only to RK3588 which has 2 equal VDPU381 decoders,
but will be applied for all SoC supported by rkvdec that has multiple DTS
nodes with the same compatible.

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

Author: cazou

drivers/media/platform/rockchip/rkvdec/rkvdec.c

@@ -1269,6 +1269,49 @@ static void rkvdec_watchdog_func(struct work_struct *work)
 	}
 }
 
+/*
+ * Some SoCs, like RK3588 have multiple identical VDPU 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 first core can be used to cluster all cores together.
+ */
+static int rkvdec_disable_multicore(struct rkvdec_dev *rkvdec)
+{
+	struct device_node *node = NULL;
+	const char *compatible;
+	bool is_first_core;
+	int ret;
+
+	/* Intentionally ignores the fallback strings */
+	ret = of_property_read_string(rkvdec->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_first_core = (rkvdec->dev->of_node == node);
+
+	of_node_put(node);
+
+	if (!is_first_core) {
+		dev_info(rkvdec->dev, "missing multi-core support, ignoring this instance\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
 static const struct rkvdec_variant_ops rk3399_variant_ops = {
 	.irq_handler = rk3399_irq_handler,
 };
@@ -1332,6 +1375,10 @@ static int rkvdec_probe(struct platform_device *pdev)
 	mutex_init(&rkvdec->vdev_lock);
 	INIT_DELAYED_WORK(&rkvdec->watchdog_work, rkvdec_watchdog_func);
 
+	ret = rkvdec_disable_multicore(rkvdec);
+	if (ret)
+		return ret;
+
 	ret = devm_clk_bulk_get_all_enabled(&pdev->dev, &rkvdec->clocks);
 	if (ret < 0)
 		return ret;