4 files changed, 133 insertions, 0 deletions

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index c17193544268..6284538a8184 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -178,4 +178,14 @@ config VIRTIO_DMA_SHARED_BUFFER
 	 This option adds a flavor of dma buffers that are backed by
 	 virtio resources.
 
+config VIRTIO_DEBUG
+	bool "Debug facilities"
+	depends on VIRTIO
+	help
+	  Enable this to expose debug facilities over debugfs.
+	  This allows to debug features, to see what features the device
+	  advertises and to set filter for features used by driver.
+
+	  If unsure, say N.
+
 endif # VIRTIO_MENU
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 73ace62af440..58b2b0489fc9 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -13,3 +13,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
 obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
 obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
 obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
+obj-$(CONFIG_VIRTIO_DEBUG) += virtio_debug.o
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 9510c551dce8..b968b2aa5f4d 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -274,6 +274,9 @@ static int virtio_dev_probe(struct device *_d)
 	else
 		dev->features = driver_features_legacy & device_features;
 
+	/* When debugging, user may filter some features by hand. */
+	virtio_debug_device_filter_features(dev);
+
 	/* Transport features always preserved to pass to finalize_features. */
 	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
 		if (device_features & (1ULL << i))
@@ -465,6 +468,8 @@ int register_virtio_device(struct virtio_device *dev)
 	/* Acknowledge that we've seen the device. */
 	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
 
+	virtio_debug_device_init(dev);
+
 	/*
 	 * device_add() causes the bus infrastructure to look for a matching
 	 * driver.
@@ -496,6 +501,7 @@ void unregister_virtio_device(struct virtio_device *dev)
 	int index = dev->index; /* save for after device release */
 
 	device_unregister(&dev->dev);
+	virtio_debug_device_exit(dev);
 	ida_free(&virtio_index_ida, index);
 }
 EXPORT_SYMBOL_GPL(unregister_virtio_device);
@@ -590,11 +596,13 @@ static int virtio_init(void)
 {
 	if (bus_register(&virtio_bus) != 0)
 		panic("virtio bus registration failed");
+	virtio_debug_init();
 	return 0;
 }
 
 static void __exit virtio_exit(void)
 {
+	virtio_debug_exit();
 	bus_unregister(&virtio_bus);
 	ida_destroy(&virtio_index_ida);
 }
diff --git a/drivers/virtio/virtio_debug.c b/drivers/virtio/virtio_debug.c
new file mode 100644
index 000000000000..95c8fc7705bb
--- /dev/null
+++ b/drivers/virtio/virtio_debug.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/debugfs.h>
+
+static struct dentry *virtio_debugfs_dir;
+
+static int virtio_debug_device_features_show(struct seq_file *s, void *data)
+{
+	struct virtio_device *dev = s->private;
+	u64 device_features;
+	unsigned int i;
+
+	device_features = dev->config->get_features(dev);
+	for (i = 0; i < BITS_PER_LONG_LONG; i++) {
+		if (device_features & (1ULL << i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_device_features);
+
+static int virtio_debug_filter_features_show(struct seq_file *s, void *data)
+{
+	struct virtio_device *dev = s->private;
+	unsigned int i;
+
+	for (i = 0; i < BITS_PER_LONG_LONG; i++) {
+		if (dev->debugfs_filter_features & (1ULL << i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_filter_features);
+
+static int virtio_debug_filter_features_clear(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val == 1)
+		dev->debugfs_filter_features = 0;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_features_clear_fops, NULL,
+			 virtio_debug_filter_features_clear, "%llu\n");
+
+static int virtio_debug_filter_feature_add(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= BITS_PER_LONG_LONG)
+		return -EINVAL;
+	dev->debugfs_filter_features |= BIT_ULL_MASK(val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_add_fops, NULL,
+			 virtio_debug_filter_feature_add, "%llu\n");
+
+static int virtio_debug_filter_feature_del(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= BITS_PER_LONG_LONG)
+		return -EINVAL;
+	dev->debugfs_filter_features &= ~BIT_ULL_MASK(val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_del_fops, NULL,
+			 virtio_debug_filter_feature_del, "%llu\n");
+
+void virtio_debug_device_init(struct virtio_device *dev)
+{
+	dev->debugfs_dir = debugfs_create_dir(dev_name(&dev->dev),
+					      virtio_debugfs_dir);
+	debugfs_create_file("device_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_device_features_fops);
+	debugfs_create_file("filter_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_fops);
+	debugfs_create_file("filter_features_clear", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_clear_fops);
+	debugfs_create_file("filter_feature_add", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_add_fops);
+	debugfs_create_file("filter_feature_del", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_del_fops);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_init);
+
+void virtio_debug_device_filter_features(struct virtio_device *dev)
+{
+	dev->features &= ~dev->debugfs_filter_features;
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_filter_features);
+
+void virtio_debug_device_exit(struct virtio_device *dev)
+{
+	debugfs_remove_recursive(dev->debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_exit);
+
+void virtio_debug_init(void)
+{
+	virtio_debugfs_dir = debugfs_create_dir("virtio", NULL);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_init);
+
+void virtio_debug_exit(void)
+{
+	debugfs_remove_recursive(virtio_debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_exit);