[RFC PATCH 11/17] drm/vkms: Add and remove VKMS instances via configfs

["José Expósito" <jose.exposito89@gmail.com>]

Allow to create, enable, disable and destroy VKMS instances using
configfs.

For the moment, add one primary plane, one CRC, one encoder and one
connector until we add support to configure them via configfs.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 Documentation/gpu/vkms.rst           |  32 +++++
 drivers/gpu/drm/vkms/Kconfig         |   1 +
 drivers/gpu/drm/vkms/Makefile        |   3 +-
 drivers/gpu/drm/vkms/vkms_configfs.c | 198 +++++++++++++++++++++++++++
 drivers/gpu/drm/vkms/vkms_configfs.h |   9 ++
 drivers/gpu/drm/vkms/vkms_drv.c      |  19 ++-
 drivers/gpu/drm/vkms/vkms_drv.h      |   4 +
 7 files changed, 262 insertions(+), 4 deletions(-)
 create mode 100644 drivers/gpu/drm/vkms/vkms_configfs.c
 create mode 100644 drivers/gpu/drm/vkms/vkms_configfs.h

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index ba04ac7c2167..9895a9ae76f4 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -51,6 +51,38 @@ To disable the driver, use ::
 
   sudo modprobe -r vkms
 
+Configuring With Configfs
+=========================
+
+It is possible to create and configure multiple VKMS instances via configfs.
+
+Start by mounting configfs and loading VKMS::
+
+  sudo mount -t configfs none /config
+  sudo modprobe vkms
+
+Once VKMS is loaded, ``/config/vkms`` is created automatically. Each directory
+under ``/config/vkms`` represents a VKMS instance, create a new one::
+
+  sudo mkdir /config/vkms/my-vkms
+
+By default, the instance is disabled::
+
+  cat /config/vkms/my-vkms/enabled
+  0
+
+Once you are done configuring the VKMS instance, enable it::
+
+  echo "1" | sudo tee /config/vkms/my-vkms/enabled
+
+Finally, you can remove the VKMS instance disabling it::
+
+  echo "0" | sudo tee /config/vkms/my-vkms/enabled
+
+Or removing the top level directory::
+
+  sudo rmdir /config/vkms/my-vkms
+
 Testing With IGT
 ================
 
diff --git a/drivers/gpu/drm/vkms/Kconfig b/drivers/gpu/drm/vkms/Kconfig
index b9ecdebecb0b..de218b21a579 100644
--- a/drivers/gpu/drm/vkms/Kconfig
+++ b/drivers/gpu/drm/vkms/Kconfig
@@ -6,6 +6,7 @@ config DRM_VKMS
 	select DRM_KMS_HELPER
 	select DRM_GEM_SHMEM_HELPER
 	select CRC32
+	select CONFIGFS_FS
 	default n
 	help
 	  Virtual Kernel Mode-Setting (VKMS) is used for testing or for
diff --git a/drivers/gpu/drm/vkms/Makefile b/drivers/gpu/drm/vkms/Makefile
index b371b5d70ee3..81c257d37689 100644
--- a/drivers/gpu/drm/vkms/Makefile
+++ b/drivers/gpu/drm/vkms/Makefile
@@ -7,6 +7,7 @@ vkms-y := \
 	vkms_crtc.o \
 	vkms_composer.o \
 	vkms_writeback.o \
-	vkms_config.o
+	vkms_config.o \
+	vkms_configfs.o
 
 obj-$(CONFIG_DRM_VKMS) += vkms.o
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
new file mode 100644
index 000000000000..3f25295f7788
--- /dev/null
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -0,0 +1,198 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/configfs.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+
+#include "vkms_drv.h"
+#include "vkms_config.h"
+#include "vkms_configfs.h"
+
+/* To avoid registering configfs more than once or unregistering on error */
+static bool is_configfs_registered;
+
+/**
+ * struct vkms_configfs - Configfs configuration for a VKMS device
+ *
+ * @vkms_config: Configuration of the VKMS device
+ * @device_group: Top level configuration group that represents a VKMS device.
+ * Initialized when a new directory is created under "/config/vkms/"
+ * @lock: Lock used to project concurrent access to the configuration attributes
+ * @enabled: Protected by @lock. The device is created or destroyed when this
+ * option changes
+ */
+struct vkms_configfs {
+	struct vkms_config *vkms_config;
+	struct config_group device_group;
+
+	/* protected by @lock */
+	struct mutex lock;
+	bool enabled;
+};
+
+#define config_item_to_vkms_configfs(item) \
+	container_of(to_config_group(item), struct vkms_configfs, device_group)
+
+static ssize_t device_enabled_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs *configfs = config_item_to_vkms_configfs(item);
+
+	return sprintf(page, "%d\n", configfs->enabled);
+}
+
+static ssize_t device_enabled_store(struct config_item *item, const char *page,
+				    size_t count)
+{
+	struct vkms_configfs *configfs = config_item_to_vkms_configfs(item);
+	bool enabled;
+	int ret = 0;
+
+	if (kstrtobool(page, &enabled))
+		return -EINVAL;
+
+	mutex_lock(&configfs->lock);
+
+	if (!configfs->enabled && enabled)
+		ret = vkms_create(configfs->vkms_config);
+	else if (configfs->enabled && !enabled)
+		vkms_destroy(configfs->vkms_config);
+
+	if (ret)
+		goto err_unlock;
+
+	configfs->enabled = enabled;
+
+	mutex_unlock(&configfs->lock);
+
+	return (ssize_t)count;
+
+err_unlock:
+	mutex_unlock(&configfs->lock);
+	return ret;
+}
+
+CONFIGFS_ATTR(device_, enabled);
+
+static struct configfs_attribute *device_group_attrs[] = {
+	&device_attr_enabled,
+	NULL,
+};
+
+static const struct config_item_type device_group_type = {
+	.ct_attrs = device_group_attrs,
+	.ct_owner = THIS_MODULE,
+};
+
+static struct config_group *make_device_group(struct config_group *group,
+					      const char *name)
+{
+	struct vkms_configfs *configfs;
+	struct vkms_config_crtc *crtc_cfg = NULL;
+	struct vkms_config_encoder *encoder_cfg = NULL;
+	struct vkms_config_connector *connector_cfg = NULL;
+	char *config_name;
+	int ret;
+
+	if (strcmp(name, DEFAULT_DEVICE_NAME) == 0)
+		return ERR_PTR(-EINVAL);
+
+	configfs = kzalloc(sizeof(*configfs), GFP_KERNEL);
+	if (!configfs)
+		return ERR_PTR(-ENOMEM);
+
+	config_group_init_type_name(&configfs->device_group, name, &device_group_type);
+	mutex_init(&configfs->lock);
+
+	config_name = config_item_name(&configfs->device_group.cg_item);
+	configfs->vkms_config = vkms_config_create(config_name);
+	if (IS_ERR(configfs->vkms_config)) {
+		ret = PTR_ERR(configfs->vkms_config);
+		goto err_kfree;
+	}
+
+	crtc_cfg = vkms_config_add_crtc(configfs->vkms_config, false, false);
+	if (IS_ERR(crtc_cfg)) {
+		ret = PTR_ERR(crtc_cfg);
+		goto err_kfree;
+	}
+
+	encoder_cfg = vkms_config_add_encoder(configfs->vkms_config, BIT(0));
+	if (IS_ERR(encoder_cfg)) {
+		ret = PTR_ERR(encoder_cfg);
+		goto err_kfree;
+	}
+
+	connector_cfg = vkms_config_add_connector(configfs->vkms_config, BIT(0),
+						  connector_status_connected);
+	if (IS_ERR(connector_cfg)) {
+		ret = PTR_ERR(connector_cfg);
+		goto err_kfree;
+	}
+
+	return &configfs->device_group;
+
+err_kfree:
+	kfree(configfs);
+	kfree(crtc_cfg);
+	kfree(encoder_cfg);
+	kfree(connector_cfg);
+	return ERR_PTR(ret);
+}
+
+static void drop_device_group(struct config_group *group,
+			      struct config_item *item)
+{
+	struct vkms_configfs *configfs = config_item_to_vkms_configfs(item);
+
+	mutex_lock(&configfs->lock);
+
+	if (configfs->enabled)
+		vkms_destroy(configfs->vkms_config);
+
+	kfree(configfs->vkms_config);
+
+	mutex_unlock(&configfs->lock);
+
+	kfree(configfs);
+}
+
+static struct configfs_group_operations device_group_ops = {
+	.make_group = &make_device_group,
+	.drop_item = &drop_device_group,
+};
+
+static struct config_item_type vkms_type = {
+	.ct_group_ops = &device_group_ops,
+	.ct_owner = THIS_MODULE,
+};
+
+static struct configfs_subsystem vkms_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_name = "vkms",
+			.ci_type = &vkms_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(vkms_subsys.su_mutex),
+};
+
+int vkms_configfs_register(void)
+{
+	int ret;
+
+	if (is_configfs_registered)
+		return 0;
+
+	config_group_init(&vkms_subsys.su_group);
+	ret = configfs_register_subsystem(&vkms_subsys);
+
+	is_configfs_registered = ret == 0;
+
+	return ret;
+}
+
+void vkms_configfs_unregister(void)
+{
+	if (is_configfs_registered)
+		configfs_unregister_subsystem(&vkms_subsys);
+}
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.h b/drivers/gpu/drm/vkms/vkms_configfs.h
new file mode 100644
index 000000000000..b5d7fab877d5
--- /dev/null
+++ b/drivers/gpu/drm/vkms/vkms_configfs.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef _VKMS_CONFIGFS_H_
+#define _VKMS_CONFIGFS_H_
+
+int vkms_configfs_register(void);
+void vkms_configfs_unregister(void);
+
+#endif /* _VKMS_CONFIGFS_H_ */
diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
index b0a079eb4598..f524a9550017 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.c
+++ b/drivers/gpu/drm/vkms/vkms_drv.c
@@ -27,6 +27,7 @@
 #include <drm/drm_vblank.h>
 
 #include "vkms_config.h"
+#include "vkms_configfs.h"
 #include "vkms_drv.h"
 
 #define DRIVER_NAME	"vkms"
@@ -157,7 +158,7 @@ static int vkms_modeset_init(struct vkms_device *vkmsdev)
 	return vkms_output_init(vkmsdev);
 }
 
-static int vkms_create(struct vkms_config *config)
+int vkms_create(struct vkms_config *config)
 {
 	int ret;
 	struct platform_device *pdev;
@@ -231,12 +232,22 @@ static int __init vkms_init(void)
 
 	ret = vkms_create(config);
 	if (ret)
-		vkms_config_destroy(config);
+		goto err_kfree;
 
+	ret = vkms_configfs_register();
+	if (ret)
+		goto err_destroy;
+
+	return 0;
+
+err_destroy:
+	vkms_destroy(config);
+err_kfree:
+	vkms_config_destroy(config);
 	return ret;
 }
 
-static void vkms_destroy(struct vkms_config *config)
+void vkms_destroy(struct vkms_config *config)
 {
 	struct platform_device *pdev;
 
@@ -257,6 +268,8 @@ static void vkms_destroy(struct vkms_config *config)
 
 static void __exit vkms_exit(void)
 {
+	vkms_configfs_unregister();
+
 	if (default_config->dev)
 		vkms_destroy(default_config);
 
diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index 76394285dc68..eb32440e9f94 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -143,6 +143,10 @@ struct vkms_device {
 #define to_vkms_plane_state(target)\
 	container_of(target, struct vkms_plane_state, base.base)
 
+/* VKMS device */
+int vkms_create(struct vkms_config *config);
+void vkms_destroy(struct vkms_config *config);
+
 /* CRTC */
 struct vkms_crtc *vkms_crtc_init(struct drm_device *dev,
 				 struct drm_plane *primary,
-- 
2.46.0