[PATCH v3 07/14] drm/vkms: Add a validation function for VKMS configuration

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

From: Louis Chauvet <louis.chauvet@bootlin.com>

As the configuration will be used by userspace, add a validator to avoid
creating a broken DRM device.

For the moment, the function always returns true, but rules will be
added in future patches.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
Co-developed-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 drivers/gpu/drm/vkms/tests/vkms_config_test.c |  2 ++
 drivers/gpu/drm/vkms/vkms_config.c            |  6 ++++++
 drivers/gpu/drm/vkms/vkms_config.h            | 10 ++++++++++
 drivers/gpu/drm/vkms/vkms_output.c            |  3 +++
 4 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/vkms/tests/vkms_config_test.c b/drivers/gpu/drm/vkms/tests/vkms_config_test.c
index 92798590051b..6e07139d261c 100644
--- a/drivers/gpu/drm/vkms/tests/vkms_config_test.c
+++ b/drivers/gpu/drm/vkms/tests/vkms_config_test.c
@@ -54,6 +54,8 @@ static void vkms_config_test_default_config(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, config->writeback, params->enable_writeback);
 	KUNIT_EXPECT_EQ(test, config->overlay, params->enable_overlay);
 
+	KUNIT_EXPECT_TRUE(test, vkms_config_is_valid(config));
+
 	vkms_config_destroy(config);
 }
 
diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
index 9fb08d94a351..d1947537834c 100644
--- a/drivers/gpu/drm/vkms/vkms_config.c
+++ b/drivers/gpu/drm/vkms/vkms_config.c
@@ -51,6 +51,12 @@ void vkms_config_destroy(struct vkms_config *config)
 }
 EXPORT_SYMBOL_IF_KUNIT(vkms_config_destroy);
 
+bool vkms_config_is_valid(const struct vkms_config *config)
+{
+	return true;
+}
+EXPORT_SYMBOL_IF_KUNIT(vkms_config_is_valid);
+
 static int vkms_config_show(struct seq_file *m, void *data)
 {
 	struct drm_debugfs_entry *entry = m->private;
diff --git a/drivers/gpu/drm/vkms/vkms_config.h b/drivers/gpu/drm/vkms/vkms_config.h
index fcaa909fb2e0..31c758631c37 100644
--- a/drivers/gpu/drm/vkms/vkms_config.h
+++ b/drivers/gpu/drm/vkms/vkms_config.h
@@ -67,6 +67,16 @@ vkms_config_get_device_name(struct vkms_config *config)
 	return config->dev_name;
 }
 
+/**
+ * vkms_config_is_valid() - Validate a configuration
+ * @config: Configuration to validate
+ *
+ * Returns:
+ * Whether the configuration is valid or not.
+ * For example, a configuration without primary planes is not valid.
+ */
+bool vkms_config_is_valid(const struct vkms_config *config);
+
 /**
  * vkms_config_register_debugfs() - Register a debugfs file to show the device's
  * configuration
diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
index 068a7f87ecec..414cc933af41 100644
--- a/drivers/gpu/drm/vkms/vkms_output.c
+++ b/drivers/gpu/drm/vkms/vkms_output.c
@@ -16,6 +16,9 @@ int vkms_output_init(struct vkms_device *vkmsdev)
 	int writeback;
 	unsigned int n;
 
+	if (!vkms_config_is_valid(vkmsdev->config))
+		return -EINVAL;
+
 	/*
 	 * Initialize used plane. One primary plane is required to perform the composition.
 	 *
-- 
2.48.1