drm/vkms: Allow to attach encoders and CRTCs via configfs

Create a default subgroup at
/config/vkms/encoders/encoder/possible_crtcs that will contain symbolic
links to the possible CRTCs for the encoder.

Tested-by: Mark Yacoub <markyacoub@google.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@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>
Link: https://lore.kernel.org/r/20251016175618.10051-10-jose.exposito89@gmail.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 622fbfa12a84c0d0bf9d40a262c73d0464893a4c..585effe9055093d36f7ade983697e0125534ea76 100644 (file)
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -106,6 +106,7 @@ Next, create one or more encoders::
 To finish the configuration, link the different pipeline items::
 
   sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/planes/plane0/possible_crtcs
+  sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/encoders/encoder0/possible_crtcs
 
 Since at least one primary plane is required, make sure to set the right type::
 
@@ -122,6 +123,7 @@ Finally, you can remove the VKMS instance disabling it::
 And removing the top level directory and its subdirectories::
 
   sudo rm /config/vkms/my-vkms/planes/*/possible_crtcs/*
+  sudo rm /config/vkms/my-vkms/encoders/*/possible_crtcs/*
   sudo rmdir /config/vkms/my-vkms/planes/*
   sudo rmdir /config/vkms/my-vkms/crtcs/*
   sudo rmdir /config/vkms/my-vkms/encoders/*

diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 0df86e63570a1be2caee12588cacf3b93171d05f..7de601e39d2bc04bc35e33ab23340d3d767d77c3 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -70,11 +70,13 @@ struct vkms_configfs_crtc {
  *
  * @group: Top level configuration group that represents a encoder.
  * Initialized when a new directory is created under "/config/vkms/encoders"
+ * @possible_crtcs_group: Default subgroup of @group at "encoder/possible_crtcs"
  * @dev: The vkms_configfs_device this encoder belongs to
  * @config: Configuration of the VKMS encoder
  */
 struct vkms_configfs_encoder {
        struct config_group group;
+       struct config_group possible_crtcs_group;
        struct vkms_configfs_device *dev;
        struct vkms_config_encoder *config;
 };
@@ -100,6 +102,10 @@ struct vkms_configfs_encoder {
        container_of(to_config_group((item)), struct vkms_configfs_encoder, \
                     group)
 
+#define encoder_possible_crtcs_item_to_vkms_configfs_encoder(item) \
+       container_of(to_config_group((item)), struct vkms_configfs_encoder, \
+                    possible_crtcs_group)
+
 static ssize_t crtc_writeback_show(struct config_item *item, char *page)
 {
        struct vkms_configfs_crtc *crtc;
@@ -364,6 +370,52 @@ static const struct config_item_type plane_group_type = {
        .ct_owner       = THIS_MODULE,
 };
 
+static int encoder_possible_crtcs_allow_link(struct config_item *src,
+                                            struct config_item *target)
+{
+       struct vkms_configfs_encoder *encoder;
+       struct vkms_configfs_crtc *crtc;
+       int ret;
+
+       if (target->ci_type != &crtc_item_type)
+               return -EINVAL;
+
+       encoder = encoder_possible_crtcs_item_to_vkms_configfs_encoder(src);
+       crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+       scoped_guard(mutex, &encoder->dev->lock) {
+               if (encoder->dev->enabled)
+                       return -EBUSY;
+
+               ret = vkms_config_encoder_attach_crtc(encoder->config, crtc->config);
+       }
+
+       return ret;
+}
+
+static void encoder_possible_crtcs_drop_link(struct config_item *src,
+                                            struct config_item *target)
+{
+       struct vkms_configfs_encoder *encoder;
+       struct vkms_configfs_crtc *crtc;
+
+       encoder = encoder_possible_crtcs_item_to_vkms_configfs_encoder(src);
+       crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+       scoped_guard(mutex, &encoder->dev->lock)
+               vkms_config_encoder_detach_crtc(encoder->config, crtc->config);
+}
+
+static struct configfs_item_operations encoder_possible_crtcs_item_operations = {
+       .allow_link     = encoder_possible_crtcs_allow_link,
+       .drop_link      = encoder_possible_crtcs_drop_link,
+};
+
+static const struct config_item_type encoder_possible_crtcs_group_type = {
+       .ct_item_ops    = &encoder_possible_crtcs_item_operations,
+       .ct_owner       = THIS_MODULE,
+};
+
 static void encoder_release(struct config_item *item)
 {
        struct vkms_configfs_encoder *encoder;
@@ -413,6 +465,12 @@ static struct config_group *make_encoder_group(struct config_group *group,
 
                config_group_init_type_name(&encoder->group, name,
                                            &encoder_item_type);
+
+               config_group_init_type_name(&encoder->possible_crtcs_group,
+                                           "possible_crtcs",
+                                           &encoder_possible_crtcs_group_type);
+               configfs_add_default_group(&encoder->possible_crtcs_group,
+                                          &encoder->group);
        }
 
        return &encoder->group;