drm/vkms: Allow to configure CRTC writeback support via configfs

When a CRTC is created, add a `writeback` file to allow to enable or
disable writeback connector support

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/20251016175618.10051-7-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 7396447b5e5839fd9cbc6b71508156c9a43141f5..9f76918bb1d17153194addfbfb68748dbe4b6677 100644 (file)
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -94,6 +94,10 @@ Continue by creating one or more CRTCs::
 
   sudo mkdir /config/vkms/my-vkms/crtcs/crtc0
 
+CRTCs have 1 configurable attribute:
+
+- writeback: Enable or disable writeback connector support by writing 1 or 0
+
 Once you are done configuring the VKMS instance, enable it::
 
   echo "1" | sudo tee /config/vkms/my-vkms/enabled

diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 62a82366791d107643bb1727939a94cec50cf257..e9f445043268d207771ff5a773b6d59731103234 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -74,6 +74,47 @@ struct vkms_configfs_crtc {
 #define crtc_item_to_vkms_configfs_crtc(item) \
        container_of(to_config_group((item)), struct vkms_configfs_crtc, group)
 
+static ssize_t crtc_writeback_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_crtc *crtc;
+       bool writeback;
+
+       crtc = crtc_item_to_vkms_configfs_crtc(item);
+
+       scoped_guard(mutex, &crtc->dev->lock)
+               writeback = vkms_config_crtc_get_writeback(crtc->config);
+
+       return sprintf(page, "%d\n", writeback);
+}
+
+static ssize_t crtc_writeback_store(struct config_item *item, const char *page,
+                                   size_t count)
+{
+       struct vkms_configfs_crtc *crtc;
+       bool writeback;
+
+       crtc = crtc_item_to_vkms_configfs_crtc(item);
+
+       if (kstrtobool(page, &writeback))
+               return -EINVAL;
+
+       scoped_guard(mutex, &crtc->dev->lock) {
+               if (crtc->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_crtc_set_writeback(crtc->config, writeback);
+       }
+
+       return (ssize_t)count;
+}
+
+CONFIGFS_ATTR(crtc_, writeback);
+
+static struct configfs_attribute *crtc_item_attrs[] = {
+       &crtc_attr_writeback,
+       NULL,
+};
+
 static void crtc_release(struct config_item *item)
 {
        struct vkms_configfs_crtc *crtc;
@@ -93,6 +134,7 @@ static struct configfs_item_operations crtc_item_operations = {
 };
 
 static const struct config_item_type crtc_item_type = {
+       .ct_attrs       = crtc_item_attrs,
        .ct_item_ops    = &crtc_item_operations,
        .ct_owner       = THIS_MODULE,
 };