[PATCH v6 1/5] drm: add card symlink in render sysfs directory

[Lionel Landwerlin]

In i915 we would like to expose information about the GPU topology
which would be useful mostly to applications making use of the device
computational capability (not so much the display part). At the moment
we already store information like frequency, etc... into the card
directory (/sys/class/drm/card0). It seems natural to add the
additional data there too.

Unfortunately it's not obvious how to go from the render node back to
the sysfs card directory.

>From the major/minor number it's possible to figure out what device
associated with the render node. For example with this render node :

$ ls -l /dev/dri/renderD128
crw-rw----+ 1 root video 226, 128 Oct 24 16:17 /dev/dri/renderD128

You can rebuild a part to access the associated drm device in :

$ ls -l /sys/dev/char/226\:128/device/drm/
total 0
drwxr-xr-x 9 root root 0 Nov 27 16:52 card0
lrwxrwxrwx 1 root root 0 Nov 27 16:52 controlD64 -> card0
drwxr-xr-x 3 root root 0 Nov 27 16:50 renderD128

Right now, most devices have usually only one card. But in order to be
future proof, we would like to associate the render node with the card
so that you can get access to the card with the following path :

/sys/dev/char/226\:128/card/

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Cc: dri-devel at lists.freedesktop.org
---
 drivers/gpu/drm/drm_drv.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 9acc1e157813..a26c0e86778e 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -779,6 +779,14 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_modeset_register_all(dev);
 
+	if (drm_core_check_feature(dev, DRIVER_RENDER)) {
+		ret = sysfs_create_link(&dev->render->kdev->kobj,
+					&dev->primary->kdev->kobj,
+					"card");
+		if (ret)
+			goto err_minors;
+	}
+
 	ret = 0;
 
 	DRM_INFO("Initialized %s %d.%d.%d %s for %s on minor %d\n",
@@ -835,6 +843,9 @@ void drm_dev_unregister(struct drm_device *dev)
 	list_for_each_entry_safe(r_list, list_temp, &dev->maplist, head)
 		drm_legacy_rmmap(dev, r_list->map);
 
+	if (drm_core_check_feature(dev, DRIVER_RENDER))
+		sysfs_remove_link(&dev->render->kdev->kobj, "card");
+
 	remove_compat_control_link(dev);
 	drm_minor_unregister(dev, DRM_MINOR_PRIMARY);
 	drm_minor_unregister(dev, DRM_MINOR_RENDER);
-- 
2.15.1