diff options
Diffstat (limited to 'drivers/gpu/drm/drm_lease.c')
| -rw-r--r-- | drivers/gpu/drm/drm_lease.c | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index 92eac73d9001..79be797e8689 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -15,6 +15,57 @@ #include "drm_crtc_internal.h" #include "drm_internal.h" +/** + * DOC: drm leasing + * + * DRM leases provide information about whether a DRM master may control a DRM + * mode setting object. This enables the creation of multiple DRM masters that + * manage subsets of display resources. + * + * The original DRM master of a device 'owns' the available drm resources. It + * may create additional DRM masters and 'lease' resources which it controls + * to the new DRM master. This gives the new DRM master control over the + * leased resources until the owner revokes the lease, or the new DRM master + * is closed. Some helpful terminology: + * + * - An 'owner' is a &struct drm_master that is not leasing objects from + * another &struct drm_master, and hence 'owns' the objects. The owner can be + * identified as the &struct drm_master for which &drm_master.lessor is NULL. + * + * - A 'lessor' is a &struct drm_master which is leasing objects to one or more + * other &struct drm_master. Currently, lessees are not allowed to + * create sub-leases, hence the lessor is the same as the owner. + * + * - A 'lessee' is a &struct drm_master which is leasing objects from some + * other &struct drm_master. Each lessee only leases resources from a single + * lessor recorded in &drm_master.lessor, and holds the set of objects that + * it is leasing in &drm_master.leases. + * + * - A 'lease' is a contract between the lessor and lessee that identifies + * which resources may be controlled by the lessee. All of the resources + * that are leased must be owned by or leased to the lessor, and lessors are + * not permitted to lease the same object to multiple lessees. + * + * The set of objects any &struct drm_master 'controls' is limited to the set + * of objects it leases (for lessees) or all objects (for owners). + * + * Objects not controlled by a &struct drm_master cannot be modified through + * the various state manipulating ioctls, and any state reported back to user + * space will be edited to make them appear idle and/or unusable. For + * instance, connectors always report 'disconnected', while encoders + * report no possible crtcs or clones. + * + * Since each lessee may lease objects from a single lessor, display resource + * leases form a tree of &struct drm_master. As lessees are currently not + * allowed to create sub-leases, the tree depth is limited to 1. All of + * these get activated simultaneously when the top level device owner changes + * through the SETMASTER or DROPMASTER IOCTL, so &drm_device.master points to + * the owner at the top of the lease tree (i.e. the &struct drm_master for which + * &drm_master.lessor is NULL). The full list of lessees that are leasing + * objects from the owner can be searched via the owner's + * &drm_master.lessee_idr. + */ + #define drm_for_each_lessee(lessee, lessor) \ list_for_each_entry((lessee), &(lessor)->lessees, lessee_list) |