On Tue, 05 Nov 2024 12:38:42 -0600 ira.weiny@xxxxxxxxx wrote: > From: Navneet Singh <navneet.singh@xxxxxxxxx> > > A dynamic capacity device (DCD) sends events to signal the host for > changes in the availability of Dynamic Capacity (DC) memory. These > events contain extents describing a DPA range and meta data for memory > to be added or removed. Events may be sent from the device at any time. > > Three types of events can be signaled, Add, Release, and Force Release. > > On add, the host may accept or reject the memory being offered. If no > region exists, or the extent is invalid, the extent should be rejected. > Add extent events may be grouped by a 'more' bit which indicates those > extents should be processed as a group. > > On remove, the host can delay the response until the host is safely not > using the memory. If no region exists the release can be sent > immediately. The host may also release extents (or partial extents) at > any time. Thus the 'more' bit grouping of release events is of less > value and can be ignored in favor of sending multiple release capacity > responses for groups of release events. > > Force removal is intended as a mechanism between the FM and the device > and intended only when the host is unresponsive, out of sync, or > otherwise broken. Purposely ignore force removal events. > > Regions are made up of one or more devices which may be surfacing memory > to the host. Once all devices in a region have surfaced an extent the > region can expose a corresponding extent for the user to consume. > Without interleaving a device extent forms a 1:1 relationship with the > region extent. Immediately surface a region extent upon getting a > device extent. > > Per the specification the device is allowed to offer or remove extents > at any time. However, anticipated use cases can expect extents to be > offered, accepted, and removed in well defined chunks. > > Simplify extent tracking with the following restrictions. > > 1) Flag for removal any extent which overlaps a requested > release range. > 2) Refuse the offer of extents which overlap already accepted > memory ranges. > 3) Accept again a range which has already been accepted by the > host. Eating duplicates serves three purposes. First, this > simplifies the code if the device should get out of sync with > the host. And it should be safe to acknowledge the extent > again. Second, this simplifies the code to process existing > extents if the extent list should change while the extent > list is being read. Third, duplicates for a given region > which are seen during a race between the hardware surfacing > an extent and the cxl dax driver scanning for existing > extents will be ignored. > > NOTE: Processing existing extents is done in a later patch. > > Management of the region extent devices must be synchronized with > potential uses of the memory within the DAX layer. Create region extent > devices as children of the cxl_dax_region device such that the DAX > region driver can co-drive them and synchronize with the DAX layer. > Synchronization and management is handled in a subsequent patch. > > Tag support within the DAX layer is not yet supported. To maintain > compatibility legacy DAX/region processing only tags with a value of 0 > are allowed. This defines existing DAX devices as having a 0 tag which > makes the most logical sense as a default. > > Process DCD events and create region devices. > > Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx> > Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx> > Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> > I gave this on v5, but meh here it is again (obviously subject to Li Ming's fix which maybe can just get rolled in whilst applying) Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
