cxl/region: Add region creation support

CXL 2.0 allows for dynamic provisioning of new memory regions (system
physical address resources like "System RAM" and "Persistent Memory").
Whereas DDR and PMEM resources are conveyed statically at boot, CXL
allows for assembling and instantiating new regions from the available
capacity of CXL memory expanders in the system.

Sysfs with an "echo $region_name > $create_region_attribute" interface
is chosen as the mechanism to initiate the provisioning process. This
was chosen over ioctl() and netlink() to keep the configuration
interface entirely in a pseudo-fs interface, and it was chosen over
configfs since, aside from this one creation event, the interface is
read-mostly. I.e. configfs supports cases where an object is designed to
be provisioned each boot, like an iSCSI storage target, and CXL region
creation is mostly for PMEM regions which are created usually once
per-lifetime of a server instance. This is an improvement over nvdimm
that pre-created "seed" devices that tended to confuse users looking to
determine which devices are active and which are idle.

Recall that the major change that CXL brings over previous persistent
memory architectures is the ability to dynamically define new regions.
Compare that to drivers like 'nfit' where the region configuration is
statically defined by platform firmware.

Regions are created as a child of a root decoder that encompasses an
address space with constraints. When created through sysfs, the root
decoder is explicit. When created from an LSA's region structure a root
decoder will possibly need to be inferred by the driver.

Upon region creation through sysfs, a vacant region is created with a
unique name. Regions have a number of attributes that must be configured
before the region can be bound to the driver where HDM decoder program
is completed.

An example of creating a new region:

- Allocate a new region name:
region=$(cat /sys/bus/cxl/devices/decoder0.0/create_pmem_region)

- Create a new region by name:
while
region=$(cat /sys/bus/cxl/devices/decoder0.0/create_pmem_region)
! echo $region > /sys/bus/cxl/devices/decoder0.0/create_pmem_region
do true; done

- Region now exists in sysfs:
stat -t /sys/bus/cxl/devices/decoder0.0/$region

- Delete the region, and name:
echo $region > /sys/bus/cxl/devices/decoder0.0/delete_region

Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165784333909.1758207.794374602146306032.stgit@dwillia2-xfh.jf.intel.com
[djbw: simplify locking, reword changelog]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index c3c62568d287..0b38ee99bddf 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -286,14 +286,30 @@ struct cxl_switch_decoder {
 /**
  * struct cxl_root_decoder - Static platform CXL address decoder
  * @res: host / parent resource for region allocations
+ * @region_id: region id for next region provisioning event
  * @cxlsd: base cxl switch decoder
  */
 struct cxl_root_decoder {
 	struct resource *res;
+	atomic_t region_id;
 	struct cxl_switch_decoder cxlsd;
 };
 
 /**
+ * struct cxl_region - CXL region
+ * @dev: This region's device
+ * @id: This region's id. Id is globally unique across all regions
+ * @mode: Endpoint decoder allocation / access mode
+ * @type: Endpoint decoder target type
+ */
+struct cxl_region {
+	struct device dev;
+	int id;
+	enum cxl_decoder_mode mode;
+	enum cxl_decoder_type type;
+};
+
+/**
  * enum cxl_nvdimm_brige_state - state machine for managing bus rescans
  * @CXL_NVB_NEW: Set at bridge create and after cxl_pmem_wq is destroyed
  * @CXL_NVB_DEAD: Set at brige unregistration to preclude async probing
@@ -447,6 +463,8 @@ struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port);
 int devm_cxl_enumerate_decoders(struct cxl_hdm *cxlhdm);
 int devm_cxl_add_passthrough_decoder(struct cxl_port *port);
 
+bool is_cxl_region(struct device *dev);
+
 extern struct bus_type cxl_bus_type;
 
 struct cxl_driver {