cxl/region: Add interleave geometry attributes

Add ABI to allow the number of devices that comprise a region to be
set as well as the interleave granularity for the region.

Signed-off-by: Ben Widawsky <[e-mail]>
[djbw: reword changelog]
Reviewed-by: Jonathan Cameron <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

Documentation/ABI/testing/sysfs-bus-cxl

···
 		(RW) Write a unique identifier for the region. This field must
 		be set for persistent regions and it must not conflict with the
 		UUID of another region.
+
+
+What:		/sys/bus/cxl/devices/regionZ/interleave_granularity
+Date:		May, 2022
+KernelVersion:	v5.20
+Contact:	[e-mail]
+Description:
+		(RW) Set the number of consecutive bytes each device in the
+		interleave set will claim. The possible interleave granularity
+		values are determined by the CXL spec and the participating
+		devices.
+
+
+What:		/sys/bus/cxl/devices/regionZ/interleave_ways
+Date:		May, 2022
+KernelVersion:	v5.20
+Contact:	[e-mail]
+Description:
+		(RW) Configures the number of devices participating in the
+		region is set by writing this value. Each device will provide
+		1/interleave_ways of storage for the region.

drivers/cxl/core/region.c

···
 #include <linux/slab.h>
 #include <linux/uuid.h>
 #include <linux/idr.h>
+#include <cxlmem.h>
 #include <cxl.h>
 #include "core.h"
 
···
  *
  * Region configuration has ordering constraints. UUID may be set at any time
  * but is only visible for persistent regions.
+ * 1. Interleave granularity
+ * 2. Interleave size
  */
 
 /*
···
 	return a->mode;
 }
 
+static ssize_t interleave_ways_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_region_params *p = &cxlr->params;
+	ssize_t rc;
+
+	rc = down_read_interruptible(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	rc = sysfs_emit(buf, "%d\n", p->interleave_ways);
+	up_read(&cxl_region_rwsem);
+
+	return rc;
+}
+
+static ssize_t interleave_ways_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t len)
+{
+	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
+	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_region_params *p = &cxlr->params;
+	int rc, val;
+	u8 iw;
+
+	rc = kstrtoint(buf, 0, &val);
+	if (rc)
+		return rc;
+
+	rc = ways_to_cxl(val, &iw);
+	if (rc)
+		return rc;
+
+	/*
+	 * Even for x3, x9, and x12 interleaves the region interleave must be a
+	 * power of 2 multiple of the host bridge interleave.
+	 */
+	if (!is_power_of_2(val / cxld->interleave_ways) ||
+	    (val % cxld->interleave_ways)) {
+		dev_dbg(&cxlr->dev, "invalid interleave: %d\n", val);
+		return -EINVAL;
+	}
+
+	rc = down_write_killable(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
+		rc = -EBUSY;
+		goto out;
+	}
+
+	p->interleave_ways = val;
+out:
+	up_write(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	return len;
+}
+static DEVICE_ATTR_RW(interleave_ways);
+
+static ssize_t interleave_granularity_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_region_params *p = &cxlr->params;
+	ssize_t rc;
+
+	rc = down_read_interruptible(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	rc = sysfs_emit(buf, "%d\n", p->interleave_granularity);
+	up_read(&cxl_region_rwsem);
+
+	return rc;
+}
+
+static ssize_t interleave_granularity_store(struct device *dev,
+					    struct device_attribute *attr,
+					    const char *buf, size_t len)
+{
+	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
+	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_region_params *p = &cxlr->params;
+	int rc, val;
+	u16 ig;
+
+	rc = kstrtoint(buf, 0, &val);
+	if (rc)
+		return rc;
+
+	rc = granularity_to_cxl(val, &ig);
+	if (rc)
+		return rc;
+
+	/*
+	 * Disallow region granularity less than root granularity to
+	 * simplify the implementation. Otherwise, region's with a
+	 * granularity less than the root interleave result in needing
+	 * multiple endpoints to support a single slot in the
+	 * interleave.
+	 */
+	if (val < cxld->interleave_granularity)
+		return -EINVAL;
+
+	rc = down_write_killable(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
+		rc = -EBUSY;
+		goto out;
+	}
+
+	p->interleave_granularity = val;
+out:
+	up_write(&cxl_region_rwsem);
+	if (rc)
+		return rc;
+	return len;
+}
+static DEVICE_ATTR_RW(interleave_granularity);
+
 static struct attribute *cxl_region_attrs[] = {
 	&dev_attr_uuid.attr,
+	&dev_attr_interleave_ways.attr,
+	&dev_attr_interleave_granularity.attr,
 	NULL,
 };
 
···
 					      enum cxl_decoder_type type)
 {
 	struct cxl_port *port = to_cxl_port(cxlrd->cxlsd.cxld.dev.parent);
+	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
+	struct cxl_region_params *p;
 	struct cxl_region *cxlr;
 	struct device *dev;
 	int rc;
···
 	cxlr = cxl_region_alloc(cxlrd, id);
 	if (IS_ERR(cxlr))
 		return cxlr;
+	p = &cxlr->params;
 	cxlr->mode = mode;
 	cxlr->type = type;
+	p->interleave_granularity = cxld->interleave_granularity;
 
 	dev = &cxlr->dev;
 	rc = dev_set_name(dev, "region%d", id);

drivers/cxl/cxl.h

···
 #include <linux/libnvdimm.h>
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
+#include <linux/log2.h>
 #include <linux/io.h>
 
 /**
···
 		return -EINVAL;
 	}
 
+	return 0;
+}
+
+static inline int granularity_to_cxl(int g, u16 *ig)
+{
+	if (g > SZ_16K || g < 256 || !is_power_of_2(g))
+		return -EINVAL;
+	*ig = ilog2(g) - 8;
+	return 0;
+}
+
+static inline int ways_to_cxl(int ways, u8 *iw)
+{
+	if (ways > 16)
+		return -EINVAL;
+	if (is_power_of_2(ways)) {
+		*iw = ilog2(ways);
+		return 0;
+	}
+	if (ways % 3)
+		return -EINVAL;
+	ways /= 3;
+	if (!is_power_of_2(ways))
+		return -EINVAL;
+	*iw = ilog2(ways) + 8;
 	return 0;
 }
 
···
 /*
  * enum cxl_config_state - State machine for region configuration
  * @CXL_CONFIG_IDLE: Any sysfs attribute can be written freely
+ * @CXL_CONFIG_INTERLEAVE_ACTIVE: region size has been set, no more
+ * changes to interleave_ways or interleave_granularity
  * @CXL_CONFIG_ACTIVE: All targets have been added the region is now
  * active
  */
 enum cxl_config_state {
 	CXL_CONFIG_IDLE,
+	CXL_CONFIG_INTERLEAVE_ACTIVE,
 	CXL_CONFIG_ACTIVE,
 };
 
···
  * struct cxl_region_params - region settings
  * @state: allow the driver to lockdown further parameter changes
  * @uuid: unique id for persistent regions
+ * @interleave_ways: number of endpoints in the region
+ * @interleave_granularity: capacity each endpoint contributes to a stripe
  *
  * State transitions are protected by the cxl_region_rwsem
  */
 struct cxl_region_params {
 	enum cxl_config_state state;
 	uuid_t uuid;
+	int interleave_ways;
+	int interleave_granularity;
 };
 
 /**