2 files changed, 156 insertions, 57 deletions

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index ea4e792f789f..78ecb88bad7e 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -223,6 +223,37 @@ void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds)
 }
 EXPORT_SYMBOL_NS_GPL(cxl_dpa_debug, "CXL");
 
+/* See request_skip() kernel-doc */
+static resource_size_t __adjust_skip(struct cxl_dev_state *cxlds,
+				     const resource_size_t skip_base,
+				     const resource_size_t skip_len,
+				     const char *requester)
+{
+	const resource_size_t skip_end = skip_base + skip_len - 1;
+
+	for (int i = 0; i < cxlds->nr_partitions; i++) {
+		const struct resource *part_res = &cxlds->part[i].res;
+		resource_size_t adjust_start, adjust_end, size;
+
+		adjust_start = max(skip_base, part_res->start);
+		adjust_end = min(skip_end, part_res->end);
+
+		if (adjust_end < adjust_start)
+			continue;
+
+		size = adjust_end - adjust_start + 1;
+
+		if (!requester)
+			__release_region(&cxlds->dpa_res, adjust_start, size);
+		else if (!__request_region(&cxlds->dpa_res, adjust_start, size,
+					   requester, 0))
+			return adjust_start - skip_base;
+	}
+
+	return skip_len;
+}
+#define release_skip(c, b, l) __adjust_skip((c), (b), (l), NULL)
+
 /*
  * Must be called in a context that synchronizes against this decoder's
  * port ->remove() callback (like an endpoint decoder sysfs attribute)
@@ -241,7 +272,7 @@ static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
 	skip_start = res->start - cxled->skip;
 	__release_region(&cxlds->dpa_res, res->start, resource_size(res));
 	if (cxled->skip)
-		__release_region(&cxlds->dpa_res, skip_start, cxled->skip);
+		release_skip(cxlds, skip_start, cxled->skip);
 	cxled->skip = 0;
 	cxled->dpa_res = NULL;
 	put_device(&cxled->cxld.dev);
@@ -268,6 +299,58 @@ static void devm_cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
 	__cxl_dpa_release(cxled);
 }
 
+/**
+ * request_skip() - Track DPA 'skip' in @cxlds->dpa_res resource tree
+ * @cxlds: CXL.mem device context that parents @cxled
+ * @cxled: Endpoint decoder establishing new allocation that skips lower DPA
+ * @skip_base: DPA < start of new DPA allocation (DPAnew)
+ * @skip_len: @skip_base + @skip_len == DPAnew
+ *
+ * DPA 'skip' arises from out-of-sequence DPA allocation events relative
+ * to free capacity across multiple partitions. It is a wasteful event
+ * as usable DPA gets thrown away, but if a deployment has, for example,
+ * a dual RAM+PMEM device, wants to use PMEM, and has unallocated RAM
+ * DPA, the free RAM DPA must be sacrificed to start allocating PMEM.
+ * See third "Implementation Note" in CXL 3.1 8.2.4.19.13 "Decoder
+ * Protection" for more details.
+ *
+ * A 'skip' always covers the last allocated DPA in a previous partition
+ * to the start of the current partition to allocate.  Allocations never
+ * start in the middle of a partition, and allocations are always
+ * de-allocated in reverse order (see cxl_dpa_free(), or natural devm
+ * unwind order from forced in-order allocation).
+ *
+ * If @cxlds->nr_partitions was guaranteed to be <= 2 then the 'skip'
+ * would always be contained to a single partition. Given
+ * @cxlds->nr_partitions may be > 2 it results in cases where the 'skip'
+ * might span "tail capacity of partition[0], all of partition[1], ...,
+ * all of partition[N-1]" to support allocating from partition[N]. That
+ * in turn interacts with the partition 'struct resource' boundaries
+ * within @cxlds->dpa_res whereby 'skip' requests need to be divided by
+ * partition. I.e. this is a quirk of using a 'struct resource' tree to
+ * detect range conflicts while also tracking partition boundaries in
+ * @cxlds->dpa_res.
+ */
+static int request_skip(struct cxl_dev_state *cxlds,
+			struct cxl_endpoint_decoder *cxled,
+			const resource_size_t skip_base,
+			const resource_size_t skip_len)
+{
+	resource_size_t skipped = __adjust_skip(cxlds, skip_base, skip_len,
+						dev_name(&cxled->cxld.dev));
+
+	if (skipped == skip_len)
+		return 0;
+
+	dev_dbg(cxlds->dev,
+		"%s: failed to reserve skipped space (%pa %pa %pa)\n",
+		dev_name(&cxled->cxld.dev), &skip_base, &skip_len, &skipped);
+
+	release_skip(cxlds, skip_base, skipped);
+
+	return -EBUSY;
+}
+
 static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 			     resource_size_t base, resource_size_t len,
 			     resource_size_t skipped)
@@ -276,7 +359,9 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	struct cxl_port *port = cxled_to_port(cxled);
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct device *dev = &port->dev;
+	enum cxl_decoder_mode mode;
 	struct resource *res;
+	int rc;
 
 	lockdep_assert_held_write(&cxl_dpa_rwsem);
 
@@ -305,14 +390,9 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	}
 
 	if (skipped) {
-		res = __request_region(&cxlds->dpa_res, base - skipped, skipped,
-				       dev_name(&cxled->cxld.dev), 0);
-		if (!res) {
-			dev_dbg(dev,
-				"decoder%d.%d: failed to reserve skipped space\n",
-				port->id, cxled->cxld.id);
-			return -EBUSY;
-		}
+		rc = request_skip(cxlds, cxled, base - skipped, skipped);
+		if (rc)
+			return rc;
 	}
 	res = __request_region(&cxlds->dpa_res, base, len,
 			       dev_name(&cxled->cxld.dev), 0);
@@ -320,22 +400,23 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 		dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
 			port->id, cxled->cxld.id);
 		if (skipped)
-			__release_region(&cxlds->dpa_res, base - skipped,
-					 skipped);
+			release_skip(cxlds, base - skipped, skipped);
 		return -EBUSY;
 	}
 	cxled->dpa_res = res;
 	cxled->skip = skipped;
 
-	if (to_pmem_res(cxlds) && resource_contains(to_pmem_res(cxlds), res))
-		cxled->mode = CXL_DECODER_PMEM;
-	else if (to_ram_res(cxlds) && resource_contains(to_ram_res(cxlds), res))
-		cxled->mode = CXL_DECODER_RAM;
-	else {
+	mode = CXL_DECODER_NONE;
+	for (int i = 0; cxlds->nr_partitions; i++)
+		if (resource_contains(&cxlds->part[i].res, res)) {
+			mode = cxl_part_mode(cxlds->part[i].mode);
+			break;
+		}
+
+	if (mode == CXL_DECODER_NONE)
 		dev_warn(dev, "decoder%d.%d: %pr does not map any partition\n",
 			 port->id, cxled->cxld.id, res);
-		cxled->mode = CXL_DECODER_NONE;
-	}
+	cxled->mode = mode;
 
 	port->hdm_end++;
 	get_device(&cxled->cxld.dev);
@@ -542,15 +623,13 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
 int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 {
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
-	resource_size_t free_ram_start, free_pmem_start;
 	struct cxl_port *port = cxled_to_port(cxled);
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct device *dev = &cxled->cxld.dev;
-	resource_size_t start, avail, skip;
+	struct resource *res, *prev = NULL;
+	resource_size_t start, avail, skip, skip_start;
 	struct resource *p, *last;
-	const struct resource *ram_res = to_ram_res(cxlds);
-	const struct resource *pmem_res = to_pmem_res(cxlds);
-	int rc;
+	int part, rc;
 
 	down_write(&cxl_dpa_rwsem);
 	if (cxled->cxld.region) {
@@ -566,47 +645,53 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 		goto out;
 	}
 
-	for (p = ram_res->child, last = NULL; p; p = p->sibling)
-		last = p;
-	if (last)
-		free_ram_start = last->end + 1;
-	else
-		free_ram_start = ram_res->start;
+	part = -1;
+	for (int i = 0; i < cxlds->nr_partitions; i++) {
+		if (cxled->mode == cxl_part_mode(cxlds->part[i].mode)) {
+			part = i;
+			break;
+		}
+	}
+
+	if (part < 0) {
+		rc = -EBUSY;
+		goto out;
+	}
 
-	for (p = pmem_res->child, last = NULL; p; p = p->sibling)
+	res = &cxlds->part[part].res;
+	for (p = res->child, last = NULL; p; p = p->sibling)
 		last = p;
 	if (last)
-		free_pmem_start = last->end + 1;
+		start = last->end + 1;
 	else
-		free_pmem_start = pmem_res->start;
+		start = res->start;
 
-	if (cxled->mode == CXL_DECODER_RAM) {
-		start = free_ram_start;
-		avail = ram_res->end - start + 1;
-		skip = 0;
-	} else if (cxled->mode == CXL_DECODER_PMEM) {
-		resource_size_t skip_start, skip_end;
-
-		start = free_pmem_start;
-		avail = pmem_res->end - start + 1;
-		skip_start = free_ram_start;
-
-		/*
-		 * If some pmem is already allocated, then that allocation
-		 * already handled the skip.
-		 */
-		if (pmem_res->child &&
-		    skip_start == pmem_res->child->start)
-			skip_end = skip_start - 1;
-		else
-			skip_end = start - 1;
-		skip = skip_end - skip_start + 1;
-	} else {
-		dev_dbg(dev, "mode not set\n");
-		rc = -EINVAL;
-		goto out;
+	/*
+	 * To allocate at partition N, a skip needs to be calculated for all
+	 * unallocated space at lower partitions indices.
+	 *
+	 * If a partition has any allocations, the search can end because a
+	 * previous cxl_dpa_alloc() invocation is assumed to have accounted for
+	 * all previous partitions.
+	 */
+	skip_start = CXL_RESOURCE_NONE;
+	for (int i = part; i; i--) {
+		prev = &cxlds->part[i - 1].res;
+		for (p = prev->child, last = NULL; p; p = p->sibling)
+			last = p;
+		if (last) {
+			skip_start = last->end + 1;
+			break;
+		}
+		skip_start = prev->start;
 	}
 
+	avail = res->end - start + 1;
+	if (skip_start == CXL_RESOURCE_NONE)
+		skip = 0;
+	else
+		skip = res->start - skip_start;
+
 	if (size > avail) {
 		dev_dbg(dev, "%pa exceeds available %s capacity: %pa\n", &size,
 			cxl_decoder_mode_name(cxled->mode), &avail);
diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
index e33b2d5efed9..9fe615d96573 100644
--- a/drivers/cxl/cxlmem.h
+++ b/drivers/cxl/cxlmem.h
@@ -529,6 +529,20 @@ static inline resource_size_t cxl_pmem_size(struct cxl_dev_state *cxlds)
 	return resource_size(res);
 }
 
+/*
+ * Translate the operational mode of memory capacity with the
+ * operational mode of a decoder
+ * TODO: kill 'enum cxl_decoder_mode' to obviate this helper
+ */
+static inline enum cxl_decoder_mode cxl_part_mode(enum cxl_partition_mode mode)
+{
+	if (mode == CXL_PARTMODE_RAM)
+		return CXL_DECODER_RAM;
+	if (mode == CXL_PARTMODE_PMEM)
+		return CXL_DECODER_PMEM;
+	return CXL_DECODER_NONE;
+}
+
 static inline struct cxl_dev_state *mbox_to_cxlds(struct cxl_mailbox *cxl_mbox)
 {
 	return dev_get_drvdata(cxl_mbox->host);