[PATCH ndctl 5/7] cxl/region: determine region type based on root decoder capability

[Vishal Verma <vishal.l.verma@intel.com>]

In the common case, root decoders are expected to be either pmem
capable, or volatile capable, but not necessarily both simultaneously.
If a decoder only has one of pmem or volatile capabilities,
cxl-create-region should just infer the type of the region (pmem
or ram) based on this capability.

Maintain the default behavior of cxl-create-region to choose type=pmem,
but only as a fallback if the selected root decoder has multiple
capabilities. If it is only capable of either pmem, or ram, then infer
region type from this without requiring it to be specified explicitly.

Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 Documentation/cxl/cxl-create-region.txt |  3 ++-
 cxl/region.c                            | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/Documentation/cxl/cxl-create-region.txt b/Documentation/cxl/cxl-create-region.txt
index ada0e52..f11a412 100644
--- a/Documentation/cxl/cxl-create-region.txt
+++ b/Documentation/cxl/cxl-create-region.txt
@@ -75,7 +75,8 @@ include::bus-option.txt[]
 
 -t::
 --type=::
-	Specify the region type - 'pmem' or 'ram'. Defaults to 'pmem'.
+	Specify the region type - 'pmem' or 'ram'. Default to root decoder
+	capability, and if that is ambiguous, default to 'pmem'.
 
 -U::
 --uuid=::
diff --git a/cxl/region.c b/cxl/region.c
index 9079b2d..1c8ccc7 100644
--- a/cxl/region.c
+++ b/cxl/region.c
@@ -448,6 +448,31 @@ static int validate_decoder(struct cxl_decoder *decoder,
 	return 0;
 }
 
+static void set_type_from_decoder(struct cxl_ctx *ctx, struct parsed_params *p)
+{
+	int num_cap = 0;
+
+	/* if param.type was explicitly specified, nothing to do here */
+	if (param.type)
+		return;
+
+	/*
+	 * if the root decoder only has one type of capability, default
+	 * to that mode for the region.
+	 */
+	if (cxl_decoder_is_pmem_capable(p->root_decoder))
+		num_cap++;
+	if (cxl_decoder_is_volatile_capable(p->root_decoder))
+		num_cap++;
+
+	if (num_cap == 1) {
+		if (cxl_decoder_is_volatile_capable(p->root_decoder))
+			p->mode = CXL_DECODER_MODE_RAM;
+		else if (cxl_decoder_is_pmem_capable(p->root_decoder))
+			p->mode = CXL_DECODER_MODE_PMEM;
+	}
+}
+
 static int create_region_validate_config(struct cxl_ctx *ctx,
 					 struct parsed_params *p)
 {
@@ -481,6 +506,8 @@ found:
 		return -ENXIO;
 	}
 
+	set_type_from_decoder(ctx, p);
+
 	rc = validate_decoder(p->root_decoder, p);
 	if (rc)
 		return rc;

-- 
2.39.1