cxl/hdm: Add 'mode' attribute to decoder objects

Recall that the Device Physical Address (DPA) space of a CXL Memory
Expander is potentially partitioned into a volatile and persistent
portion. A decoder maps a Host Physical Address (HPA) range to a DPA
range and that translation depends on the value of all previous (lower
instance number) decoders before the current one.

In preparation for allowing dynamic provisioning of regions, decoders
need an ABI to indicate which DPA partition a decoder targets. This ABI
needs to be prepared for the possibility that some other agent committed
and locked a decoder that spans the partition boundary.

Add 'decoderX.Y/mode' to endpoint decoders that indicates which
partition 'ram' / 'pmem' the decoder targets, or 'mixed' if the decoder
currently spans the partition boundary.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165603881967.551046.6007594190951596439.stgit@dwillia2-xfhSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/ABI/testing/sysfs-bus-cxl

@@ -190,3 +190,19 @@ Description:
 		found to support CDAT data.  If it is present and the length of
 		the data is 0 reading the CDAT data failed.  Otherwise the CDAT
 		data is reported.
+
+
+What:		/sys/bus/cxl/devices/decoderX.Y/mode
+Date:		May, 2022
+KernelVersion:	v5.20
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) When a CXL decoder is of devtype "cxl_decoder_endpoint" it
+		translates from a host physical address range, to a device local
+		address range. Device-local address ranges are further split
+		into a 'ram' (volatile memory) range and 'pmem' (persistent
+		memory) range. The 'mode' attribute emits one of 'ram', 'pmem',
+		'mixed', or 'none'. The 'mixed' indication is for error cases
+		when a decoder straddles the volatile/persistent partition
+		boundary, and 'none' indicates the decoder is not actively
+		decoding, or no DPA allocation policy has been set.

drivers/cxl/core/hdm.c

@@ -226,6 +226,16 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	cxled->dpa_res = res;
 	cxled->skip = skipped;
 
+	if (resource_contains(&cxlds->pmem_res, res))
+		cxled->mode = CXL_DECODER_PMEM;
+	else if (resource_contains(&cxlds->ram_res, res))
+		cxled->mode = CXL_DECODER_RAM;
+	else {
+		dev_dbg(dev, "decoder%d.%d: %pr mixed\n", port->id,
+			cxled->cxld.id, cxled->dpa_res);
+		cxled->mode = CXL_DECODER_MIXED;
+	}
+
 	return 0;
 }
 

drivers/cxl/core/port.c

@@ -172,6 +172,25 @@ static ssize_t target_list_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(target_list);
 
+static ssize_t mode_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct cxl_endpoint_decoder *cxled = to_cxl_endpoint_decoder(dev);
+
+	switch (cxled->mode) {
+	case CXL_DECODER_RAM:
+		return sysfs_emit(buf, "ram\n");
+	case CXL_DECODER_PMEM:
+		return sysfs_emit(buf, "pmem\n");
+	case CXL_DECODER_NONE:
+		return sysfs_emit(buf, "none\n");
+	case CXL_DECODER_MIXED:
+	default:
+		return sysfs_emit(buf, "mixed\n");
+	}
+}
+static DEVICE_ATTR_RO(mode);
+
 static struct attribute *cxl_decoder_base_attrs[] = {
 	&dev_attr_start.attr,
 	&dev_attr_size.attr,
@@ -222,6 +241,7 @@ static const struct attribute_group *cxl_decoder_switch_attribute_groups[] = {
 
 static struct attribute *cxl_decoder_endpoint_attrs[] = {
 	&dev_attr_target_type.attr,
+	&dev_attr_mode.attr,
 	NULL,
 };
 

drivers/cxl/cxl.h

@@ -241,16 +241,25 @@ struct cxl_decoder {
 	unsigned long flags;
 };
 
+enum cxl_decoder_mode {
+	CXL_DECODER_NONE,
+	CXL_DECODER_RAM,
+	CXL_DECODER_PMEM,
+	CXL_DECODER_MIXED,
+};
+
 /**
  * struct cxl_endpoint_decoder - Endpoint  / SPA to DPA decoder
  * @cxld: base cxl_decoder_object
  * @dpa_res: actively claimed DPA span of this decoder
  * @skip: offset into @dpa_res where @cxld.hpa_range maps
+ * @mode: which memory type / access-mode-partition this decoder targets
  */
 struct cxl_endpoint_decoder {
 	struct cxl_decoder cxld;
 	struct resource *dpa_res;
 	resource_size_t skip;
+	enum cxl_decoder_mode mode;
 };
 
 /**