cxl/hdm: Add sysfs attributes for interleave ways + granularity

The region provisioning flow involves selecting interleave ways +
granularity settings for a region, and then programming the decoder
topology to meet those constraints, if possible. For example, root
decoders set the minimum interleave ways + granularity for any hosted
regions.

Given decoder programming is not atomic and collisions can occur between
multiple requesting regions userspace will be responsible for conflict
resolution and it needs these attributes to make those decisions.

Signed-off-by: Ben Widawsky <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Link: https://lore.kernel.org/r/165784332235.1758207.7185062713652694607.stgit@dwillia2-xfh.jf.intel.com
[djbw: reword changelog, make read-only, add sysfs ABI documentaion]
Signed-off-by: Dan Williams <[email protected]>

Author: Ben Widawsky

Documentation/ABI/testing/sysfs-bus-cxl

@@ -241,3 +241,30 @@ Description:
 		allocations are enforced to occur in increasing 'decoderX.Y/id'
 		order and frees are enforced to occur in decreasing
 		'decoderX.Y/id' order.
+
+
+What:		/sys/bus/cxl/devices/decoderX.Y/interleave_ways
+Date:		May, 2022
+KernelVersion:	v5.20
+Contact:	[email protected]
+Description:
+		(RO) The number of targets across which this decoder's host
+		physical address (HPA) memory range is interleaved. The device
+		maps every Nth block of HPA (of size ==
+		'interleave_granularity') to consecutive DPA addresses. The
+		decoder's position in the interleave is determined by the
+		device's (endpoint or switch) switch ancestry. For root
+		decoders their interleave is specified by platform firmware and
+		they only specify a downstream target order for host bridges.
+
+
+What:		/sys/bus/cxl/devices/decoderX.Y/interleave_granularity
+Date:		May, 2022
+KernelVersion:	v5.20
+Contact:	[email protected]
+Description:
+		(RO) The number of consecutive bytes of host physical address
+		space this decoder claims at address N before the decode rotates
+		to the next target in the interleave at address N +
+		interleave_granularity (assuming N is aligned to
+		interleave_granularity).

drivers/cxl/core/port.c

@@ -260,10 +260,33 @@ static ssize_t dpa_size_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(dpa_size);
 
+static ssize_t interleave_granularity_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	struct cxl_decoder *cxld = to_cxl_decoder(dev);
+
+	return sysfs_emit(buf, "%d\n", cxld->interleave_granularity);
+}
+
+static DEVICE_ATTR_RO(interleave_granularity);
+
+static ssize_t interleave_ways_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct cxl_decoder *cxld = to_cxl_decoder(dev);
+
+	return sysfs_emit(buf, "%d\n", cxld->interleave_ways);
+}
+
+static DEVICE_ATTR_RO(interleave_ways);
+
 static struct attribute *cxl_decoder_base_attrs[] = {
 	&dev_attr_start.attr,
 	&dev_attr_size.attr,
 	&dev_attr_locked.attr,
+	&dev_attr_interleave_granularity.attr,
+	&dev_attr_interleave_ways.attr,
 	NULL,
 };