cxl/region: Fix 'distance' calculation with passthrough ports

When programming port decode targets, the algorithm wants to ensure that
two devices are compatible to be programmed as peers beneath a given
port. A compatible peer is a target that shares the same dport, and
where that target's interleave position also routes it to the same
dport. Compatibility is determined by the device's interleave position
being >= to distance. For example, if a given dport can only map every
Nth position then positions less than N away from the last target
programmed are incompatible.

The @distance for the host-bridge's cxl_port in a simple dual-ported
host-bridge configuration with 2 direct-attached devices is 1, i.e. An
x2 region divided by 2 dports to reach 2 region targets.

An x4 region under an x2 host-bridge would need 2 intervening switches
where the @distance at the host bridge level is 2 (x4 region divided by
2 switches to reach 4 devices).

However, the distance between peers underneath a single ported
host-bridge is always zero because there is no limit to the number of
devices that can be mapped. In other words, there are no decoders to
program in a passthrough, all descendants are mapped and distance only
starts matters for the intervening descendant ports of the passthrough
port.

Add tracking for the number of dports mapped to a port, and use that to
detect the passthrough case for calculating @distance.

Cc: <stable@vger.kernel.org>
Reported-by: Bobo WL <lmw.bobo@gmail.com>
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: http://lore.kernel.org/r/20221010172057.00001559@huawei.com
Fixes: 27b3f8d13830 ("cxl/region: Program target lists")
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/166752185440.947915.6617495912508299445.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index bffde86..e755686 100644 (file)
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -811,6 +811,7 @@ static struct cxl_dport *find_dport(struct cxl_port *port, int id)
 static int add_dport(struct cxl_port *port, struct cxl_dport *new)
 {
        struct cxl_dport *dup;
+       int rc;
 
        device_lock_assert(&port->dev);
        dup = find_dport(port, new->port_id);
@@ -821,8 +822,14 @@ static int add_dport(struct cxl_port *port, struct cxl_dport *new)
                        dev_name(dup->dport));
                return -EBUSY;
        }
-       return xa_insert(&port->dports, (unsigned long)new->dport, new,
-                        GFP_KERNEL);
+
+       rc = xa_insert(&port->dports, (unsigned long)new->dport, new,
+                      GFP_KERNEL);
+       if (rc)
+               return rc;
+
+       port->nr_dports++;
+       return 0;
 }
 
 /*

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index c52465e..c0253de 100644 (file)
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -990,7 +990,14 @@ static int cxl_port_setup_targets(struct cxl_port *port,
        if (cxl_rr->nr_targets_set) {
                int i, distance;
 
-               distance = p->nr_targets / cxl_rr->nr_targets;
+               /*
+                * Passthrough ports impose no distance requirements between
+                * peers
+                */
+               if (port->nr_dports == 1)
+                       distance = 0;
+               else
+                       distance = p->nr_targets / cxl_rr->nr_targets;
                for (i = 0; i < cxl_rr->nr_targets_set; i++)
                        if (ep->dport == cxlsd->target[i]) {
                                rc = check_last_peer(cxled, ep, cxl_rr,

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 1164ad4..ac75554 100644 (file)
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -457,6 +457,7 @@ struct cxl_pmem_region {
  * @regions: cxl_region_ref instances, regions mapped by this port
  * @parent_dport: dport that points to this port in the parent
  * @decoder_ida: allocator for decoder ids
+ * @nr_dports: number of entries in @dports
  * @hdm_end: track last allocated HDM decoder instance for allocation ordering
  * @commit_end: cursor to track highest committed decoder for commit ordering
  * @component_reg_phys: component register capability base address (optional)
@@ -475,6 +476,7 @@ struct cxl_port {
        struct xarray regions;
        struct cxl_dport *parent_dport;
        struct ida decoder_ida;
+       int nr_dports;
        int hdm_end;
        int commit_end;
        resource_size_t component_reg_phys;