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

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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: 27b3f8d138 ("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>
This commit is contained in:
Dan Williams 2022-11-03 17:30:54 -07:00
parent e41c8452b9
commit e4f6dfa9ef
3 changed files with 19 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
drivers/cxl/core/port.c
View File

@ -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;
}
/*

9
drivers/cxl/core/region.c
View File

@ -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,

2
drivers/cxl/cxl.h
View File

@ -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;