cxl/port: Cleanup handling of the nr_dports 0 -> 1 transition

There are multiple setup actions that can occur for a switch port after it
is known that it has at least one active downstream link. That work is
currently split between __devm_cxl_add_dport(), the add_dport() helper, and
cxl_port_add_dport() where decoder setup occurs.

Clean this up by moving all @dport object setup responsibilities into
add_dport() and all port effects into cxl_port_add_dport().

add_dport() handles taking a reference on @dport->dport_dev, and
cxl_port_add_dport() grows the awareness to setup the port component
registers. This removes an awkward open-coded xa_erase() from the middle of
__devm_cxl_add_dport() and instead tasks cxl_port_add_dport() with calling
the common @dport destruction path if anything goes wrong.

After this @port->nr_dports is always the count of @dports in the
@port->dports xarray, and cxl_dport_remove() is symmetric with add_dport().
With ->nr_dports now reliably tracking the number of dports the use of
ida_is_empty() can be dropped. Recall that the ida is only cleared on
"release" of decoder objects, and release can be arbitrarily delayed past
unregistration.

Lastly port->component_reg_phys is no longer reset to CXL_RESOURCE_NONE
post setup, no reason is seen to carry that forward.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Tested-by: Terry Bowman <terry.bowman@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20260131000403.2135324-2-dan.j.williams@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index fef3aa0c6680c0308d68e12794cc2ee3bfc507d8..ff899c690d85d00022efdd3ab6dee04674241f79 100644 (file)
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1066,11 +1066,15 @@ static int add_dport(struct cxl_port *port, struct cxl_dport *dport)
                return -EBUSY;
        }
 
+       /* Arrange for dport_dev to be valid through remove_dport() */
+       struct device *dev __free(put_device) = get_device(dport->dport_dev);
+
        rc = xa_insert(&port->dports, (unsigned long)dport->dport_dev, dport,
                       GFP_KERNEL);
        if (rc)
                return rc;
 
+       retain_and_null_ptr(dev);
        port->nr_dports++;
        return 0;
 }
@@ -1099,6 +1103,7 @@ static void cxl_dport_remove(void *data)
        struct cxl_dport *dport = data;
        struct cxl_port *port = dport->port;
 
+       port->nr_dports--;
        xa_erase(&port->dports, (unsigned long) dport->dport_dev);
        put_device(dport->dport_dev);
 }
@@ -1181,21 +1186,6 @@ __devm_cxl_add_dport(struct cxl_port *port, struct device *dport_dev,
        if (rc)
                return ERR_PTR(rc);
 
-       /*
-        * Setup port register if this is the first dport showed up. Having
-        * a dport also means that there is at least 1 active link.
-        */
-       if (port->nr_dports == 1 &&
-           port->component_reg_phys != CXL_RESOURCE_NONE) {
-               rc = cxl_port_setup_regs(port, port->component_reg_phys);
-               if (rc) {
-                       xa_erase(&port->dports, (unsigned long)dport->dport_dev);
-                       return ERR_PTR(rc);
-               }
-               port->component_reg_phys = CXL_RESOURCE_NONE;
-       }
-
-       get_device(dport_dev);
        rc = devm_add_action_or_reset(host, cxl_dport_remove, dport);
        if (rc)
                return ERR_PTR(rc);
@@ -1622,7 +1612,16 @@ static struct cxl_dport *cxl_port_add_dport(struct cxl_port *port,
 
        cxl_switch_parse_cdat(new_dport);
 
-       if (ida_is_empty(&port->decoder_ida)) {
+       if (port->nr_dports == 1) {
+               /*
+                * Some host bridges are known to not have component regsisters
+                * available until a root port has trained CXL. Perform that
+                * setup now.
+                */
+               rc = cxl_port_setup_regs(port, port->component_reg_phys);
+               if (rc)
+                       return ERR_PTR(rc);
+
                rc = devm_cxl_switch_port_decoders_setup(port);
                if (rc)
                        return ERR_PTR(rc);