On 22-01-23 16:31:29, Dan Williams wrote:
> So far the platorm level CXL resources have been enumerated by the
> cxl_acpi driver, and cxl_pci has gathered all the pre-requisite
> information it needs to fire up a cxl_mem driver. However, the first
> thing the cxl_mem driver will be tasked to do is validate that all the
> PCIe Switches in its ancestry also have CXL capabilities and an CXL.mem
> link established.
>
> Provide a common mechanism for a CXL.mem endpoint driver to enumerate
> all the ancestor CXL ports in the topology and validate CXL.mem
> connectivity.
>
> Multiple endpoints may end up racing to establish a shared port in the
> topology. This race is resolved via taking the device-lock on a parent
> CXL Port before establishing a new child. The winner of the race
> establishes the port, the loser simply registers its interest in the
> port via 'struct cxl_ep' place-holder reference.
>
> At endpoint teardown the same parent port lock is taken as 'struct
> cxl_ep' references are deleted. Last endpoint to drop its reference
> unregisters the port.
>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> drivers/cxl/acpi.c | 17 --
> drivers/cxl/core/port.c | 379 +++++++++++++++++++++++++++++++++++++++++++++++
> drivers/cxl/cxl.h | 20 ++
> 3 files changed, 400 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 683f2ca32c97..7bd53dc691ec 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -130,21 +130,6 @@ static int cxl_parse_cfmws(union acpi_subtable_headers *header, void *arg,
> return 0;
> }
>
> -static struct cxl_dport *find_dport_by_dev(struct cxl_port *port, struct device *dev)
> -{
> - struct cxl_dport *dport;
> -
> - cxl_device_lock(&port->dev);
> - list_for_each_entry(dport, &port->dports, list)
> - if (dport->dport == dev) {
> - cxl_device_unlock(&port->dev);
> - return dport;
> - }
> -
> - cxl_device_unlock(&port->dev);
> - return NULL;
> -}
> -
> __mock struct acpi_device *to_cxl_host_bridge(struct device *host,
> struct device *dev)
> {
> @@ -175,7 +160,7 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> if (!bridge)
> return 0;
>
> - dport = find_dport_by_dev(root_port, match);
> + dport = cxl_find_dport_by_dev(root_port, match);
> if (!dport) {
> dev_dbg(host, "host bridge expected and not found\n");
> return 0;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 26c3eb9180cd..cd95d9f8c624 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -7,6 +7,7 @@
> #include <linux/slab.h>
> #include <linux/idr.h>
> #include <cxlmem.h>
> +#include <cxlpci.h>
> #include <cxl.h>
> #include "core.h"
>
> @@ -267,10 +268,24 @@ struct cxl_decoder *to_cxl_decoder(struct device *dev)
> }
> EXPORT_SYMBOL_NS_GPL(to_cxl_decoder, CXL);
>
> +static void cxl_ep_release(struct cxl_ep *ep)
> +{
> + if (!ep)
> + return;
> + list_del(&ep->list);
> + put_device(ep->ep);
> + kfree(ep);
> +}
> +
> static void cxl_port_release(struct device *dev)
> {
> struct cxl_port *port = to_cxl_port(dev);
> + struct cxl_ep *ep, *_e;
>
> + cxl_device_lock(dev);
> + list_for_each_entry_safe(ep, _e, &port->endpoints, list)
> + cxl_ep_release(ep);
> + cxl_device_unlock(dev);
> ida_free(&cxl_port_ida, port->id);
> kfree(port);
> }
> @@ -361,6 +376,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
> port->component_reg_phys = component_reg_phys;
> ida_init(&port->decoder_ida);
> INIT_LIST_HEAD(&port->dports);
> + INIT_LIST_HEAD(&port->endpoints);
>
> device_initialize(dev);
> device_set_pm_not_required(dev);
> @@ -639,6 +655,369 @@ struct cxl_dport *devm_cxl_add_dport(struct cxl_port *port,
> }
> EXPORT_SYMBOL_NS_GPL(devm_cxl_add_dport, CXL);
>
> +static struct cxl_ep *find_ep(struct cxl_port *port, struct device *ep_dev)
> +{
> + struct cxl_ep *ep;
> +
> + device_lock_assert(&port->dev);
> + list_for_each_entry(ep, &port->endpoints, list)
> + if (ep->ep == ep_dev)
> + return ep;
> + return NULL;
> +}
> +
> +static int add_ep(struct cxl_port *port, struct cxl_ep *new)
> +{
> + struct cxl_ep *dup;
> +
> + cxl_device_lock(&port->dev);
> + if (port->dead) {
> + cxl_device_unlock(&port->dev);
> + return -ENXIO;
> + }
> + dup = find_ep(port, new->ep);
> + if (!dup)
> + list_add_tail(&new->list, &port->endpoints);
> + cxl_device_unlock(&port->dev);
> +
> + return dup ? -EEXIST : 0;
> +}
> +
> +/**
> + * cxl_add_ep - register an endpoint's interest in a port
> + * @port: a port in the endpoint's topology ancestry
> + * @ep_dev: device representing the endpoint
> + *
> + * Intermediate CXL ports are scanned based on the arrival of endpoints.
> + * When those endpoints depart the port can be destroyed once all
> + * endpoints that care about that port have been removed.
> + */
> +static int cxl_add_ep(struct cxl_port *port, struct device *ep_dev)
> +{
> + struct cxl_ep *ep;
> + int rc;
> +
> + ep = kzalloc(sizeof(*ep), GFP_KERNEL);
> + if (!ep)
> + return -ENOMEM;
> +
> + INIT_LIST_HEAD(&ep->list);
> + ep->ep = get_device(ep_dev);
> +
> + rc = add_ep(port, ep);
> + if (rc)
> + cxl_ep_release(ep);
> + return rc;
> +}
> +
> +struct cxl_find_port_ctx {
> + const struct device *dport_dev;
> + const struct cxl_port *parent_port;
> +};
> +
> +static int match_port_by_dport(struct device *dev, const void *data)
> +{
> + const struct cxl_find_port_ctx *ctx = data;
> + struct cxl_port *port;
> +
> + if (!is_cxl_port(dev))
> + return 0;
> + if (ctx->parent_port && dev->parent != &ctx->parent_port->dev)
> + return 0;
> +
> + port = to_cxl_port(dev);
> + return cxl_find_dport_by_dev(port, ctx->dport_dev) != NULL;
> +}
> +
> +static struct cxl_port *__find_cxl_port(struct cxl_find_port_ctx *ctx)
> +{
> + struct device *dev;
> +
> + if (!ctx->dport_dev)
> + return NULL;
> +
> + dev = bus_find_device(&cxl_bus_type, NULL, ctx, match_port_by_dport);
> + if (dev)
> + return to_cxl_port(dev);
> + return NULL;
> +}
> +
> +static struct cxl_port *find_cxl_port(struct device *dport_dev)
> +{
> + struct cxl_find_port_ctx ctx = {
> + .dport_dev = dport_dev,
> + };
> +
> + return __find_cxl_port(&ctx);
> +}
> +
> +static struct cxl_port *find_cxl_port_at(struct cxl_port *parent_port,
> + struct device *dport_dev)
> +{
> + struct cxl_find_port_ctx ctx = {
> + .dport_dev = dport_dev,
> + .parent_port = parent_port,
> + };
> +
> + return __find_cxl_port(&ctx);
> +}
> +
> +static struct device *grandparent(struct device *dev)
> +{
> + if (dev && dev->parent)
> + return dev->parent->parent;
> + return NULL;
> +}
> +
> +static void delete_switch_port(struct cxl_memdev *cxlmd, struct cxl_port *port,
> + struct list_head *dports)
> +{
> + struct cxl_dport *dport, *_d;
> +
> + dev_dbg(&cxlmd->dev, "delete %s\n", dev_name(&port->dev));
> + list_for_each_entry_safe(dport, _d, dports, list) {
> + devm_release_action(&port->dev, cxl_dport_unlink, dport);
> + devm_release_action(&port->dev, cxl_dport_remove, dport);
> + devm_kfree(&port->dev, dport);
> + }
> + devm_release_action(port->dev.parent, cxl_unlink_uport, port);
> + devm_release_action(port->dev.parent, unregister_port, port);
> +}
I'd drop the cxlmd argument here. Let the caller print the dev_dbg if it wants.
> +
> +static void cxl_remove_ep(void *data)
> +{
> + struct cxl_memdev *cxlmd = data;
> + struct device *iter;
> +
> + for (iter = &cxlmd->dev; iter; iter = grandparent(iter)) {
> + struct device *dport_dev = grandparent(iter);
> + struct cxl_port *port, *parent_port;
> + LIST_HEAD(reap_dports);
> + struct cxl_ep *ep;
> +
> + if (!dport_dev)
> + break;
> +
> + port = find_cxl_port(dport_dev);
> + if (!port || is_cxl_root(port)) {
> + put_device(&port->dev);
> + continue;
Is there ever a case that continue != break for this case? It seems to be this
deserves a WARN_ON(grandparent(iter)) or some such, but I'd be curious to see if
my understanding is off.
> + }
> +
> + parent_port = to_cxl_port(port->dev.parent);
> + cxl_device_lock(&parent_port->dev);
> + if (!parent_port->dev.driver) {
> + cxl_device_unlock(&parent_port->dev);
> + put_device(&port->dev);
> + continue;
Similar to above, the parent_port must still exist at this point and have a
driver bound, correct?
> + }
> +
> + cxl_device_lock(&port->dev);
> + ep = find_ep(port, &cxlmd->dev);
> + dev_dbg(&cxlmd->dev, "disconnect %s from %s\n",
> + ep ? dev_name(ep->ep) : "", dev_name(&port->dev));
> + cxl_ep_release(ep);
> + if (ep && !port->dead && list_empty(&port->endpoints) &&
> + !is_cxl_root(parent_port)) {
> + /*
> + * This was the last ep attached to a dynamically
> + * enumerated port. Block new cxl_add_ep() and garbage
> + * collect the port.
> + */
> + port->dead = true;
> + list_splice_init(&port->dports, &reap_dports);
> + }
> + cxl_device_unlock(&port->dev);
> +
> + if (!list_empty(&reap_dports))
> + delete_switch_port(cxlmd, port, &reap_dports);
I admit I tried to make all this simpler and couldn't figure anything better
out.
> + put_device(&port->dev);
> + cxl_device_unlock(&parent_port->dev);
> + }
> +}
> +
> +static resource_size_t find_component_registers(struct device *dev)
> +{
> + struct cxl_register_map map;
> + struct pci_dev *pdev;
> +
> + /*
> + * Theoretically, CXL component registers can be hosted on a
I believe this is factually incorrect. The spec requires it be on a PCIe device.
Does it make sense to introduce a dev_is_cxltest()?
> + * non-PCI device, in practice, only cxl_test hits this case.
> + */
> + if (!dev_is_pci(dev))
> + return CXL_RESOURCE_NONE;
> +
> + pdev = to_pci_dev(dev);
> +
> + cxl_find_regblock(pdev, CXL_REGLOC_RBI_COMPONENT, &map);
> + return cxl_regmap_to_base(pdev, &map);
> +}
> +
> +static int add_port_register_ep(struct cxl_memdev *cxlmd,
> + struct device *uport_dev,
> + struct device *dport_dev)
> +{
> + struct cxl_port *port, *parent_port;
> + resource_size_t component_reg_phys;
> + int rc;
> +
> + parent_port = find_cxl_port(grandparent(dport_dev));
This is confusing (thought correct). dport's parent is a port, and port's parent
is a port. Logically though, I'd expect a grandparent of a device to be of the
same type. I wonder if there is some way to straighten that out, or if I'm the
only one that finds it confusing.
> + if (!parent_port) {
> + /*
> + * The root CXL port is added by the CXL platform driver, fail
> + * for now to be re-probed after platform driver attaches.
> + */
> + if (!grandparent(dport_dev)) {
> + dev_dbg(&cxlmd->dev, "%s is a root dport\n",
> + dev_name(dport_dev));
> + return -ENXIO;
> + }
> + /* ...otherwise, iterate to create this parent_port */
> + return -EAGAIN;
> + }
> +
> + cxl_device_lock(&parent_port->dev);
> + if (!parent_port->dev.driver) {
> + dev_warn(&cxlmd->dev,
> + "port %s:%s disabled, failed to enumerate CXL.mem\n",
> + dev_name(&parent_port->dev), dev_name(uport_dev));
> + rc = -ENXIO;
> + goto out;
> + }
> +
> + port = find_cxl_port_at(parent_port, dport_dev);
Again this is a bit tough on the terminology. A dport's parent is a port, but
not parent_port. I'd definitely suggest a comment for clarifying that.
> + if (!port) {
> + component_reg_phys = find_component_registers(uport_dev);
> + port = devm_cxl_add_port(&parent_port->dev, uport_dev,
> + component_reg_phys, parent_port);
> + if (!IS_ERR(port))
> + get_device(&port->dev);
> + }
> +out:
> + cxl_device_unlock(&parent_port->dev);
> +
> + if (IS_ERR(port))
> + rc = PTR_ERR(port);
> + else {
> + dev_dbg(&cxlmd->dev, "add to new port %s:%s\n",
> + dev_name(&port->dev), dev_name(port->uport));
> + rc = cxl_add_ep(port, &cxlmd->dev);
> + if (rc == -EEXIST) {
> + /*
> + * "can't" happen, but this error code means
> + * something to the caller, so translate it.
> + */
> + rc = -ENXIO;
"can't" should translate to a WARN IMHO.
> + }
> + put_device(&port->dev);
> + }
> +
> + put_device(&parent_port->dev);
> + return rc;
> +}
> +
> +int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
> +{
> + struct device *dev = &cxlmd->dev;
> + struct device *iter;
> + int rc;
> +
> + rc = devm_add_action_or_reset(&cxlmd->dev, cxl_remove_ep, cxlmd);
> + if (rc)
> + return rc;
> +
> + /*
> + * Scan for and add all cxl_ports in this device's ancestry.
> + * Repeat until no more ports are added. Abort if a port add
> + * attempt fails.
> + */
> +retry:
> + for (iter = dev; iter; iter = grandparent(iter)) {
> + struct device *dport_dev = grandparent(iter);
> + struct device *uport_dev;
> + struct cxl_port *port;
> +
> + if (!dport_dev)
> + break;
> + uport_dev = dport_dev->parent;
> + dev_dbg(dev, "scan: iter: %s dport_dev: %s parent: %s\n",
> + dev_name(iter), dev_name(dport_dev),
> + uport_dev ? dev_name(uport_dev) : "'none'");
> + if (!uport_dev) {
> + dev_warn(dev, "unexpected topology, no parent for %s\n",
> + dev_name(dport_dev));
> + rc = -ENXIO;
> + break;
> + }
> +
> + port = find_cxl_port(dport_dev);
> + if (port) {
> + dev_dbg(&cxlmd->dev,
> + "found already registered port %s:%s\n",
> + dev_name(&port->dev), dev_name(port->uport));
> + rc = cxl_add_ep(port, &cxlmd->dev);
> +
> + /*
> + * If the endpoint already exists in the port's list,
> + * that's ok, it was added on a previous pass.
> + * Otherwise, retry in add_port_register_ep() after
> + * taking the parent_port lock as the current port may
> + * be being reaped.
> + */
> + if (rc && rc != -EEXIST) {
> + put_device(&port->dev);
> + return rc;
> + }
I could use an explanation on how an endpoint could have been added on a
previous pass. It seems like !list_empty(&ep->list) here would be a bug.
> +
> + if (is_cxl_port(port->dev.parent) &&
> + !is_cxl_root(to_cxl_port(port->dev.parent))) {
> + put_device(&port->dev);
> + continue;
> + }
> +
> + put_device(&port->dev);
> + break;
> + }
> +
> + rc = add_port_register_ep(cxlmd, uport_dev, dport_dev);
> + /* port missing, try to add parent */
> + if (rc == -EAGAIN)
> + continue;
> + /* failed to add ep or port */
> + if (rc)
> + return rc;
> + /* port added, new descendants possible, start over */
> + goto retry;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_cxl_enumerate_ports, CXL);
> +
> +struct cxl_port *cxl_mem_find_port(struct cxl_memdev *cxlmd)
> +{
> + return find_cxl_port(grandparent(&cxlmd->dev));
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_mem_find_port, CXL);
> +
> +struct cxl_dport *cxl_find_dport_by_dev(struct cxl_port *port,
> + const struct device *dev)
> +{
> + struct cxl_dport *dport;
> +
> + cxl_device_lock(&port->dev);
> + list_for_each_entry(dport, &port->dports, list)
> + if (dport->dport == dev) {
> + cxl_device_unlock(&port->dev);
> + return dport;
> + }
> +
> + cxl_device_unlock(&port->dev);
> + return NULL;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_find_dport_by_dev, CXL);
> +
> static int decoder_populate_targets(struct cxl_decoder *cxld,
> struct cxl_port *port, int *target_map)
> {
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 7c714e559e95..b71d40b68ccd 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -262,8 +262,10 @@ struct cxl_nvdimm {
> * @uport: PCI or platform device implementing the upstream port capability
> * @id: id for port device-name
> * @dports: cxl_dport instances referenced by decoders
> + * @endpoints: cxl_ep instances, endpoints that are a descendant of this port
> * @decoder_ida: allocator for decoder ids
> * @component_reg_phys: component register capability base address (optional)
> + * @dead: last ep has been removed, force port re-creation
> * @depth: How deep this port is relative to the root. depth 0 is the root.
> */
> struct cxl_port {
> @@ -271,8 +273,10 @@ struct cxl_port {
> struct device *uport;
> int id;
> struct list_head dports;
> + struct list_head endpoints;
> struct ida decoder_ida;
> resource_size_t component_reg_phys;
> + bool dead;
> unsigned int depth;
> };
>
> @@ -292,6 +296,16 @@ struct cxl_dport {
> struct list_head list;
> };
>
> +/**
> + * struct cxl_ep - track an endpoint's interest in a port
> + * @ep: device that hosts a generic CXL endpoint (expander or accelerator)
> + * @list: node on port->endpoints list
> + */
> +struct cxl_ep {
> + struct device *ep;
> + struct list_head list;
> +};
> +
> static inline bool is_cxl_root(struct cxl_port *port)
> {
> return port->uport == port->dev.parent;
> @@ -307,9 +321,15 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> resource_size_t component_reg_phys,
> struct cxl_port *parent_port);
> struct cxl_port *find_cxl_root(struct device *dev);
> +int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
> +int cxl_bus_rescan(void);
> +
> struct cxl_dport *devm_cxl_add_dport(struct cxl_port *port,
> struct device *dport, int port_id,
> resource_size_t component_reg_phys);
> +struct cxl_dport *cxl_find_dport_by_dev(struct cxl_port *port,
> + const struct device *dev);
> +
> struct cxl_decoder *to_cxl_decoder(struct device *dev);
> bool is_root_decoder(struct device *dev);
> bool is_cxl_decoder(struct device *dev);
>
