linux/drivers/cxl/mem.c

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright(c) 2022 Intel Corporation. All rights reserved. */
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/pci.h>

#include "cxlmem.h"
#include "cxlpci.h"

/**
 * DOC: cxl mem
 *
 * CXL memory endpoint devices and switches are CXL capable devices that are
 * participating in CXL.mem protocol. Their functionality builds on top of the
 * CXL.io protocol that allows enumerating and configuring components via
 * standard PCI mechanisms.
 *
 * The cxl_mem driver owns kicking off the enumeration of this CXL.mem
 * capability. With the detection of a CXL capable endpoint, the driver will
 * walk up to find the platform specific port it is connected to, and determine
 * if there are intervening switches in the path. If there are switches, a
 * secondary action is to enumerate those (implemented in cxl_core). Finally the
 * cxl_mem driver adds the device it is bound to as a CXL endpoint-port for use
 * in higher level operations.
 */

static void enable_suspend(void *data)
{
	cxl_mem_active_dec();
}

static void remove_debugfs(void *dentry)
{
	debugfs_remove_recursive(dentry);
}

static int cxl_mem_dpa_show(struct seq_file *file, void *data)
{
	struct device *dev = file->private;
	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);

	cxl_dpa_debug(file, cxlmd->cxlds);

	return 0;
}

static int cxl_mem_probe(struct device *dev)
{
	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
	struct cxl_port *parent_port;
	struct cxl_dport *dport;
	struct dentry *dentry;
	int rc;

	/*
	 * Someone is trying to reattach this device after it lost its port
	 * connection (an endpoint port previously registered by this memdev was
	 * disabled). This racy check is ok because if the port is still gone,
	 * no harm done, and if the port hierarchy comes back it will re-trigger
	 * this probe. Port rescan and memdev detach work share the same
	 * single-threaded workqueue.
	 */
	if (work_pending(&cxlmd->detach_work))
		return -EBUSY;

	dentry = cxl_debugfs_create_dir(dev_name(dev));
	debugfs_create_devm_seqfile(dev, "dpamem", dentry, cxl_mem_dpa_show);
	rc = devm_add_action_or_reset(dev, remove_debugfs, dentry);
	if (rc)
		return rc;

	rc = devm_cxl_enumerate_ports(cxlmd);
	if (rc)
		return rc;

	parent_port = cxl_mem_find_port(cxlmd, &dport);
	if (!parent_port) {
		dev_err(dev, "CXL port topology not found\n");
		return -ENXIO;
	}

	device_lock(&parent_port->dev);
	if (!parent_port->dev.driver) {
		dev_err(dev, "CXL port topology %s not enabled\n",
			dev_name(&parent_port->dev));
		rc = -ENXIO;
		goto unlock;
	}

	rc = devm_cxl_add_endpoint(cxlmd, dport);
unlock:
	device_unlock(&parent_port->dev);
	put_device(&parent_port->dev);
	if (rc)
		return rc;

	/*
	 * The kernel may be operating out of CXL memory on this device,
	 * there is no spec defined way to determine whether this device
	 * preserves contents over suspend, and there is no simple way
	 * to arrange for the suspend image to avoid CXL memory which
	 * would setup a circular dependency between PCI resume and save
	 * state restoration.
	 *
	 * TODO: support suspend when all the regions this device is
	 * hosting are locked and covered by the system address map,
	 * i.e. platform firmware owns restoring the HDM configuration
	 * that it locked.
	 */
	cxl_mem_active_inc();
	return devm_add_action_or_reset(dev, enable_suspend, NULL);
}

static struct cxl_driver cxl_mem_driver = {
	.name = "cxl_mem",
	.probe = cxl_mem_probe,
	.id = CXL_DEVICE_MEMORY_EXPANDER,
};

module_cxl_driver(cxl_mem_driver);

MODULE_LICENSE("GPL v2");
MODULE_IMPORT_NS(CXL);
MODULE_ALIAS_CXL(CXL_DEVICE_MEMORY_EXPANDER);
/*
 * create_endpoint() wants to validate port driver attach immediately after
 * endpoint registration.
 */
MODULE_SOFTDEP("pre: cxl_port");