[PATCH 2/5] PCI/DOE: Add Data Object Exchange Aux Driver

[ira.weiny@intel.com]

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Introduced in a PCI ECN [1], DOE provides a config space based mailbox
with standard protocol discovery.  Each mailbox is accessed through a
DOE Extended Capability.

Define an auxiliary device driver which control DOE auxiliary devices
registered on the auxiliary bus.

A DOE mailbox is allowed to support any number of protocols while some
DOE protocol specifications apply additional restrictions.

The protocols supported are queried and cached.  pci_doe_supports_prot()
can be used to determine if the DOE device supports the protocol
specified.

A synchronous interface is provided in pci_doe_exchange_sync() to
perform a single query / response exchange from the driver through the
device specified.

Testing was conducted against QEMU using:

https://lore.kernel.org/qemu-devel/1619454964-10190-1-git-send-email-cbrowy@avery-design.com/

This code is based on Jonathan's V4 series here:

https://lore.kernel.org/linux-cxl/20210524133938.2815206-1-Jonathan.Cameron@huawei.com/

[1] https://members.pcisig.com/wg/PCI-SIG/document/14143
    Data Object Exchange (DOE) - Approved 12 March 2020

Co-developed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
Changes from Jonathan's V4
	Move the DOE MB code into the DOE auxiliary driver
	Remove Task List in favor of a wait queue

Changes from Ben
	remove CXL references
	propagate rc from pci functions on error
---
 drivers/pci/Kconfig           |  10 +
 drivers/pci/Makefile          |   3 +
 drivers/pci/doe.c             | 701 ++++++++++++++++++++++++++++++++++
 include/linux/pci-doe.h       |  63 +++
 include/uapi/linux/pci_regs.h |  29 +-
 5 files changed, 805 insertions(+), 1 deletion(-)
 create mode 100644 drivers/pci/doe.c
 create mode 100644 include/linux/pci-doe.h

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 0c473d75e625..b512295538ba 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -118,6 +118,16 @@ config XEN_PCIDEV_FRONTEND
 	  The PCI device frontend driver allows the kernel to import arbitrary
 	  PCI devices from a PCI backend to support PCI driver domains.
 
+config PCI_DOE_DRIVER
+	tristate "PCI Data Object Exchange (DOE) driver"
+	select AUXILIARY_BUS
+	help
+	  Driver for DOE auxiliary devices.
+
+	  DOE provides a simple mailbox in PCI config space that is used by a
+	  number of different protocols.  DOE is defined in the Data Object
+	  Exchange ECN to the PCIe r5.0 spec.
+
 config PCI_ATS
 	bool
 
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index d62c4ac4ae1b..afd9d7bd2b82 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -28,8 +28,11 @@ obj-$(CONFIG_PCI_STUB)		+= pci-stub.o
 obj-$(CONFIG_PCI_PF_STUB)	+= pci-pf-stub.o
 obj-$(CONFIG_PCI_ECAM)		+= ecam.o
 obj-$(CONFIG_PCI_P2PDMA)	+= p2pdma.o
+obj-$(CONFIG_PCI_DOE_DRIVER)	+= pci-doe.o
 obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
 
+pci-doe-y := doe.o
+
 # Endpoint library must be initialized before its users
 obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/
 
diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
new file mode 100644
index 000000000000..2e702fdc7879
--- /dev/null
+++ b/drivers/pci/doe.c
@@ -0,0 +1,701 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Data Object Exchange ECN
+ * https://members.pcisig.com/wg/PCI-SIG/document/14143
+ *
+ * Copyright (C) 2021 Huawei
+ *     Jonathan Cameron <Jonathan.Cameron@huawei.com>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/jiffies.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/pci.h>
+#include <linux/pci-doe.h>
+#include <linux/workqueue.h>
+#include <linux/module.h>
+
+#define PCI_DOE_PROTOCOL_DISCOVERY 0
+
+#define PCI_DOE_BUSY_MAX_RETRIES 16
+#define PCI_DOE_POLL_INTERVAL (HZ / 128)
+
+/* Timeout of 1 second from 6.xx.1 (Operation), ECN - Data Object Exchange */
+#define PCI_DOE_TIMEOUT HZ
+
+enum pci_doe_state {
+	DOE_IDLE,
+	DOE_WAIT_RESP,
+	DOE_WAIT_ABORT,
+	DOE_WAIT_ABORT_ON_ERR,
+};
+
+/*
+ * struct pci_doe_task - description of a query / response task
+ * @ex: The details of the task to be done
+ * @rv: Return value.  Length of received response or error
+ * @cb: Callback for completion of task
+ * @private: Private data passed to callback on completion
+ */
+struct pci_doe_task {
+	struct pci_doe_exchange *ex;
+	int rv;
+	void (*cb)(void *private);
+	void *private;
+};
+
+/**
+ * struct pci_doe - A single DOE mailbox driver
+ *
+ * @doe_dev: The DOE Auxiliary device being driven
+ * @abort_c: Completion used for initial abort handling
+ * @irq: Interrupt used for signaling DOE ready or abort
+ * @irq_name: Name used to identify the irq for a particular DOE
+ * @prots: Array of identifiers for protocols supported
+ * @num_prots: Size of prots array
+ * @cur_task: Current task the state machine is working on
+ * @wq: Wait queue to wait on if a query is in progress
+ * @state_lock: Protect the state of cur_task, abort, and dead
+ * @statemachine: Work item for the DOE state machine
+ * @state: Current state of this DOE
+ * @timeout_jiffies: 1 second after GO set
+ * @busy_retries: Count of retry attempts
+ * @abort: Request a manual abort (e.g. on init)
+ * @dead: Used to mark a DOE for which an ABORT has timed out. Further messages
+ *        will immediately be aborted with error
+ */
+struct pci_doe {
+	struct pci_doe_dev *doe_dev;
+	struct completion abort_c;
+	int irq;
+	char *irq_name;
+	struct pci_doe_protocol *prots;
+	int num_prots;
+
+	struct pci_doe_task *cur_task;
+	wait_queue_head_t wq;
+	struct mutex state_lock;
+	struct delayed_work statemachine;
+	enum pci_doe_state state;
+	unsigned long timeout_jiffies;
+	unsigned int busy_retries;
+	unsigned int abort:1;
+	unsigned int dead:1;
+};
+
+static irqreturn_t pci_doe_irq(int irq, void *data)
+{
+	struct pci_doe *doe = data;
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	int offset = doe->doe_dev->cap_offset;
+	u32 val;
+
+	pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
+	if (FIELD_GET(PCI_DOE_STATUS_INT_STATUS, val)) {
+		pci_write_config_dword(pdev, offset + PCI_DOE_STATUS, val);
+		mod_delayed_work(system_wq, &doe->statemachine, 0);
+		return IRQ_HANDLED;
+	}
+	/* Leave the error case to be handled outside IRQ */
+	if (FIELD_GET(PCI_DOE_STATUS_ERROR, val)) {
+		mod_delayed_work(system_wq, &doe->statemachine, 0);
+		return IRQ_HANDLED;
+	}
+
+	/*
+	 * Busy being cleared can result in an interrupt, but as
+	 * the original Busy may not have been detected, there is no
+	 * way to separate such an interrupt from a spurious interrupt.
+	 */
+	return IRQ_HANDLED;
+}
+
+/*
+ * Only call when safe to directly access the DOE, either because no tasks yet
+ * queued, or called from doe_statemachine_work() which has exclusive access to
+ * the DOE config space.
+ */
+static void pci_doe_abort_start(struct pci_doe *doe)
+{
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	int offset = doe->doe_dev->cap_offset;
+	u32 val;
+
+	val = PCI_DOE_CTRL_ABORT;
+	if (doe->irq)
+		val |= PCI_DOE_CTRL_INT_EN;
+	pci_write_config_dword(pdev, offset + PCI_DOE_CTRL, val);
+
+	doe->timeout_jiffies = jiffies + HZ;
+	schedule_delayed_work(&doe->statemachine, HZ);
+}
+
+static int pci_doe_send_req(struct pci_doe *doe, struct pci_doe_exchange *ex)
+{
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	int offset = doe->doe_dev->cap_offset;
+	u32 val;
+	int i;
+
+	/*
+	 * Check the DOE busy bit is not set. If it is set, this could indicate
+	 * someone other than Linux (e.g. firmware) is using the mailbox. Note
+	 * it is expected that firmware and OS will negotiate access rights via
+	 * an, as yet to be defined method.
+	 */
+	pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
+	if (FIELD_GET(PCI_DOE_STATUS_BUSY, val))
+		return -EBUSY;
+
+	if (FIELD_GET(PCI_DOE_STATUS_ERROR, val))
+		return -EIO;
+
+	/* Write DOE Header */
+	val = FIELD_PREP(PCI_DOE_DATA_OBJECT_HEADER_1_VID, ex->prot.vid) |
+		FIELD_PREP(PCI_DOE_DATA_OBJECT_HEADER_1_TYPE, ex->prot.type);
+	pci_write_config_dword(pdev, offset + PCI_DOE_WRITE, val);
+	/* Length is 2 DW of header + length of payload in DW */
+	pci_write_config_dword(pdev, offset + PCI_DOE_WRITE,
+			       FIELD_PREP(PCI_DOE_DATA_OBJECT_HEADER_2_LENGTH,
+					  2 + ex->request_pl_sz / sizeof(u32)));
+	for (i = 0; i < ex->request_pl_sz / sizeof(u32); i++)
+		pci_write_config_dword(pdev, offset + PCI_DOE_WRITE,
+				       ex->request_pl[i]);
+
+	val = PCI_DOE_CTRL_GO;
+	if (doe->irq)
+		val |= PCI_DOE_CTRL_INT_EN;
+
+	pci_write_config_dword(pdev, offset + PCI_DOE_CTRL, val);
+	/* Request is sent - now wait for poll or IRQ */
+	return 0;
+}
+
+static int pci_doe_recv_resp(struct pci_doe *doe, struct pci_doe_exchange *ex)
+{
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	int offset = doe->doe_dev->cap_offset;
+	size_t length;
+	u32 val;
+	int i;
+
+	/* Read the first dword to get the protocol */
+	pci_read_config_dword(pdev, offset + PCI_DOE_READ, &val);
+	if ((FIELD_GET(PCI_DOE_DATA_OBJECT_HEADER_1_VID, val) != ex->prot.vid) ||
+	    (FIELD_GET(PCI_DOE_DATA_OBJECT_HEADER_1_TYPE, val) != ex->prot.type)) {
+		pci_err(pdev,
+			"Expected [VID, Protocol] = [%x, %x], got [%x, %x]\n",
+			ex->prot.vid, ex->prot.type,
+			FIELD_GET(PCI_DOE_DATA_OBJECT_HEADER_1_VID, val),
+			FIELD_GET(PCI_DOE_DATA_OBJECT_HEADER_1_TYPE, val));
+		return -EIO;
+	}
+
+	pci_write_config_dword(pdev, offset + PCI_DOE_READ, 0);
+	/* Read the second dword to get the length */
+	pci_read_config_dword(pdev, offset + PCI_DOE_READ, &val);
+	pci_write_config_dword(pdev, offset + PCI_DOE_READ, 0);
+
+	length = FIELD_GET(PCI_DOE_DATA_OBJECT_HEADER_2_LENGTH, val);
+	if (length > SZ_1M || length < 2)
+		return -EIO;
+
+	/* First 2 dwords have already been read */
+	length -= 2;
+	/* Read the rest of the response payload */
+	for (i = 0; i < min(length, ex->response_pl_sz / sizeof(u32)); i++) {
+		pci_read_config_dword(pdev, offset + PCI_DOE_READ,
+				      &ex->response_pl[i]);
+		pci_write_config_dword(pdev, offset + PCI_DOE_READ, 0);
+	}
+
+	/* Flush excess length */
+	for (; i < length; i++) {
+		pci_read_config_dword(pdev, offset + PCI_DOE_READ, &val);
+		pci_write_config_dword(pdev, offset + PCI_DOE_READ, 0);
+	}
+	/* Final error check to pick up on any since Data Object Ready */
+	pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
+	if (FIELD_GET(PCI_DOE_STATUS_ERROR, val))
+		return -EIO;
+
+	return min(length, ex->response_pl_sz / sizeof(u32)) * sizeof(u32);
+}
+
+static void pci_doe_task_complete(void *private)
+{
+	complete(private);
+}
+
+static void doe_statemachine_work(struct work_struct *work)
+{
+	struct delayed_work *w = to_delayed_work(work);
+	struct pci_doe *doe = container_of(w, struct pci_doe, statemachine);
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	int offset = doe->doe_dev->cap_offset;
+	struct pci_doe_task *task;
+	bool abort;
+	u32 val;
+	int rc;
+
+	mutex_lock(&doe->state_lock);
+	task = doe->cur_task;
+	abort = doe->abort;
+	doe->abort = false;
+	mutex_unlock(&doe->state_lock);
+
+	if (abort) {
+		/*
+		 * Currently only used during init - care needed if
+		 * pci_doe_abort() is generally exposed as it would impact
+		 * queries in flight.
+		 */
+		WARN_ON(task);
+		doe->state = DOE_WAIT_ABORT;
+		pci_doe_abort_start(doe);
+		return;
+	}
+
+	switch (doe->state) {
+	case DOE_IDLE:
+		if (task == NULL)
+			return;
+
+		/* Nothing currently in flight so queue a task */
+		rc = pci_doe_send_req(doe, task->ex);
+		/*
+		 * The specification does not provide any guidance on how long
+		 * some other entity could keep the DOE busy, so try for 1
+		 * second then fail. Busy handling is best effort only, because
+		 * there is no way of avoiding racing against another user of
+		 * the DOE.
+		 */
+		if (rc == -EBUSY) {
+			doe->busy_retries++;
+			if (doe->busy_retries == PCI_DOE_BUSY_MAX_RETRIES) {
+				/* Long enough, fail this request */
+				pci_WARN(pdev, true, "DOE busy for too long\n");
+				doe->busy_retries = 0;
+				goto err_busy;
+			}
+			schedule_delayed_work(w, HZ / PCI_DOE_BUSY_MAX_RETRIES);
+			return;
+		}
+		if (rc)
+			goto err_abort;
+		doe->busy_retries = 0;
+
+		doe->state = DOE_WAIT_RESP;
+		doe->timeout_jiffies = jiffies + HZ;
+		/* Now poll or wait for IRQ with timeout */
+		if (doe->irq > 0)
+			schedule_delayed_work(w, PCI_DOE_TIMEOUT);
+		else
+			schedule_delayed_work(w, PCI_DOE_POLL_INTERVAL);
+		return;
+
+	case DOE_WAIT_RESP:
+		/* Not possible to get here with NULL task */
+		pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
+		if (FIELD_GET(PCI_DOE_STATUS_ERROR, val)) {
+			rc = -EIO;
+			goto err_abort;
+		}
+
+		if (!FIELD_GET(PCI_DOE_STATUS_DATA_OBJECT_READY, val)) {
+			/* If not yet at timeout reschedule otherwise abort */
+			if (time_after(jiffies, doe->timeout_jiffies)) {
+				rc = -ETIMEDOUT;
+				goto err_abort;
+			}
+			schedule_delayed_work(w, PCI_DOE_POLL_INTERVAL);
+			return;
+		}
+
+		rc  = pci_doe_recv_resp(doe, task->ex);
+		if (rc < 0)
+			goto err_abort;
+
+		doe->state = DOE_IDLE;
+
+		mutex_lock(&doe->state_lock);
+		doe->cur_task = NULL;
+		mutex_unlock(&doe->state_lock);
+		wake_up_interruptible(&doe->wq);
+
+		/* Set the return value to the length of received payload */
+		task->rv = rc;
+		task->cb(task->private);
+
+		return;
+
+	case DOE_WAIT_ABORT:
+	case DOE_WAIT_ABORT_ON_ERR:
+		pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
+
+		if (!FIELD_GET(PCI_DOE_STATUS_ERROR, val) &&
+		    !FIELD_GET(PCI_DOE_STATUS_BUSY, val)) {
+			/* Back to normal state - carry on */
+			mutex_lock(&doe->state_lock);
+			doe->cur_task = NULL;
+			mutex_unlock(&doe->state_lock);
+			wake_up_interruptible(&doe->wq);
+
+			/*
+			 * For deliberately triggered abort, someone is
+			 * waiting.
+			 */
+			if (doe->state == DOE_WAIT_ABORT)
+				complete(&doe->abort_c);
+
+			doe->state = DOE_IDLE;
+			return;
+		}
+		if (time_after(jiffies, doe->timeout_jiffies)) {
+			/* Task has timed out and is dead - abort */
+			pci_err(pdev, "DOE ABORT timed out\n");
+			mutex_lock(&doe->state_lock);
+			doe->dead = true;
+			doe->cur_task = NULL;
+			mutex_unlock(&doe->state_lock);
+			wake_up_interruptible(&doe->wq);
+
+			if (doe->state == DOE_WAIT_ABORT)
+				complete(&doe->abort_c);
+		}
+		return;
+	}
+
+err_abort:
+	doe->state = DOE_WAIT_ABORT_ON_ERR;
+	pci_doe_abort_start(doe);
+err_busy:
+	task->rv = rc;
+	task->cb(task->private);
+	/* If here via err_busy, signal the task done. */
+	if (doe->state == DOE_IDLE) {
+		mutex_lock(&doe->state_lock);
+		doe->cur_task = NULL;
+		mutex_unlock(&doe->state_lock);
+		wake_up_interruptible(&doe->wq);
+	}
+}
+
+/**
+ * pci_doe_exchange_sync() - Send a request, then wait for and receive a response
+ * @doe: DOE mailbox state structure
+ * @ex: Description of the buffers and Vendor ID + type used in this
+ *      request/response pair
+ *
+ * Excess data will be discarded.
+ *
+ * RETURNS: payload in bytes on success, < 0 on error
+ */
+int pci_doe_exchange_sync(struct pci_doe_dev *doe_dev, struct pci_doe_exchange *ex)
+{
+	struct pci_doe *doe = dev_get_drvdata(&doe_dev->adev.dev);
+	struct pci_doe_task task;
+	DECLARE_COMPLETION_ONSTACK(c);
+
+	if (!doe)
+		return -EAGAIN;
+
+	/* DOE requests must be a whole number of DW */
+	if (ex->request_pl_sz % sizeof(u32))
+		return -EINVAL;
+
+	task.ex = ex;
+	task.cb = pci_doe_task_complete;
+	task.private = &c;
+
+again:
+	mutex_lock(&doe->state_lock);
+	if (doe->cur_task) {
+		mutex_unlock(&doe->state_lock);
+		wait_event_interruptible(doe->wq, doe->cur_task == NULL);
+		goto again;
+	}
+
+	if (doe->dead) {
+		mutex_unlock(&doe->state_lock);
+		return -EIO;
+	}
+	doe->cur_task = &task;
+	schedule_delayed_work(&doe->statemachine, 0);
+	mutex_unlock(&doe->state_lock);
+
+	wait_for_completion(&c);
+
+	return task.rv;
+}
+EXPORT_SYMBOL_GPL(pci_doe_exchange_sync);
+
+/**
+ * pci_doe_supports_prot() - Return if the DOE instance supports the given protocol
+ * @pdev: Device on which to find the DOE instance
+ * @vid: Protocol Vendor ID
+ * @type: protocol type
+ *
+ * This device can then be passed to pci_doe_exchange_sync() to execute a mailbox
+ * exchange through that DOE mailbox.
+ *
+ * RETURNS: True if the DOE device supports the protocol specified
+ */
+bool pci_doe_supports_prot(struct pci_doe_dev *doe_dev, u16 vid, u8 type)
+{
+	struct pci_doe *doe = dev_get_drvdata(&doe_dev->adev.dev);
+	int i;
+
+	if (!doe)
+		return false;
+
+	for (i = 0; i < doe->num_prots; i++)
+		if ((doe->prots[i].vid == vid) &&
+		    (doe->prots[i].type == type))
+			return true;
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(pci_doe_supports_prot);
+
+static int pci_doe_discovery(struct pci_doe *doe, u8 *index, u16 *vid,
+			     u8 *protocol)
+{
+	u32 request_pl = FIELD_PREP(PCI_DOE_DATA_OBJECT_DISC_REQ_3_INDEX, *index);
+	u32 response_pl;
+	struct pci_doe_exchange ex = {
+		.prot.vid = PCI_VENDOR_ID_PCI_SIG,
+		.prot.type = PCI_DOE_PROTOCOL_DISCOVERY,
+		.request_pl = &request_pl,
+		.request_pl_sz = sizeof(request_pl),
+		.response_pl = &response_pl,
+		.response_pl_sz = sizeof(response_pl),
+	};
+	int ret;
+
+	ret = pci_doe_exchange_sync(doe->doe_dev, &ex);
+	if (ret < 0)
+		return ret;
+
+	if (ret != sizeof(response_pl))
+		return -EIO;
+
+	*vid = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_VID, response_pl);
+	*protocol = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL, response_pl);
+	*index = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX, response_pl);
+
+	return 0;
+}
+
+static int pci_doe_cache_protocols(struct pci_doe *doe)
+{
+	u8 index = 0;
+	int rc;
+
+	/* Discovery protocol must always be supported and must report itself */
+	doe->num_prots = 1;
+	doe->prots = kcalloc(doe->num_prots, sizeof(*doe->prots), GFP_KERNEL);
+	if (doe->prots == NULL)
+		return -ENOMEM;
+
+	do {
+		struct pci_doe_protocol *prot;
+
+		prot = &doe->prots[doe->num_prots - 1];
+		rc = pci_doe_discovery(doe, &index, &prot->vid, &prot->type);
+		if (rc)
+			goto err_free_prots;
+
+		if (index) {
+			struct pci_doe_protocol *prot_new;
+
+			doe->num_prots++;
+			prot_new = krealloc(doe->prots,
+					    sizeof(*doe->prots) * doe->num_prots,
+					    GFP_KERNEL);
+			if (prot_new == NULL) {
+				rc = -ENOMEM;
+				goto err_free_prots;
+			}
+			doe->prots = prot_new;
+		}
+	} while (index);
+
+	return 0;
+
+err_free_prots:
+	kfree(doe->prots);
+	doe->num_prots = 0;
+	doe->prots = NULL;
+	return rc;
+}
+
+static int pci_doe_abort(struct pci_doe *doe)
+{
+	reinit_completion(&doe->abort_c);
+	mutex_lock(&doe->state_lock);
+	doe->abort = true;
+	mutex_unlock(&doe->state_lock);
+	schedule_delayed_work(&doe->statemachine, 0);
+	wait_for_completion(&doe->abort_c);
+
+	if (doe->dead)
+		return -EIO;
+
+	return 0;
+}
+
+static void pci_doe_release_irq(struct pci_doe *doe)
+{
+	if (doe->irq > 0)
+		free_irq(doe->irq, doe);
+}
+
+static int pci_doe_register(struct pci_doe *doe)
+{
+	struct pci_dev *pdev = doe->doe_dev->pdev;
+	bool poll = !pci_dev_msi_enabled(pdev);
+	int offset = doe->doe_dev->cap_offset;
+	int rc, irq;
+	u32 val;
+
+	pci_read_config_dword(pdev, offset + PCI_DOE_CAP, &val);
+
+	if (!poll && FIELD_GET(PCI_DOE_CAP_INT, val)) {
+		irq = pci_irq_vector(pdev, FIELD_GET(PCI_DOE_CAP_IRQ, val));
+		if (irq < 0)
+			return irq;
+
+		doe->irq_name = kasprintf(GFP_KERNEL, "DOE[%s]",
+					  doe->doe_dev->adev.name);
+		if (!doe->irq_name)
+			return -ENOMEM;
+
+		rc = request_irq(irq, pci_doe_irq, 0, doe->irq_name, doe);
+		if (rc)
+			goto err_free_name;
+
+		doe->irq = irq;
+		pci_write_config_dword(pdev, offset + PCI_DOE_CTRL,
+				       PCI_DOE_CTRL_INT_EN);
+	}
+
+	/* Reset the mailbox by issuing an abort */
+	rc = pci_doe_abort(doe);
+	if (rc)
+		goto err_free_irqs;
+
+	/* Ensure the pci device remains until this driver is done with it */
+	get_device(&pdev->dev);
+
+	return 0;
+
+err_free_irqs:
+	pci_doe_release_irq(doe);
+err_free_name:
+	kfree(doe->irq_name);
+	return rc;
+}
+
+static void pci_doe_unregister(struct pci_doe *doe)
+{
+	pci_doe_release_irq(doe);
+	kfree(doe->irq_name);
+	put_device(&doe->doe_dev->pdev->dev);
+}
+
+/*
+ * pci_doe_probe() - Set up the Mailbox
+ * @aux_dev: Auxiliary Device
+ * @id: Auxiliary device ID
+ *
+ * Probe the mailbox found for all protocols and set up the Mailbox
+ *
+ * RETURNS: 0 on success, < 0 on error
+ */
+static int pci_doe_probe(struct auxiliary_device *aux_dev,
+			 const struct auxiliary_device_id *id)
+{
+	struct pci_doe_dev *doe_dev = container_of(aux_dev,
+					struct pci_doe_dev,
+					adev);
+	struct pci_doe *doe;
+	int rc;
+
+	doe = kzalloc(sizeof(*doe), GFP_KERNEL);
+	if (!doe)
+		return -ENOMEM;
+
+	mutex_init(&doe->state_lock);
+	init_completion(&doe->abort_c);
+	doe->doe_dev = doe_dev;
+	init_waitqueue_head(&doe->wq);
+	INIT_DELAYED_WORK(&doe->statemachine, doe_statemachine_work);
+	dev_set_drvdata(&aux_dev->dev, doe);
+
+	rc = pci_doe_register(doe);
+	if (rc)
+		goto err_free;
+
+	rc = pci_doe_cache_protocols(doe);
+	if (rc) {
+		pci_doe_unregister(doe);
+		goto err_free;
+	}
+
+	return 0;
+
+err_free:
+	kfree(doe);
+	return rc;
+}
+
+static void pci_doe_remove(struct auxiliary_device *aux_dev)
+{
+	struct pci_doe *doe = dev_get_drvdata(&aux_dev->dev);
+
+	/* First halt the state machine */
+	cancel_delayed_work_sync(&doe->statemachine);
+	kfree(doe->prots);
+	pci_doe_unregister(doe);
+	kfree(doe);
+}
+
+static const struct auxiliary_device_id pci_doe_auxiliary_id_table[] = {
+	{.name = "cxl_pci.doe", },
+	{},
+};
+
+MODULE_DEVICE_TABLE(auxiliary, pci_doe_auxiliary_id_table);
+
+struct auxiliary_driver pci_doe_auxiliary_drv = {
+	.name = "pci_doe_drv",
+	.id_table = pci_doe_auxiliary_id_table,
+	.probe = pci_doe_probe,
+	.remove = pci_doe_remove
+};
+
+static int __init pci_doe_init_module(void)
+{
+	int ret;
+
+	ret = auxiliary_driver_register(&pci_doe_auxiliary_drv);
+	if (ret) {
+		pr_err("Failed pci_doe auxiliary_driver_register() ret=%d\n",
+		       ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void __exit pci_doe_exit_module(void)
+{
+	auxiliary_driver_unregister(&pci_doe_auxiliary_drv);
+}
+
+module_init(pci_doe_init_module);
+module_exit(pci_doe_exit_module);
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/pci-doe.h b/include/linux/pci-doe.h
new file mode 100644
index 000000000000..8380b7ad33d4
--- /dev/null
+++ b/include/linux/pci-doe.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Data Object Exchange was added as an ECN to the PCIe r5.0 spec.
+ *
+ * Copyright (C) 2021 Huawei
+ *     Jonathan Cameron <Jonathan.Cameron@huawei.com>
+ */
+
+#include <linux/completion.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/auxiliary_bus.h>
+
+#ifndef LINUX_PCI_DOE_H
+#define LINUX_PCI_DOE_H
+
+#define DOE_DEV_NAME "doe"
+
+struct pci_doe_protocol {
+	u16 vid;
+	u8 type;
+};
+
+/**
+ * struct pci_doe_exchange - represents a single query/response
+ *
+ * @prot: DOE Protocol
+ * @request_pl: The request payload
+ * @request_pl_sz: Size of the request payload
+ * @response_pl: The response payload
+ * @response_pl_sz: Size of the response payload
+ */
+struct pci_doe_exchange {
+	struct pci_doe_protocol prot;
+	u32 *request_pl;
+	size_t request_pl_sz;
+	u32 *response_pl;
+	size_t response_pl_sz;
+};
+
+/**
+ * struct pci_doe_dev - DOE mailbox device
+ *
+ * @adrv: Auxiliary Driver data
+ * @pdev: PCI device this belongs to
+ * @offset: Capability offset
+ *
+ * This represents a single DOE mailbox device.  Devices should create this
+ * device and register it on the Auxiliary bus for the DOE driver to maintain.
+ *
+ */
+struct pci_doe_dev {
+	struct auxiliary_device adev;
+	struct pci_dev *pdev;
+	int cap_offset;
+};
+
+/* Library operations */
+int pci_doe_exchange_sync(struct pci_doe_dev *doe_dev,
+				 struct pci_doe_exchange *ex);
+bool pci_doe_supports_prot(struct pci_doe_dev *doe_dev, u16 vid, u8 type);
+
+#endif
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index e709ae8235e7..1073cd1916e1 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -730,7 +730,8 @@
 #define PCI_EXT_CAP_ID_DVSEC	0x23	/* Designated Vendor-Specific */
 #define PCI_EXT_CAP_ID_DLF	0x25	/* Data Link Feature */
 #define PCI_EXT_CAP_ID_PL_16GT	0x26	/* Physical Layer 16.0 GT/s */
-#define PCI_EXT_CAP_ID_MAX	PCI_EXT_CAP_ID_PL_16GT
+#define PCI_EXT_CAP_ID_DOE	0x2E	/* Data Object Exchange */
+#define PCI_EXT_CAP_ID_MAX	PCI_EXT_CAP_ID_DOE
 
 #define PCI_EXT_CAP_DSN_SIZEOF	12
 #define PCI_EXT_CAP_MCAST_ENDPOINT_SIZEOF 40
@@ -1092,4 +1093,30 @@
 #define  PCI_PL_16GT_LE_CTRL_USP_TX_PRESET_MASK		0x000000F0
 #define  PCI_PL_16GT_LE_CTRL_USP_TX_PRESET_SHIFT	4
 
+/* Data Object Exchange */
+#define PCI_DOE_CAP            0x04    /* DOE Capabilities Register */
+#define  PCI_DOE_CAP_INT                       0x00000001  /* Interrupt Support */
+#define  PCI_DOE_CAP_IRQ                       0x00000ffe  /* Interrupt Message Number */
+#define PCI_DOE_CTRL           0x08    /* DOE Control Register */
+#define  PCI_DOE_CTRL_ABORT                    0x00000001  /* DOE Abort */
+#define  PCI_DOE_CTRL_INT_EN                   0x00000002  /* DOE Interrupt Enable */
+#define  PCI_DOE_CTRL_GO                       0x80000000  /* DOE Go */
+#define PCI_DOE_STATUS         0x0c    /* DOE Status Register */
+#define  PCI_DOE_STATUS_BUSY                   0x00000001  /* DOE Busy */
+#define  PCI_DOE_STATUS_INT_STATUS             0x00000002  /* DOE Interrupt Status */
+#define  PCI_DOE_STATUS_ERROR                  0x00000004  /* DOE Error */
+#define  PCI_DOE_STATUS_DATA_OBJECT_READY      0x80000000  /* Data Object Ready */
+#define PCI_DOE_WRITE          0x10    /* DOE Write Data Mailbox Register */
+#define PCI_DOE_READ           0x14    /* DOE Read Data Mailbox Register */
+
+/* DOE Data Object - note not actually registers */
+#define PCI_DOE_DATA_OBJECT_HEADER_1_VID       0x0000ffff
+#define PCI_DOE_DATA_OBJECT_HEADER_1_TYPE      0x00ff0000
+#define PCI_DOE_DATA_OBJECT_HEADER_2_LENGTH    0x0003ffff
+
+#define PCI_DOE_DATA_OBJECT_DISC_REQ_3_INDEX   0x000000ff
+#define PCI_DOE_DATA_OBJECT_DISC_RSP_3_VID     0x0000ffff
+#define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL        0x00ff0000
+#define PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX 0xff000000
+
 #endif /* LINUX_PCI_REGS_H */
-- 
2.28.0.rc0.12.gb6a658bd00c9