meta-phosphor/common/recipes-kernel/linux/linux-obmc/linux-dev-4.10-drivers-fsi-Add-FSI-SBEFIFO-driver.patch

From patchwork Thu May 11 02:52:53 2017
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Subject: [linux,dev-4.10] drivers: fsi: Add FSI SBEFIFO driver
From: eajames@linux.vnet.ibm.com
X-Patchwork-Id: 760920
Message-Id: <1494471173-6077-1-git-send-email-eajames@linux.vnet.ibm.com>
To: openbmc@lists.ozlabs.org
Cc: "Edward A. James" <eajames@us.ibm.com>, bradleyb@fuzziesquirrel.com
Date: Wed, 10 May 2017 21:52:53 -0500

From: "Edward A. James" <eajames@us.ibm.com>

IBM POWER9 processors contain some embedded hardware and software bits
collectively referred to as the self boot engine (SBE).  One role of
the SBE is to act as a proxy that provides access to the registers of
the POWER chip from other (embedded) systems.

The POWER9 chip contains a hardware frontend for communicating with
the SBE from remote systems called the SBEFIFO.  The SBEFIFO logic
is contained within an FSI CFAM (see Documentation/fsi) and as such
the driver implements an FSI bus device.

The SBE expects to communicate using a defined wire protocol; however,
the driver knows nothing of the protocol and only provides raw access
to the fifo device to userspace applications wishing to communicate with
the SBE using the wire protocol.

The SBEFIFO consists of two hardware fifos.  The upstream fifo is used
by the driver to transfer data to the SBE on the POWER chip, from the
system hosting the driver.  The downstream fifo is used by the driver to
transfer data from the SBE on the power chip to the system hosting the
driver.

Signed-off-by: Edward A. James <eajames@us.ibm.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
---
 drivers/fsi/Kconfig       |   5 +
 drivers/fsi/Makefile      |   1 +
 drivers/fsi/fsi-sbefifo.c | 824 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 830 insertions(+)
 create mode 100644 drivers/fsi/fsi-sbefifo.c

diff --git a/drivers/fsi/Kconfig b/drivers/fsi/Kconfig
index fc031ac..39527fa 100644
--- a/drivers/fsi/Kconfig
+++ b/drivers/fsi/Kconfig
@@ -31,6 +31,11 @@ config FSI_SCOM
 	---help---
 	This option enables an FSI based SCOM device driver.
 
+config FSI_SBEFIFO
+	tristate "SBEFIFO FSI client device driver"
+	---help---
+	This option enables an FSI based SBEFIFO device driver.
+
 endif
 
 endmenu
diff --git a/drivers/fsi/Makefile b/drivers/fsi/Makefile
index 65eb99d..851182e 100644
--- a/drivers/fsi/Makefile
+++ b/drivers/fsi/Makefile
@@ -3,3 +3,4 @@ obj-$(CONFIG_FSI) += fsi-core.o
 obj-$(CONFIG_FSI_MASTER_HUB) += fsi-master-hub.o
 obj-$(CONFIG_FSI_MASTER_GPIO) += fsi-master-gpio.o
 obj-$(CONFIG_FSI_SCOM) += fsi-scom.o
+obj-$(CONFIG_FSI_SBEFIFO) += fsi-sbefifo.o
diff --git a/drivers/fsi/fsi-sbefifo.c b/drivers/fsi/fsi-sbefifo.c
new file mode 100644
index 0000000..b49aec2
--- /dev/null
+++ b/drivers/fsi/fsi-sbefifo.c
@@ -0,0 +1,824 @@
+/*
+ * Copyright (C) IBM Corporation 2017
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERGCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/idr.h>
+#include <linux/fsi.h>
+#include <linux/list.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/timer.h>
+#include <linux/uaccess.h>
+
+/*
+ * The SBEFIFO is a pipe-like FSI device for communicating with
+ * the self boot engine on POWER processors.
+ */
+
+#define DEVICE_NAME		"sbefifo"
+#define FSI_ENGID_SBE		0x22
+#define SBEFIFO_BUF_CNT		32
+
+#define SBEFIFO_UP		0x00	/* Up register offset */
+#define SBEFIFO_DWN		0x40	/* Down register offset */
+
+#define SBEFIFO_STS		0x04
+#define   SBEFIFO_EMPTY			BIT(20)
+#define SBEFIFO_EOT_RAISE	0x08
+#define   SBEFIFO_EOT_MAGIC		0xffffffff
+#define SBEFIFO_EOT_ACK		0x14
+
+struct sbefifo {
+	struct timer_list poll_timer;
+	struct fsi_device *fsi_dev;
+	struct miscdevice mdev;
+	wait_queue_head_t wait;
+	struct list_head link;
+	struct list_head xfrs;
+	struct kref kref;
+	spinlock_t lock;
+	char name[32];
+	int idx;
+	int rc;
+};
+
+struct sbefifo_buf {
+	u32 buf[SBEFIFO_BUF_CNT];
+	unsigned long flags;
+#define SBEFIFO_BUF_FULL		1
+	u32 *rpos;
+	u32 *wpos;
+};
+
+struct sbefifo_xfr {
+	struct sbefifo_buf *rbuf;
+	struct sbefifo_buf *wbuf;
+	struct list_head client;
+	struct list_head xfrs;
+	unsigned long flags;
+#define SBEFIFO_XFR_WRITE_DONE		1
+#define SBEFIFO_XFR_RESP_PENDING	2
+#define SBEFIFO_XFR_COMPLETE		3
+#define SBEFIFO_XFR_CANCEL		4
+};
+
+struct sbefifo_client {
+	struct sbefifo_buf rbuf;
+	struct sbefifo_buf wbuf;
+	struct list_head xfrs;
+	struct sbefifo *dev;
+	struct kref kref;
+};
+
+static struct list_head sbefifo_fifos;
+
+static DEFINE_IDA(sbefifo_ida);
+
+static int sbefifo_inw(struct sbefifo *sbefifo, int reg, u32 *word)
+{
+	int rc;
+	u32 raw_word;
+
+	rc = fsi_device_read(sbefifo->fsi_dev, reg, &raw_word,
+			     sizeof(raw_word));
+	if (rc)
+		return rc;
+
+	*word = be32_to_cpu(raw_word);
+	return 0;
+}
+
+static int sbefifo_outw(struct sbefifo *sbefifo, int reg, u32 word)
+{
+	u32 raw_word = cpu_to_be32(word);
+
+	return fsi_device_write(sbefifo->fsi_dev, reg, &raw_word,
+				sizeof(raw_word));
+}
+
+static int sbefifo_readw(struct sbefifo *sbefifo, u32 *word)
+{
+	return fsi_device_read(sbefifo->fsi_dev, SBEFIFO_DWN, word,
+			       sizeof(*word));
+}
+
+static int sbefifo_writew(struct sbefifo *sbefifo, u32 word)
+{
+	return fsi_device_write(sbefifo->fsi_dev, SBEFIFO_UP, &word,
+				sizeof(word));
+}
+
+static int sbefifo_ack_eot(struct sbefifo *sbefifo)
+{
+	u32 discard;
+	int ret;
+
+	 /* Discard the EOT word. */
+	ret = sbefifo_readw(sbefifo, &discard);
+	if (ret)
+		return ret;
+
+	return sbefifo_outw(sbefifo, SBEFIFO_DWN | SBEFIFO_EOT_ACK,
+			SBEFIFO_EOT_MAGIC);
+}
+
+static size_t sbefifo_dev_nwreadable(u32 sts)
+{
+	static const u32 FIFO_NTRY_CNT_MSK = 0x000f0000;
+	static const unsigned int FIFO_NTRY_CNT_SHIFT = 16;
+
+	return (sts & FIFO_NTRY_CNT_MSK) >> FIFO_NTRY_CNT_SHIFT;
+}
+
+static size_t sbefifo_dev_nwwriteable(u32 sts)
+{
+	static const size_t FIFO_DEPTH = 8;
+
+	return FIFO_DEPTH - sbefifo_dev_nwreadable(sts);
+}
+
+static void sbefifo_buf_init(struct sbefifo_buf *buf)
+{
+	WRITE_ONCE(buf->rpos, buf->buf);
+	WRITE_ONCE(buf->wpos, buf->buf);
+}
+
+static size_t sbefifo_buf_nbreadable(struct sbefifo_buf *buf)
+{
+	size_t n;
+	u32 *rpos = READ_ONCE(buf->rpos);
+	u32 *wpos = READ_ONCE(buf->wpos);
+
+	if (test_bit(SBEFIFO_BUF_FULL, &buf->flags))
+		n = SBEFIFO_BUF_CNT;
+	else if (rpos <= wpos)
+		n = wpos - rpos;
+	else
+		n = (buf->buf + SBEFIFO_BUF_CNT) - rpos;
+
+	return n << 2;
+}
+
+static size_t sbefifo_buf_nbwriteable(struct sbefifo_buf *buf)
+{
+	size_t n;
+	u32 *rpos = READ_ONCE(buf->rpos);
+	u32 *wpos = READ_ONCE(buf->wpos);
+
+	if (test_bit(SBEFIFO_BUF_FULL, &buf->flags))
+		n = 0;
+	else if (wpos < rpos)
+		n = rpos - wpos;
+	else
+		n = (buf->buf + SBEFIFO_BUF_CNT) - wpos;
+
+	return n << 2;
+}
+
+/*
+ * Update pointers and flags after doing a buffer read.  Return true if the
+ * buffer is now empty;
+ */
+static bool sbefifo_buf_readnb(struct sbefifo_buf *buf, size_t n)
+{
+	u32 *rpos = READ_ONCE(buf->rpos);
+	u32 *wpos = READ_ONCE(buf->wpos);
+
+	if (n)
+		clear_bit(SBEFIFO_BUF_FULL, &buf->flags);
+
+	rpos += (n >> 2);
+	if (rpos == buf->buf + SBEFIFO_BUF_CNT)
+		rpos = buf->buf;
+
+	WRITE_ONCE(buf->rpos, rpos);
+	return rpos == wpos;
+}
+
+/*
+ * Update pointers and flags after doing a buffer write.  Return true if the
+ * buffer is now full.
+ */
+static bool sbefifo_buf_wrotenb(struct sbefifo_buf *buf, size_t n)
+{
+	u32 *rpos = READ_ONCE(buf->rpos);
+	u32 *wpos = READ_ONCE(buf->wpos);
+
+	wpos += (n >> 2);
+	if (wpos == buf->buf + SBEFIFO_BUF_CNT)
+		wpos = buf->buf;
+	if (wpos == rpos)
+		set_bit(SBEFIFO_BUF_FULL, &buf->flags);
+
+	WRITE_ONCE(buf->wpos, wpos);
+	return rpos == wpos;
+}
+
+static void sbefifo_free(struct kref *kref)
+{
+	struct sbefifo *sbefifo;
+
+	sbefifo = container_of(kref, struct sbefifo, kref);
+	kfree(sbefifo);
+}
+
+static void sbefifo_get(struct sbefifo *sbefifo)
+{
+	kref_get(&sbefifo->kref);
+}
+
+static void sbefifo_put(struct sbefifo *sbefifo)
+{
+	kref_put(&sbefifo->kref, sbefifo_free);
+}
+
+static struct sbefifo_xfr *sbefifo_enq_xfr(struct sbefifo_client *client)
+{
+	struct sbefifo *sbefifo = client->dev;
+	struct sbefifo_xfr *xfr;
+
+	xfr = kzalloc(sizeof(*xfr), GFP_KERNEL);
+	if (!xfr)
+		return NULL;
+
+	xfr->rbuf = &client->rbuf;
+	xfr->wbuf = &client->wbuf;
+	list_add_tail(&xfr->xfrs, &sbefifo->xfrs);
+	list_add_tail(&xfr->client, &client->xfrs);
+
+	return xfr;
+}
+
+static struct sbefifo_xfr *sbefifo_client_next_xfr(
+		struct sbefifo_client *client)
+{
+	if (list_empty(&client->xfrs))
+		return NULL;
+
+	return container_of(client->xfrs.next, struct sbefifo_xfr,
+			client);
+}
+
+static bool sbefifo_xfr_rsp_pending(struct sbefifo_client *client)
+{
+	struct sbefifo_xfr *xfr;
+
+	xfr = sbefifo_client_next_xfr(client);
+	if (xfr && test_bit(SBEFIFO_XFR_RESP_PENDING, &xfr->flags))
+		return true;
+
+	return false;
+}
+
+static struct sbefifo_client *sbefifo_new_client(struct sbefifo *sbefifo)
+{
+	struct sbefifo_client *client;
+
+	client = kzalloc(sizeof(*client), GFP_KERNEL);
+	if (!client)
+		return NULL;
+
+	kref_init(&client->kref);
+	client->dev = sbefifo;
+	sbefifo_buf_init(&client->rbuf);
+	sbefifo_buf_init(&client->wbuf);
+	INIT_LIST_HEAD(&client->xfrs);
+
+	sbefifo_get(sbefifo);
+
+	return client;
+}
+
+static void sbefifo_client_release(struct kref *kref)
+{
+	struct sbefifo_client *client;
+	struct sbefifo_xfr *xfr;
+
+	client = container_of(kref, struct sbefifo_client, kref);
+	list_for_each_entry(xfr, &client->xfrs, client) {
+		/*
+		 * The client left with pending or running xfrs.
+		 * Cancel them.
+		 */
+		set_bit(SBEFIFO_XFR_CANCEL, &xfr->flags);
+		sbefifo_get(client->dev);
+		if (mod_timer(&client->dev->poll_timer, jiffies))
+			sbefifo_put(client->dev);
+	}
+
+	sbefifo_put(client->dev);
+	kfree(client);
+}
+
+static void sbefifo_get_client(struct sbefifo_client *client)
+{
+	kref_get(&client->kref);
+}
+
+static void sbefifo_put_client(struct sbefifo_client *client)
+{
+	kref_put(&client->kref, sbefifo_client_release);
+}
+
+static struct sbefifo_xfr *sbefifo_next_xfr(struct sbefifo *sbefifo)
+{
+	struct sbefifo_xfr *xfr, *tmp;
+
+	list_for_each_entry_safe(xfr, tmp, &sbefifo->xfrs, xfrs) {
+		if (unlikely(test_bit(SBEFIFO_XFR_CANCEL, &xfr->flags))) {
+			/* Discard cancelled transfers. */
+			list_del(&xfr->xfrs);
+			kfree(xfr);
+			continue;
+		}
+		return xfr;
+	}
+
+	return NULL;
+}
+
+static void sbefifo_poll_timer(unsigned long data)
+{
+	static const unsigned long EOT_MASK = 0x000000ff;
+	struct sbefifo *sbefifo = (void *)data;
+	struct sbefifo_buf *rbuf, *wbuf;
+	struct sbefifo_xfr *xfr = NULL;
+	struct sbefifo_buf drain;
+	size_t devn, bufn;
+	int eot = 0;
+	int ret = 0;
+	u32 sts;
+	int i;
+
+	spin_lock(&sbefifo->lock);
+	xfr = list_first_entry_or_null(&sbefifo->xfrs, struct sbefifo_xfr,
+			xfrs);
+	if (!xfr)
+		goto out_unlock;
+
+	rbuf = xfr->rbuf;
+	wbuf = xfr->wbuf;
+
+	if (unlikely(test_bit(SBEFIFO_XFR_CANCEL, &xfr->flags))) {
+		/* The client left. */
+		rbuf = &drain;
+		wbuf = &drain;
+		sbefifo_buf_init(&drain);
+		if (!test_bit(SBEFIFO_XFR_RESP_PENDING, &xfr->flags))
+			set_bit(SBEFIFO_XFR_WRITE_DONE, &xfr->flags);
+	}
+
+	 /* Drain the write buffer. */
+	while ((bufn = sbefifo_buf_nbreadable(wbuf))) {
+		ret = sbefifo_inw(sbefifo, SBEFIFO_UP | SBEFIFO_STS,
+				&sts);
+		if (ret)
+			goto out;
+
+		devn = sbefifo_dev_nwwriteable(sts);
+		if (devn == 0) {
+			/* No open slot for write.  Reschedule. */
+			sbefifo->poll_timer.expires = jiffies +
+				msecs_to_jiffies(500);
+			add_timer(&sbefifo->poll_timer);
+			goto out_unlock;
+		}
+
+		devn = min_t(size_t, devn, bufn >> 2);
+		for (i = 0; i < devn; i++) {
+			ret = sbefifo_writew(sbefifo, *wbuf->rpos);
+			if (ret)
+				goto out;
+
+			sbefifo_buf_readnb(wbuf, 1 << 2);
+		}
+	}
+
+	 /* Send EOT if the writer is finished. */
+	if (test_and_clear_bit(SBEFIFO_XFR_WRITE_DONE, &xfr->flags)) {
+		ret = sbefifo_outw(sbefifo,
+				SBEFIFO_UP | SBEFIFO_EOT_RAISE,
+				SBEFIFO_EOT_MAGIC);
+		if (ret)
+			goto out;
+
+		/* Inform reschedules that the writer is finished. */
+		set_bit(SBEFIFO_XFR_RESP_PENDING, &xfr->flags);
+	}
+
+	/* Nothing left to do if the writer is not finished. */
+	if (!test_bit(SBEFIFO_XFR_RESP_PENDING, &xfr->flags))
+		goto out;
+
+	 /* Fill the read buffer. */
+	while ((bufn = sbefifo_buf_nbwriteable(rbuf))) {
+		ret = sbefifo_inw(sbefifo, SBEFIFO_DWN | SBEFIFO_STS, &sts);
+		if (ret)
+			goto out;
+
+		devn = sbefifo_dev_nwreadable(sts);
+		if (devn == 0) {
+			/* No data yet.  Reschedule. */
+			sbefifo->poll_timer.expires = jiffies +
+				msecs_to_jiffies(500);
+			add_timer(&sbefifo->poll_timer);
+			goto out_unlock;
+		}
+
+		/* Fill.  The EOT word is discarded.  */
+		devn = min_t(size_t, devn, bufn >> 2);
+		eot = (sts & EOT_MASK) != 0;
+		if (eot)
+			devn--;
+
+		for (i = 0; i < devn; i++) {
+			ret = sbefifo_readw(sbefifo, rbuf->wpos);
+			if (ret)
+				goto out;
+
+			if (likely(!test_bit(SBEFIFO_XFR_CANCEL, &xfr->flags)))
+				sbefifo_buf_wrotenb(rbuf, 1 << 2);
+		}
+
+		if (eot) {
+			ret = sbefifo_ack_eot(sbefifo);
+			if (ret)
+				goto out;
+
+			set_bit(SBEFIFO_XFR_COMPLETE, &xfr->flags);
+			list_del(&xfr->xfrs);
+			if (unlikely(test_bit(SBEFIFO_XFR_CANCEL,
+							&xfr->flags)))
+				kfree(xfr);
+			break;
+		}
+	}
+
+out:
+	if (unlikely(ret)) {
+		sbefifo->rc = ret;
+		dev_err(&sbefifo->fsi_dev->dev,
+				"Fatal bus access failure: %d\n", ret);
+		list_for_each_entry(xfr, &sbefifo->xfrs, xfrs)
+			kfree(xfr);
+		INIT_LIST_HEAD(&sbefifo->xfrs);
+
+	} else if (eot && sbefifo_next_xfr(sbefifo)) {
+		sbefifo_get(sbefifo);
+		sbefifo->poll_timer.expires = jiffies;
+		add_timer(&sbefifo->poll_timer);
+	}
+
+	sbefifo_put(sbefifo);
+	wake_up(&sbefifo->wait);
+
+out_unlock:
+	spin_unlock(&sbefifo->lock);
+}
+
+static int sbefifo_open(struct inode *inode, struct file *file)
+{
+	struct sbefifo *sbefifo = container_of(file->private_data,
+			struct sbefifo, mdev);
+	struct sbefifo_client *client;
+	int ret;
+
+	ret = READ_ONCE(sbefifo->rc);
+	if (ret)
+		return ret;
+
+	client = sbefifo_new_client(sbefifo);
+	if (!client)
+		return -ENOMEM;
+
+	file->private_data = client;
+
+	return 0;
+}
+
+static unsigned int sbefifo_poll(struct file *file, poll_table *wait)
+{
+	struct sbefifo_client *client = file->private_data;
+	struct sbefifo *sbefifo = client->dev;
+	unsigned int mask = 0;
+
+	poll_wait(file, &sbefifo->wait, wait);
+
+	if (READ_ONCE(sbefifo->rc))
+		mask |= POLLERR;
+
+	if (sbefifo_buf_nbreadable(&client->rbuf))
+		mask |= POLLIN;
+
+	if (sbefifo_buf_nbwriteable(&client->wbuf))
+		mask |= POLLOUT;
+
+	return mask;
+}
+
+static ssize_t sbefifo_read(struct file *file, char __user *buf,
+		size_t len, loff_t *offset)
+{
+	struct sbefifo_client *client = file->private_data;
+	struct sbefifo *sbefifo = client->dev;
+	struct sbefifo_xfr *xfr;
+	ssize_t ret = 0;
+	size_t n;
+
+	WARN_ON(*offset);
+
+	if (!access_ok(VERIFY_WRITE, buf, len))
+		return -EFAULT;
+
+	if ((len >> 2) << 2 != len)
+		return -EINVAL;
+
+	if ((file->f_flags & O_NONBLOCK) && !sbefifo_xfr_rsp_pending(client))
+		return -EAGAIN;
+
+	sbefifo_get_client(client);
+	if (wait_event_interruptible(sbefifo->wait,
+				(ret = READ_ONCE(sbefifo->rc)) ||
+				(n = sbefifo_buf_nbreadable(
+						&client->rbuf)))) {
+		sbefifo_put_client(client);
+		return -ERESTARTSYS;
+	}
+	if (ret) {
+		INIT_LIST_HEAD(&client->xfrs);
+		sbefifo_put_client(client);
+		return ret;
+	}
+
+	n = min_t(size_t, n, len);
+
+	if (copy_to_user(buf, READ_ONCE(client->rbuf.rpos), n)) {
+		sbefifo_put_client(client);
+		return -EFAULT;
+	}
+
+	if (sbefifo_buf_readnb(&client->rbuf, n)) {
+		xfr = sbefifo_client_next_xfr(client);
+		if (!test_bit(SBEFIFO_XFR_COMPLETE, &xfr->flags)) {
+			/*
+			 * Fill the read buffer back up.
+			 */
+			sbefifo_get(sbefifo);
+			if (mod_timer(&client->dev->poll_timer, jiffies))
+				sbefifo_put(sbefifo);
+		} else {
+			kfree(xfr);
+			list_del(&xfr->client);
+			wake_up(&sbefifo->wait);
+		}
+	}
+
+	sbefifo_put_client(client);
+
+	return n;
+}
+
+static ssize_t sbefifo_write(struct file *file, const char __user *buf,
+		size_t len, loff_t *offset)
+{
+	struct sbefifo_client *client = file->private_data;
+	struct sbefifo *sbefifo = client->dev;
+	struct sbefifo_xfr *xfr;
+	ssize_t ret = 0;
+	size_t n;
+
+	WARN_ON(*offset);
+
+	if (!access_ok(VERIFY_READ, buf, len))
+		return -EFAULT;
+
+	if ((len >> 2) << 2 != len)
+		return -EINVAL;
+
+	if (!len)
+		return 0;
+
+	n = sbefifo_buf_nbwriteable(&client->wbuf);
+
+	spin_lock_irq(&sbefifo->lock);
+	xfr = sbefifo_next_xfr(sbefifo);
+
+	if ((file->f_flags & O_NONBLOCK) && xfr && n < len) {
+		spin_unlock_irq(&sbefifo->lock);
+		return -EAGAIN;
+	}
+
+	xfr = sbefifo_enq_xfr(client);
+	if (!xfr) {
+		spin_unlock_irq(&sbefifo->lock);
+		return -ENOMEM;
+	}
+	spin_unlock_irq(&sbefifo->lock);
+
+	sbefifo_get_client(client);
+
+	/*
+	 * Partial writes are not really allowed in that EOT is sent exactly
+	 * once per write.
+	 */
+	while (len) {
+		if (wait_event_interruptible(sbefifo->wait,
+				READ_ONCE(sbefifo->rc) ||
+					(sbefifo_client_next_xfr(client) == xfr &&
+					 (n = sbefifo_buf_nbwriteable(
+							&client->wbuf))))) {
+			set_bit(SBEFIFO_XFR_CANCEL, &xfr->flags);
+			sbefifo_get(sbefifo);
+			if (mod_timer(&sbefifo->poll_timer, jiffies))
+				sbefifo_put(sbefifo);
+
+			sbefifo_put_client(client);
+			return -ERESTARTSYS;
+		}
+		if (sbefifo->rc) {
+			INIT_LIST_HEAD(&client->xfrs);
+			sbefifo_put_client(client);
+			return sbefifo->rc;
+		}
+
+		n = min_t(size_t, n, len);
+
+		if (copy_from_user(READ_ONCE(client->wbuf.wpos), buf, n)) {
+			set_bit(SBEFIFO_XFR_CANCEL, &xfr->flags);
+			sbefifo_get(sbefifo);
+			if (mod_timer(&sbefifo->poll_timer, jiffies))
+				sbefifo_put(sbefifo);
+			sbefifo_put_client(client);
+			return -EFAULT;
+		}
+
+		sbefifo_buf_wrotenb(&client->wbuf, n);
+		len -= n;
+		buf += n;
+		ret += n;
+
+		/*
+		 * Drain the write buffer.
+		 */
+		sbefifo_get(sbefifo);
+		if (mod_timer(&client->dev->poll_timer, jiffies))
+			sbefifo_put(sbefifo);
+	}
+
+	set_bit(SBEFIFO_XFR_WRITE_DONE, &xfr->flags);
+	sbefifo_put_client(client);
+
+	return ret;
+}
+
+static int sbefifo_release(struct inode *inode, struct file *file)
+{
+	struct sbefifo_client *client = file->private_data;
+	struct sbefifo *sbefifo = client->dev;
+
+	sbefifo_put_client(client);
+
+	return READ_ONCE(sbefifo->rc);
+}
+
+static const struct file_operations sbefifo_fops = {
+	.owner		= THIS_MODULE,
+	.open		= sbefifo_open,
+	.read		= sbefifo_read,
+	.write		= sbefifo_write,
+	.poll		= sbefifo_poll,
+	.release	= sbefifo_release,
+};
+
+static int sbefifo_probe(struct device *dev)
+{
+	struct fsi_device *fsi_dev = to_fsi_dev(dev);
+	struct sbefifo *sbefifo;
+	u32 sts;
+	int ret;
+
+	dev_info(dev, "Found sbefifo device\n");
+	sbefifo = kzalloc(sizeof(*sbefifo), GFP_KERNEL);
+	if (!sbefifo)
+		return -ENOMEM;
+
+	sbefifo->fsi_dev = fsi_dev;
+
+	ret = sbefifo_inw(sbefifo,
+			SBEFIFO_UP | SBEFIFO_STS, &sts);
+	if (ret)
+		return ret;
+	if (!(sts & SBEFIFO_EMPTY)) {
+		dev_err(&sbefifo->fsi_dev->dev,
+				"Found data in upstream fifo\n");
+		return -EIO;
+	}
+
+	ret = sbefifo_inw(sbefifo, SBEFIFO_DWN | SBEFIFO_STS, &sts);
+	if (ret)
+		return ret;
+	if (!(sts & SBEFIFO_EMPTY)) {
+		dev_err(&sbefifo->fsi_dev->dev,
+				"Found data in downstream fifo\n");
+		return -EIO;
+	}
+
+	sbefifo->mdev.minor = MISC_DYNAMIC_MINOR;
+	sbefifo->mdev.fops = &sbefifo_fops;
+	sbefifo->mdev.name = sbefifo->name;
+	sbefifo->mdev.parent = dev;
+	spin_lock_init(&sbefifo->lock);
+	kref_init(&sbefifo->kref);
+
+	sbefifo->idx = ida_simple_get(&sbefifo_ida, 1, INT_MAX, GFP_KERNEL);
+	snprintf(sbefifo->name, sizeof(sbefifo->name), "sbefifo%d",
+			sbefifo->idx);
+	init_waitqueue_head(&sbefifo->wait);
+	INIT_LIST_HEAD(&sbefifo->xfrs);
+
+	/* This bit of silicon doesn't offer any interrupts... */
+	setup_timer(&sbefifo->poll_timer, sbefifo_poll_timer,
+			(unsigned long)sbefifo);
+
+	list_add(&sbefifo->link, &sbefifo_fifos);
+	return misc_register(&sbefifo->mdev);
+}
+
+static int sbefifo_remove(struct device *dev)
+{
+	struct fsi_device *fsi_dev = to_fsi_dev(dev);
+	struct sbefifo *sbefifo, *sbefifo_tmp;
+	struct sbefifo_xfr *xfr;
+
+	list_for_each_entry_safe(sbefifo, sbefifo_tmp, &sbefifo_fifos, link) {
+		if (sbefifo->fsi_dev != fsi_dev)
+			continue;
+		misc_deregister(&sbefifo->mdev);
+		list_del(&sbefifo->link);
+		ida_simple_remove(&sbefifo_ida, sbefifo->idx);
+
+		if (del_timer_sync(&sbefifo->poll_timer))
+			sbefifo_put(sbefifo);
+
+		spin_lock(&sbefifo->lock);
+		list_for_each_entry(xfr, &sbefifo->xfrs, xfrs)
+			kfree(xfr);
+		spin_unlock(&sbefifo->lock);
+
+		WRITE_ONCE(sbefifo->rc, -ENODEV);
+
+		wake_up(&sbefifo->wait);
+		sbefifo_put(sbefifo);
+	}
+
+	return 0;
+}
+
+static struct fsi_device_id sbefifo_ids[] = {
+	{
+		.engine_type = FSI_ENGID_SBE,
+		.version = FSI_VERSION_ANY,
+	},
+	{ 0 }
+};
+
+static struct fsi_driver sbefifo_drv = {
+	.id_table = sbefifo_ids,
+	.drv = {
+		.name = DEVICE_NAME,
+		.bus = &fsi_bus_type,
+		.probe = sbefifo_probe,
+		.remove = sbefifo_remove,
+	}
+};
+
+static int sbefifo_init(void)
+{
+	INIT_LIST_HEAD(&sbefifo_fifos);
+	return fsi_driver_register(&sbefifo_drv);
+}
+
+static void sbefifo_exit(void)
+{
+	fsi_driver_unregister(&sbefifo_drv);
+}
+
+module_init(sbefifo_init);
+module_exit(sbefifo_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Brad Bishop <bradleyb@fuzziesquirrel.com>");
+MODULE_DESCRIPTION("Linux device interface to the POWER self boot engine");