Message-Id: <20190627125152.54905-6-alexander.shishkin@linux.intel.com>
Date:   Thu, 27 Jun 2019 15:51:48 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [GIT PULL 5/9] intel_th: msu: Introduce buffer driver interface

Introduces a concept of buffer drivers, which is a mechanism for creating
trace sinks that would receive trace data from MSC buffers and transfer it
elsewhere.

A buffer driver can implement its own window allocation/deallocation if
it has to. It must provide a callback that's used to notify it when a
window fills up, so that it can then start a DMA transaction from that
window 'elsewhere'. This window remains in a 'locked' state and won't be
used for storing new trace data until the buffer driver 'unlocks' it with
a provided API call, at which point the window can be used again for
storing trace data.

This relies on a functional "last block" interrupt, so not all versions of
Trace Hub can use this feature.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 .../testing/sysfs-bus-intel_th-devices-msc    |   3 +-
 MAINTAINERS                                   |   1 +
 drivers/hwtracing/intel_th/msu.c              | 355 +++++++++++++++++-
 drivers/hwtracing/intel_th/msu.h              |  23 +-
 include/linux/intel_th.h                      |  67 ++++
 5 files changed, 419 insertions(+), 30 deletions(-)
 create mode 100644 include/linux/intel_th.h

diff --git a/Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc b/Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc
index f54ae244f3f1..7da00601afdc 100644
--- a/Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc
+++ b/Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc
@@ -12,7 +12,8 @@ Description:	(RW) Configure MSC operating mode:
 		  - "single", for contiguous buffer mode (high-order alloc);
 		  - "multi", for multiblock mode;
 		  - "ExI", for DCI handler mode;
-		  - "debug", for debug mode.
+		  - "debug", for debug mode;
+		  - any of the currently loaded buffer drivers.
 		If operating mode changes, existing buffer is deallocated,
 		provided there are no active users and tracing is not enabled,
 		otherwise the write will fail.
diff --git a/MAINTAINERS b/MAINTAINERS
index 5cfbea4ce575..9fba97fbac64 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8152,6 +8152,7 @@ M:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
 S:	Supported
 F:	Documentation/trace/intel_th.rst
 F:	drivers/hwtracing/intel_th/
+F:	include/linux/intel_th.h
 
 INTEL(R) TRUSTED EXECUTION TECHNOLOGY (TXT)
 M:	Ning Sun <ning.sun@...el.com>
diff --git a/drivers/hwtracing/intel_th/msu.c b/drivers/hwtracing/intel_th/msu.c
index 59a596911e54..fc9890e56e5b 100644
--- a/drivers/hwtracing/intel_th/msu.c
+++ b/drivers/hwtracing/intel_th/msu.c
@@ -17,12 +17,14 @@
 #include <linux/mm.h>
 #include <linux/fs.h>
 #include <linux/io.h>
+#include <linux/workqueue.h>
 #include <linux/dma-mapping.h>
 
 #ifdef CONFIG_X86
 #include <asm/set_memory.h>
 #endif
 
+#include <linux/intel_th.h>
 #include "intel_th.h"
 #include "msu.h"
 
@@ -32,6 +34,7 @@
  * struct msc_window - multiblock mode window descriptor
  * @entry:	window list linkage (msc::win_list)
  * @pgoff:	page offset into the buffer that this window starts at
+ * @lockout:	lockout state, see comment below
  * @nr_blocks:	number of blocks (pages) in this window
  * @nr_segs:	number of segments in this window (<= @nr_blocks)
  * @_sgt:	array of block descriptors
@@ -40,6 +43,7 @@
 struct msc_window {
 	struct list_head	entry;
 	unsigned long		pgoff;
+	atomic_t		lockout;
 	unsigned int		nr_blocks;
 	unsigned int		nr_segs;
 	struct msc		*msc;
@@ -100,6 +104,10 @@ struct msc {
 	void __iomem		*msu_base;
 	struct intel_th_device	*thdev;
 
+	const struct msu_buffer_driver	*bdrv;
+	void				*bdrv_priv;
+
+	struct work_struct	work;
 	struct list_head	win_list;
 	struct sg_table		single_sgt;
 	struct msc_window	*cur_win;
@@ -126,6 +134,110 @@ struct msc {
 	unsigned int		index;
 };
 
+/*
+ * Lockout state transitions:
+ *   READY -> INUSE -+-> LOCKED -+-> READY -> etc.
+ *                   \-----------/
+ * WIN_READY:	window can be used by HW
+ * WIN_INUSE:	window is in use
+ * WIN_LOCKED:	window is filled up and is being processed by the buffer driver
+ *
+ * All state transitions happen automatically, except for the LOCKED->READY,
+ * which needs to be signalled by the buffer driver by calling
+ * intel_th_msc_window_unlock().
+ *
+ * When the interrupt handler has to switch to the next window, it checks
+ * whether it's READY, and if it is, it performs the switch and tracing
+ * continues. If it's LOCKED, it stops the trace.
+ */
+enum {
+	WIN_READY = 0,
+	WIN_INUSE,
+	WIN_LOCKED
+};
+
+static LIST_HEAD(msu_buffer_list);
+static struct mutex msu_buffer_mutex;
+
+struct msu_buffer {
+	struct list_head		entry;
+	const struct msu_buffer_driver	*bdrv;
+};
+
+static struct msu_buffer *__msu_buffer_find(const char *name)
+{
+	struct msu_buffer *buf;
+
+	list_for_each_entry(buf, &msu_buffer_list, entry) {
+		if (!strcmp(buf->bdrv->name, name))
+			return buf;
+	}
+
+	return NULL;
+}
+
+static const struct msu_buffer_driver *
+__msu_buffer_driver_find(const char *name)
+{
+	struct msu_buffer *buf = __msu_buffer_find(name);
+
+	return buf ? buf->bdrv : NULL;
+}
+
+static const struct msu_buffer_driver *
+msu_buffer_driver_get(const char *name)
+{
+	const struct msu_buffer_driver *bdrv;
+
+	mutex_lock(&msu_buffer_mutex);
+	bdrv = __msu_buffer_driver_find(name);
+	if (bdrv && !try_module_get(bdrv->owner))
+		bdrv = NULL;
+	mutex_unlock(&msu_buffer_mutex);
+
+	return bdrv;
+}
+
+int intel_th_msu_buffer_register(const struct msu_buffer_driver *bdrv)
+{
+	struct msu_buffer *buf;
+	int ret = -EEXIST;
+
+	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	mutex_lock(&msu_buffer_mutex);
+	if (__msu_buffer_driver_find(bdrv->name))
+		goto out;
+
+	buf->bdrv = bdrv;
+	list_add_tail(&buf->entry, &msu_buffer_list);
+	ret = 0;
+out:
+	mutex_unlock(&msu_buffer_mutex);
+
+	if (ret)
+		kfree(buf);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(intel_th_msu_buffer_register);
+
+void intel_th_msu_buffer_unregister(const struct msu_buffer_driver *bdrv)
+{
+	struct msu_buffer *buf;
+
+	mutex_lock(&msu_buffer_mutex);
+	buf = __msu_buffer_find(bdrv->name);
+	if (buf) {
+		list_del(&buf->entry);
+		kfree(buf);
+	}
+	mutex_unlock(&msu_buffer_mutex);
+}
+EXPORT_SYMBOL_GPL(intel_th_msu_buffer_unregister);
+
 static inline bool msc_block_is_empty(struct msc_block_desc *bdesc)
 {
 	/* header hasn't been written */
@@ -188,6 +300,25 @@ static struct msc_window *msc_next_window(struct msc_window *win)
 	return list_next_entry(win, entry);
 }
 
+static size_t msc_win_total_sz(struct msc_window *win)
+{
+	unsigned int blk;
+	size_t size = 0;
+
+	for (blk = 0; blk < win->nr_segs; blk++) {
+		struct msc_block_desc *bdesc = msc_win_block(win, blk);
+
+		if (msc_block_wrapped(bdesc))
+			return win->nr_blocks << PAGE_SHIFT;
+
+		size += msc_total_sz(bdesc);
+		if (msc_block_last_written(bdesc))
+			break;
+	}
+
+	return size;
+}
+
 /**
  * msc_find_window() - find a window matching a given sg_table
  * @msc:	MSC device
@@ -527,6 +658,9 @@ static int intel_th_msu_init(struct msc *msc)
 	if (!msc->do_irq)
 		return 0;
 
+	if (!msc->bdrv)
+		return 0;
+
 	mintctl = ioread32(msc->msu_base + REG_MSU_MINTCTL);
 	mintctl |= msc->index ? M1BLIE : M0BLIE;
 	iowrite32(mintctl, msc->msu_base + REG_MSU_MINTCTL);
@@ -554,6 +688,27 @@ static void intel_th_msu_deinit(struct msc *msc)
 	iowrite32(mintctl, msc->msu_base + REG_MSU_MINTCTL);
 }
 
+static int msc_win_set_lockout(struct msc_window *win, int expect, int new)
+{
+	int old;
+
+	if (!win->msc->bdrv)
+		return 0;
+
+	old = atomic_cmpxchg(&win->lockout, expect, new);
+	if (expect == WIN_READY && old == WIN_LOCKED)
+		return -EBUSY;
+
+	/* from intel_th_msc_window_unlock(), don't warn if not locked */
+	if (expect == WIN_LOCKED && old == new)
+		return 0;
+
+	if (WARN_ONCE(old != expect, "expected lockout state %d, got %d\n",
+		      expect, old))
+		return -EINVAL;
+
+	return 0;
+}
 /**
  * msc_configure() - set up MSC hardware
  * @msc:	the MSC device to configure
@@ -571,8 +726,16 @@ static int msc_configure(struct msc *msc)
 	if (msc->mode > MSC_MODE_MULTI)
 		return -ENOTSUPP;
 
-	if (msc->mode == MSC_MODE_MULTI)
+	if (msc->mode == MSC_MODE_MULTI) {
+		/* Window allocation path makes sure this doesn't happen */
+		if (WARN_ON_ONCE(!msc->cur_win))
+			return -EINVAL;
+
+		if (msc_win_set_lockout(msc->cur_win, WIN_READY, WIN_INUSE))
+			return -EBUSY;
+
 		msc_buffer_clear_hw_header(msc);
+	}
 
 	reg = msc->base_addr >> PAGE_SHIFT;
 	iowrite32(reg, msc->reg_base + REG_MSU_MSC0BAR);
@@ -594,10 +757,14 @@ static int msc_configure(struct msc *msc)
 
 	iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);
 
+	intel_th_msu_init(msc);
+
 	msc->thdev->output.multiblock = msc->mode == MSC_MODE_MULTI;
 	intel_th_trace_enable(msc->thdev);
 	msc->enabled = 1;
 
+	if (msc->bdrv && msc->bdrv->activate)
+		msc->bdrv->activate(msc->bdrv_priv);
 
 	return 0;
 }
@@ -611,10 +778,17 @@ static int msc_configure(struct msc *msc)
  */
 static void msc_disable(struct msc *msc)
 {
+	struct msc_window *win = msc->cur_win;
 	u32 reg;
 
 	lockdep_assert_held(&msc->buf_mutex);
 
+	if (msc->mode == MSC_MODE_MULTI)
+		msc_win_set_lockout(win, WIN_INUSE, WIN_LOCKED);
+
+	if (msc->bdrv && msc->bdrv->deactivate)
+		msc->bdrv->deactivate(msc->bdrv_priv);
+	intel_th_msu_deinit(msc);
 	intel_th_trace_disable(msc->thdev);
 
 	if (msc->mode == MSC_MODE_SINGLE) {
@@ -630,6 +804,11 @@ static void msc_disable(struct msc *msc)
 	reg = ioread32(msc->reg_base + REG_MSU_MSC0CTL);
 	reg &= ~MSC_EN;
 	iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);
+
+	if (msc->bdrv && msc->bdrv->ready)
+		msc->bdrv->ready(msc->bdrv_priv, win->sgt,
+				 msc_win_total_sz(win));
+
 	msc->enabled = 0;
 
 	iowrite32(0, msc->reg_base + REG_MSU_MSC0BAR);
@@ -640,6 +819,10 @@ static void msc_disable(struct msc *msc)
 
 	reg = ioread32(msc->reg_base + REG_MSU_MSC0STS);
 	dev_dbg(msc_dev(msc), "MSCnSTS: %08x\n", reg);
+
+	reg = ioread32(msc->reg_base + REG_MSU_MSUSTS);
+	reg &= msc->index ? MSUSTS_MSC1BLAST : MSUSTS_MSC0BLAST;
+	iowrite32(reg, msc->reg_base + REG_MSU_MSUSTS);
 }
 
 static int intel_th_msc_activate(struct intel_th_device *thdev)
@@ -865,14 +1048,20 @@ static int msc_buffer_win_alloc(struct msc *msc, unsigned int nr_blocks)
 		win->pgoff = prev->pgoff + prev->nr_blocks;
 	}
 
-	ret = __msc_buffer_win_alloc(win, nr_blocks);
-	if (ret < 0)
+	if (msc->bdrv && msc->bdrv->alloc_window)
+		ret = msc->bdrv->alloc_window(msc->bdrv_priv, &win->sgt,
+					      nr_blocks << PAGE_SHIFT);
+	else
+		ret = __msc_buffer_win_alloc(win, nr_blocks);
+
+	if (ret <= 0)
 		goto err_nomem;
 
 	msc_buffer_set_uc(win, ret);
 
 	win->nr_segs = ret;
 	win->nr_blocks = nr_blocks;
+	atomic_set(&win->lockout, WIN_READY);
 
 	if (list_empty(&msc->win_list)) {
 		msc->base = msc_win_block(win, 0);
@@ -925,7 +1114,10 @@ static void msc_buffer_win_free(struct msc *msc, struct msc_window *win)
 
 	msc_buffer_set_wb(win);
 
-	__msc_buffer_win_free(msc, win);
+	if (msc->bdrv && msc->bdrv->free_window)
+		msc->bdrv->free_window(msc->bdrv_priv, win->sgt);
+	else
+		__msc_buffer_win_free(msc, win);
 
 	kfree(win);
 }
@@ -1463,18 +1655,76 @@ static void msc_win_switch(struct msc *msc)
 	intel_th_trace_switch(msc->thdev);
 }
 
+/*
+ * @dev:	MSC device to which this relates
+ * @sgt:	buffer driver's sg_table for the window, can't be NULL
+ */
+void intel_th_msc_window_unlock(struct device *dev, struct sg_table *sgt)
+{
+	struct msc *msc = dev_get_drvdata(dev);
+	struct msc_window *win;
+
+	if (WARN_ON_ONCE(!sgt))
+		return;
+
+	win = msc_find_window(msc, sgt, false);
+	if (!win)
+		return;
+
+	msc_win_set_lockout(win, WIN_LOCKED, WIN_READY);
+}
+EXPORT_SYMBOL_GPL(intel_th_msc_window_unlock);
+
+static void msc_work(struct work_struct *work)
+{
+	struct msc *msc = container_of(work, struct msc, work);
+
+	intel_th_msc_deactivate(msc->thdev);
+}
+
 static irqreturn_t intel_th_msc_interrupt(struct intel_th_device *thdev)
 {
 	struct msc *msc = dev_get_drvdata(&thdev->dev);
 	u32 msusts = ioread32(msc->msu_base + REG_MSU_MSUSTS);
 	u32 mask = msc->index ? MSUSTS_MSC1BLAST : MSUSTS_MSC0BLAST;
+	struct msc_window *win, *next_win;
 
-	if (!(msusts & mask)) {
-		if (msc->enabled)
-			return IRQ_HANDLED;
+	if (!msc->do_irq || !msc->bdrv)
 		return IRQ_NONE;
+
+	msusts &= mask;
+
+	if (!msusts)
+		return msc->enabled ? IRQ_HANDLED : IRQ_NONE;
+
+	iowrite32(msusts, msc->msu_base + REG_MSU_MSUSTS);
+
+	if (!msc->enabled)
+		return IRQ_NONE;
+
+	/* grab the window before we do the switch */
+	win = msc->cur_win;
+	if (WARN_ON_ONCE(!win))
+		return IRQ_HANDLED;
+	next_win = msc_next_window(win);
+	if (WARN_ON_ONCE(!next_win))
+		return IRQ_HANDLED;
+
+	/* next window: if READY, proceed, if LOCKED, stop the trace */
+	if (msc_win_set_lockout(next_win, WIN_READY, WIN_INUSE)) {
+		schedule_work(&msc->work);
+		return IRQ_HANDLED;
 	}
 
+	/* current window: INUSE -> LOCKED */
+	msc_win_set_lockout(win, WIN_INUSE, WIN_LOCKED);
+
+	msc_win_switch(msc);
+
+	if (msc->bdrv && msc->bdrv->ready)
+		msc->bdrv->ready(msc->bdrv_priv, win->sgt,
+				 msc_win_total_sz(win));
+
 	return IRQ_HANDLED;
 }
 
@@ -1512,21 +1762,43 @@ wrap_store(struct device *dev, struct device_attribute *attr, const char *buf,
 
 static DEVICE_ATTR_RW(wrap);
 
+static void msc_buffer_unassign(struct msc *msc)
+{
+	lockdep_assert_held(&msc->buf_mutex);
+
+	if (!msc->bdrv)
+		return;
+
+	msc->bdrv->unassign(msc->bdrv_priv);
+	module_put(msc->bdrv->owner);
+	msc->bdrv_priv = NULL;
+	msc->bdrv = NULL;
+}
+
 static ssize_t
 mode_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	struct msc *msc = dev_get_drvdata(dev);
+	const char *mode = msc_mode[msc->mode];
+	ssize_t ret;
 
-	return scnprintf(buf, PAGE_SIZE, "%s\n", msc_mode[msc->mode]);
+	mutex_lock(&msc->buf_mutex);
+	if (msc->bdrv)
+		mode = msc->bdrv->name;
+	ret = scnprintf(buf, PAGE_SIZE, "%s\n", mode);
+	mutex_unlock(&msc->buf_mutex);
+
+	return ret;
 }
 
 static ssize_t
 mode_store(struct device *dev, struct device_attribute *attr, const char *buf,
 	   size_t size)
 {
+	const struct msu_buffer_driver *bdrv = NULL;
 	struct msc *msc = dev_get_drvdata(dev);
 	size_t len = size;
-	char *cp;
+	char *cp, *mode;
 	int i, ret;
 
 	if (!capable(CAP_SYS_RAWIO))
@@ -1536,17 +1808,59 @@ mode_store(struct device *dev, struct device_attribute *attr, const char *buf,
 	if (cp)
 		len = cp - buf;
 
-	for (i = 0; i < ARRAY_SIZE(msc_mode); i++)
-		if (!strncmp(msc_mode[i], buf, len))
-			goto found;
+	mode = kstrndup(buf, len, GFP_KERNEL);
+	i = match_string(msc_mode, ARRAY_SIZE(msc_mode), mode);
+	if (i >= 0)
+		goto found;
+
+	/* Buffer drivers only work with a usable IRQ */
+	if (!msc->do_irq) {
+		kfree(mode);
+		return -EINVAL;
+	}
+
+	bdrv = msu_buffer_driver_get(mode);
+	kfree(mode);
+	if (bdrv)
+		goto found;
 
 	return -EINVAL;
 
 found:
 	mutex_lock(&msc->buf_mutex);
+	ret = 0;
+
+	/* Same buffer driver: do nothing */
+	if (bdrv && bdrv == msc->bdrv) {
+		/* matches try_module_get() in  msu_buffer_driver_get() */
+		module_put(bdrv->owner);
+		goto unlock;
+	}
+
 	ret = msc_buffer_unlocked_free_unless_used(msc);
-	if (!ret)
-		msc->mode = i;
+	if (ret)
+		goto unlock;
+
+	if (bdrv) {
+		void *bdrv_priv = bdrv->assign(dev, &i);
+
+		if (!bdrv_priv) {
+			ret = -ENOMEM;
+			goto unlock;
+		}
+
+		msc_buffer_unassign(msc);
+		msc->bdrv_priv = bdrv_priv;
+		msc->bdrv = bdrv;
+	} else {
+		msc_buffer_unassign(msc);
+	}
+
+	msc->mode = i;
+
+unlock:
+	if (ret && bdrv)
+		module_put(bdrv->owner);
 	mutex_unlock(&msc->buf_mutex);
 
 	return ret ? ret : size;
@@ -1668,7 +1982,12 @@ win_switch_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 
 	mutex_lock(&msc->buf_mutex);
-	if (msc->mode != MSC_MODE_MULTI)
+	/*
+	 * Window switch can only happen in the "multi" mode.
+	 * If a buffer driver is engaged, they have the full
+	 * control over window switching.
+	 */
+	if (msc->mode != MSC_MODE_MULTI || msc->bdrv)
 		ret = -ENOTSUPP;
 	else
 		msc_win_switch(msc);
@@ -1721,10 +2040,7 @@ static int intel_th_msc_probe(struct intel_th_device *thdev)
 	msc->reg_base = base + msc->index * 0x100;
 	msc->msu_base = base;
 
-	err = intel_th_msu_init(msc);
-	if (err)
-		return err;
-
+	INIT_WORK(&msc->work, msc_work);
 	err = intel_th_msc_init(msc);
 	if (err)
 		return err;
@@ -1740,7 +2056,6 @@ static void intel_th_msc_remove(struct intel_th_device *thdev)
 	int ret;
 
 	intel_th_msc_deactivate(thdev);
-	intel_th_msu_deinit(msc);
 
 	/*
 	 * Buffers should not be used at this point except if the
diff --git a/drivers/hwtracing/intel_th/msu.h b/drivers/hwtracing/intel_th/msu.h
index 574c16004cb2..acd808e316f9 100644
--- a/drivers/hwtracing/intel_th/msu.h
+++ b/drivers/hwtracing/intel_th/msu.h
@@ -44,14 +44,6 @@ enum {
 #define M0BLIE		BIT(16)
 #define M1BLIE		BIT(24)
 
-/* MSC operating modes (MSC_MODE) */
-enum {
-	MSC_MODE_SINGLE	= 0,
-	MSC_MODE_MULTI,
-	MSC_MODE_EXI,
-	MSC_MODE_DEBUG,
-};
-
 /* MSCnSTS bits */
 #define MSCSTS_WRAPSTAT	BIT(1)	/* Wrap occurred */
 #define MSCSTS_PLE	BIT(2)	/* Pipeline Empty */
@@ -93,6 +85,19 @@ static inline unsigned long msc_data_sz(struct msc_block_desc *bdesc)
 	return bdesc->valid_dw * 4 - MSC_BDESC;
 }
 
+static inline unsigned long msc_total_sz(struct msc_block_desc *bdesc)
+{
+	if (!bdesc->valid_dw)
+		return 0;
+
+	return bdesc->valid_dw * 4;
+}
+
+static inline unsigned long msc_block_sz(struct msc_block_desc *bdesc)
+{
+	return bdesc->block_sz * 64 - MSC_BDESC;
+}
+
 static inline bool msc_block_wrapped(struct msc_block_desc *bdesc)
 {
 	if (bdesc->hw_tag & (MSC_HW_TAG_BLOCKWRAP | MSC_HW_TAG_WINWRAP))
@@ -104,7 +109,7 @@ static inline bool msc_block_wrapped(struct msc_block_desc *bdesc)
 static inline bool msc_block_last_written(struct msc_block_desc *bdesc)
 {
 	if ((bdesc->hw_tag & MSC_HW_TAG_ENDBIT) ||
-	    (msc_data_sz(bdesc) != DATA_IN_PAGE))
+	    (msc_data_sz(bdesc) != msc_block_sz(bdesc)))
 		return true;
 
 	return false;
diff --git a/include/linux/intel_th.h b/include/linux/intel_th.h
new file mode 100644
index 000000000000..b00b7e1254d9
--- /dev/null
+++ b/include/linux/intel_th.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Intel(R) Trace Hub data structures for implementing buffer drivers.
+ *
+ * Copyright (C) 2019 Intel Corporation.
+ */
+
+#ifndef _INTEL_TH_H_
+#define _INTEL_TH_H_
+
+#include <linux/scatterlist.h>
+
+/* MSC operating modes (MSC_MODE) */
+enum {
+	MSC_MODE_SINGLE	= 0,
+	MSC_MODE_MULTI,
+	MSC_MODE_EXI,
+	MSC_MODE_DEBUG,
+};
+
+struct msu_buffer_driver {
+	const char	*name;
+	struct module	*owner;
+	/*
+	 * ->assign() called when buffer 'mode' is set to this driver
+	 *   (aka mode_store())
+	 * @device:	struct device * of the msc
+	 * @mode:	allows the driver to set HW mode (see the enum above)
+	 * Returns:	a pointer to a private structure associated with this
+	 *		msc or NULL in case of error. This private structure
+	 *		will then be passed into all other callbacks.
+	 */
+	void	*(*assign)(struct device *dev, int *mode);
+	/* ->unassign():	some other mode is selected, clean up */
+	void	(*unassign)(void *priv);
+	/*
+	 * ->alloc_window(): allocate memory for the window of a given
+	 *		size
+	 * @sgt:	pointer to sg_table, can be overridden by the buffer
+	 *		driver, or kept intact
+	 * Returns:	number of sg table entries <= number of pages;
+	 *		0 is treated as an allocation failure.
+	 */
+	int	(*alloc_window)(void *priv, struct sg_table **sgt,
+				size_t size);
+	void	(*free_window)(void *priv, struct sg_table *sgt);
+	/* ->activate():	trace has started */
+	void	(*activate)(void *priv);
+	/* ->deactivate():	trace is about to stop */
+	void	(*deactivate)(void *priv);
+	/*
+	 * ->ready():	window @sgt is filled up to the last block OR
+	 *		tracing is stopped by the user; this window contains
+	 *		@bytes data. The window in question transitions into
+	 *		the "LOCKED" state, indicating that it can't be used
+	 *		by hardware. To clear this state and make the window
+	 *		available to the hardware again, call
+	 *		intel_th_msc_window_unlock().
+	 */
+	int	(*ready)(void *priv, struct sg_table *sgt, size_t bytes);
+};
+
+int intel_th_msu_buffer_register(const struct msu_buffer_driver *bdrv);
+void intel_th_msu_buffer_unregister(const struct msu_buffer_driver *bdrv);
+void intel_th_msc_window_unlock(struct device *dev, struct sg_table *sgt);
+
+#endif /* _INTEL_TH_H_ */
-- 
2.20.1

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