[PATCH v2 10/12] coresight: tmc-etr: Add transparent buffer management

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, mathieu.poirier@linaro.org,
	mike.leach@linaro.org, robert.walker@arm.com,
	coresight@lists.linaro.org, devicetree@vger.kernel.org,
	robh@kernel.org, frowand.list@gmail.com,
	Suzuki K Poulose <suzuki.poulose@arm.com>
Subject: [PATCH v2 10/12] coresight: tmc-etr: Add transparent buffer management
Date: Tue, 29 May 2018 14:15:35 +0100	[thread overview]
Message-ID: <1527599737-28408-11-git-send-email-suzuki.poulose@arm.com> (raw)
In-Reply-To: <1527599737-28408-1-git-send-email-suzuki.poulose@arm.com>

The TMC-ETR can use the target trace buffer in two different modes.
Normal physically contiguous mode and a discontiguous list pages in
Scatter-Gather mode. Also we have dedicated Coresight component, CATU
(Coresight Address Translation Unit) to provide improved scatter-gather
mode in Coresight SoC-600. This complicates the management of the
buffer used for trace, depending on the mode in which ETR is configured.

So, this patch adds a transparent layer for managing the ETR buffer
which abstracts the basic operations on the buffer (alloc, free,
sync and retrieve the data) and uses the mode specific helpers to
do the actual operation. This also allows the ETR driver to choose
the best mode for a given use case and adds the flexibility to
fallback to a different mode, without duplicating the code.

The patch also adds the "normal" flat memory mode and switches
the sysfs driver to use the new layer.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes since last version:
 - Split the SG mode support to a separate patch
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 342 ++++++++++++++++++------
 drivers/hwtracing/coresight/coresight-tmc.h     |  55 +++-
 2 files changed, 308 insertions(+), 89 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 67b4117..a0e504a 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -6,10 +6,18 @@
 
 #include <linux/coresight.h>
 #include <linux/dma-mapping.h>
+#include <linux/iommu.h>
 #include <linux/slab.h>
 #include "coresight-priv.h"
 #include "coresight-tmc.h"
 
+struct etr_flat_buf {
+	struct device	*dev;
+	dma_addr_t	daddr;
+	void		*vaddr;
+	size_t		size;
+};
+
 /*
  * The TMC ETR SG has a page size of 4K. The SG table contains pointers
  * to 4KB buffers. However, the OS may use a PAGE_SIZE different from
@@ -540,16 +548,207 @@ tmc_init_etr_sg_table(struct device *dev, int node,
 	return etr_table;
 }
 
+/*
+ * tmc_etr_alloc_flat_buf: Allocate a contiguous DMA buffer.
+ */
+static int tmc_etr_alloc_flat_buf(struct tmc_drvdata *drvdata,
+				  struct etr_buf *etr_buf, int node,
+				  void **pages)
+{
+	struct etr_flat_buf *flat_buf;
+
+	/* We cannot reuse existing pages for flat buf */
+	if (pages)
+		return -EINVAL;
+
+	flat_buf = kzalloc(sizeof(*flat_buf), GFP_KERNEL);
+	if (!flat_buf)
+		return -ENOMEM;
+
+	flat_buf->vaddr = dma_alloc_coherent(drvdata->dev, etr_buf->size,
+					     &flat_buf->daddr, GFP_KERNEL);
+	if (!flat_buf->vaddr) {
+		kfree(flat_buf);
+		return -ENOMEM;
+	}
+
+	flat_buf->size = etr_buf->size;
+	flat_buf->dev = drvdata->dev;
+	etr_buf->hwaddr = flat_buf->daddr;
+	etr_buf->mode = ETR_MODE_FLAT;
+	etr_buf->private = flat_buf;
+	return 0;
+}
+
+static void tmc_etr_free_flat_buf(struct etr_buf *etr_buf)
+{
+	struct etr_flat_buf *flat_buf = etr_buf->private;
+
+	if (flat_buf && flat_buf->daddr)
+		dma_free_coherent(flat_buf->dev, flat_buf->size,
+				  flat_buf->vaddr, flat_buf->daddr);
+	kfree(flat_buf);
+}
+
+static void tmc_etr_sync_flat_buf(struct etr_buf *etr_buf, u64 rrp, u64 rwp)
+{
+	/*
+	 * Adjust the buffer to point to the beginning of the trace data
+	 * and update the available trace data.
+	 */
+	etr_buf->offset = rrp - etr_buf->hwaddr;
+	if (etr_buf->full)
+		etr_buf->len = etr_buf->size;
+	else
+		etr_buf->len = rwp - rrp;
+}
+
+static ssize_t tmc_etr_get_data_flat_buf(struct etr_buf *etr_buf,
+					 u64 offset, size_t len, char **bufpp)
+{
+	struct etr_flat_buf *flat_buf = etr_buf->private;
+
+	*bufpp = (char *)flat_buf->vaddr + offset;
+	/*
+	 * tmc_etr_buf_get_data already adjusts the length to handle
+	 * buffer wrapping around.
+	 */
+	return len;
+}
+
+static const struct etr_buf_operations etr_flat_buf_ops = {
+	.alloc = tmc_etr_alloc_flat_buf,
+	.free = tmc_etr_free_flat_buf,
+	.sync = tmc_etr_sync_flat_buf,
+	.get_data = tmc_etr_get_data_flat_buf,
+};
+
+static const struct etr_buf_operations *etr_buf_ops[] = {
+	[ETR_MODE_FLAT] = &etr_flat_buf_ops,
+};
+
+static inline int tmc_etr_mode_alloc_buf(int mode,
+					 struct tmc_drvdata *drvdata,
+					 struct etr_buf *etr_buf, int node,
+					 void **pages)
+{
+	int rc;
+
+	switch (mode) {
+	case ETR_MODE_FLAT:
+		rc = etr_buf_ops[mode]->alloc(drvdata, etr_buf, node, pages);
+		if (!rc)
+			etr_buf->ops = etr_buf_ops[mode];
+		return rc;
+	default:
+		return -EINVAL;
+	}
+}
+
+/*
+ * tmc_alloc_etr_buf: Allocate a buffer use by ETR.
+ * @drvdata	: ETR device details.
+ * @size	: size of the requested buffer.
+ * @flags	: Required properties for the buffer.
+ * @node	: Node for memory allocations.
+ * @pages	: An optional list of pages.
+ */
+static struct etr_buf *tmc_alloc_etr_buf(struct tmc_drvdata *drvdata,
+					 ssize_t size, int flags,
+					 int node, void **pages)
+{
+	int rc = 0;
+	struct etr_buf *etr_buf;
+
+	etr_buf = kzalloc(sizeof(*etr_buf), GFP_KERNEL);
+	if (!etr_buf)
+		return ERR_PTR(-ENOMEM);
+
+	etr_buf->size = size;
+
+	rc = tmc_etr_mode_alloc_buf(ETR_MODE_FLAT, drvdata,
+				    etr_buf, node, pages);
+	if (rc) {
+		kfree(etr_buf);
+		return ERR_PTR(rc);
+	}
+
+	return etr_buf;
+}
+
+static void tmc_free_etr_buf(struct etr_buf *etr_buf)
+{
+	WARN_ON(!etr_buf->ops || !etr_buf->ops->free);
+	etr_buf->ops->free(etr_buf);
+	kfree(etr_buf);
+}
+
+/*
+ * tmc_etr_buf_get_data: Get the pointer the trace data at @offset
+ * with a maximum of @len bytes.
+ * Returns: The size of the linear data available @pos, with *bufpp
+ * updated to point to the buffer.
+ */
+static ssize_t tmc_etr_buf_get_data(struct etr_buf *etr_buf,
+				    u64 offset, size_t len, char **bufpp)
+{
+	/* Adjust the length to limit this transaction to end of buffer */
+	len = (len < (etr_buf->size - offset)) ? len : etr_buf->size - offset;
+
+	return etr_buf->ops->get_data(etr_buf, (u64)offset, len, bufpp);
+}
+
+static inline s64
+tmc_etr_buf_insert_barrier_packet(struct etr_buf *etr_buf, u64 offset)
+{
+	ssize_t len;
+	char *bufp;
+
+	len = tmc_etr_buf_get_data(etr_buf, offset,
+				   CORESIGHT_BARRIER_PKT_SIZE, &bufp);
+	if (WARN_ON(len <= CORESIGHT_BARRIER_PKT_SIZE))
+		return -EINVAL;
+	coresight_insert_barrier_packet(bufp);
+	return offset + CORESIGHT_BARRIER_PKT_SIZE;
+}
+
+/*
+ * tmc_sync_etr_buf: Sync the trace buffer availability with drvdata.
+ * Makes sure the trace data is synced to the memory for consumption.
+ * @etr_buf->offset will hold the offset to the beginning of the trace data
+ * within the buffer, with @etr_buf->len bytes to consume.
+ */
+static void tmc_sync_etr_buf(struct tmc_drvdata *drvdata)
+{
+	struct etr_buf *etr_buf = drvdata->etr_buf;
+	u64 rrp, rwp;
+	u32 status;
+
+	rrp = tmc_read_rrp(drvdata);
+	rwp = tmc_read_rwp(drvdata);
+	status = readl_relaxed(drvdata->base + TMC_STS);
+	etr_buf->full = status & TMC_STS_FULL;
+
+	WARN_ON(!etr_buf->ops || !etr_buf->ops->sync);
+
+	etr_buf->ops->sync(etr_buf, rrp, rwp);
+
+	/* Insert barrier packets at the beginning, if there was an overflow */
+	if (etr_buf->full)
+		tmc_etr_buf_insert_barrier_packet(etr_buf, etr_buf->offset);
+}
+
 static void tmc_etr_enable_hw(struct tmc_drvdata *drvdata)
 {
 	u32 axictl, sts;
+	struct etr_buf *etr_buf = drvdata->etr_buf;
 
 	CS_UNLOCK(drvdata->base);
 
 	/* Wait for TMCSReady bit to be set */
 	tmc_wait_for_tmcready(drvdata);
 
-	writel_relaxed(drvdata->size / 4, drvdata->base + TMC_RSZ);
+	writel_relaxed(etr_buf->size / 4, drvdata->base + TMC_RSZ);
 	writel_relaxed(TMC_MODE_CIRCULAR_BUFFER, drvdata->base + TMC_MODE);
 
 	axictl = readl_relaxed(drvdata->base + TMC_AXICTL);
@@ -563,15 +762,15 @@ static void tmc_etr_enable_hw(struct tmc_drvdata *drvdata)
 	}
 
 	writel_relaxed(axictl, drvdata->base + TMC_AXICTL);
-	tmc_write_dba(drvdata, drvdata->paddr);
+	tmc_write_dba(drvdata, etr_buf->hwaddr);
 	/*
 	 * If the TMC pointers must be programmed before the session,
 	 * we have to set it properly (i.e, RRP/RWP to base address and
 	 * STS to "not full").
 	 */
 	if (tmc_etr_has_cap(drvdata, TMC_ETR_SAVE_RESTORE)) {
-		tmc_write_rrp(drvdata, drvdata->paddr);
-		tmc_write_rwp(drvdata, drvdata->paddr);
+		tmc_write_rrp(drvdata, etr_buf->hwaddr);
+		tmc_write_rwp(drvdata, etr_buf->hwaddr);
 		sts = readl_relaxed(drvdata->base + TMC_STS) & ~TMC_STS_FULL;
 		writel_relaxed(sts, drvdata->base + TMC_STS);
 	}
@@ -587,59 +786,48 @@ static void tmc_etr_enable_hw(struct tmc_drvdata *drvdata)
 }
 
 /*
- * Return the available trace data in the buffer @pos, with a maximum
- * limit of @len, also updating the @bufpp on where to find it.
+ * Return the available trace data in the buffer (starts at etr_buf->offset,
+ * limited by etr_buf->len) from @pos, with a maximum limit of @len,
+ * also updating the @bufpp on where to find it. Since the trace data
+ * starts at anywhere in the buffer, depending on the RRP, we adjust the
+ * @len returned to handle buffer wrapping around.
  */
 ssize_t tmc_etr_get_sysfs_trace(struct tmc_drvdata *drvdata,
 				loff_t pos, size_t len, char **bufpp)
 {
+	s64 offset;
 	ssize_t actual = len;
-	char *bufp = drvdata->buf + pos;
-	char *bufend = (char *)(drvdata->vaddr + drvdata->size);
-
-	/* Adjust the len to available size @pos */
-	if (pos + actual > drvdata->len)
-		actual = drvdata->len - pos;
+	struct etr_buf *etr_buf = drvdata->etr_buf;
 
+	if (pos + actual > etr_buf->len)
+		actual = etr_buf->len - pos;
 	if (actual <= 0)
 		return actual;
 
-	/*
-	 * Since we use a circular buffer, with trace data starting
-	 * @drvdata->buf, possibly anywhere in the buffer @drvdata->vaddr,
-	 * wrap the current @pos to within the buffer.
-	 */
-	if (bufp >= bufend)
-		bufp -= drvdata->size;
-	/*
-	 * For simplicity, avoid copying over a wrapped around buffer.
-	 */
-	if ((bufp + actual) > bufend)
-		actual = bufend - bufp;
-	*bufpp = bufp;
-	return actual;
+	/* Compute the offset from which we read the data */
+	offset = etr_buf->offset + pos;
+	if (offset >= etr_buf->size)
+		offset -= etr_buf->size;
+	return tmc_etr_buf_get_data(etr_buf, offset, actual, bufpp);
 }
 
-static void tmc_etr_dump_hw(struct tmc_drvdata *drvdata)
+static struct etr_buf *
+tmc_etr_setup_sysfs_buf(struct tmc_drvdata *drvdata)
 {
-	u32 val;
-	u64 rwp;
+	return tmc_alloc_etr_buf(drvdata, drvdata->size,
+				 0, cpu_to_node(0), NULL);
+}
 
-	rwp = tmc_read_rwp(drvdata);
-	val = readl_relaxed(drvdata->base + TMC_STS);
+static void
+tmc_etr_free_sysfs_buf(struct etr_buf *buf)
+{
+	if (buf)
+		tmc_free_etr_buf(buf);
+}
 
-	/*
-	 * Adjust the buffer to point to the beginning of the trace data
-	 * and update the available trace data.
-	 */
-	if (val & TMC_STS_FULL) {
-		drvdata->buf = drvdata->vaddr + rwp - drvdata->paddr;
-		drvdata->len = drvdata->size;
-		coresight_insert_barrier_packet(drvdata->buf);
-	} else {
-		drvdata->buf = drvdata->vaddr;
-		drvdata->len = rwp - drvdata->paddr;
-	}
+static void tmc_etr_sync_sysfs_buf(struct tmc_drvdata *drvdata)
+{
+	tmc_sync_etr_buf(drvdata);
 }
 
 static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
@@ -652,7 +840,8 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
 	 * read before the TMC is disabled.
 	 */
 	if (drvdata->mode == CS_MODE_SYSFS)
-		tmc_etr_dump_hw(drvdata);
+		tmc_etr_sync_sysfs_buf(drvdata);
+
 	tmc_disable_hw(drvdata);
 
 	CS_LOCK(drvdata->base);
@@ -661,35 +850,32 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
 static int tmc_enable_etr_sink_sysfs(struct coresight_device *csdev)
 {
 	int ret = 0;
-	bool used = false;
 	unsigned long flags;
-	void __iomem *vaddr = NULL;
-	dma_addr_t paddr = 0;
 	struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+	struct etr_buf *new_buf = NULL, *free_buf = NULL;
 
 	/*
-	 * If we don't have a buffer release the lock and allocate memory.
-	 * Otherwise keep the lock and move along.
+	 * If we are enabling the ETR from disabled state, we need to make
+	 * sure we have a buffer with the right size. The etr_buf is not reset
+	 * immediately after we stop the tracing in SYSFS mode as we wait for
+	 * the user to collect the data. We may be able to reuse the existing
+	 * buffer, provided the size matches. Any allocation has to be done
+	 * with the lock released.
 	 */
 	spin_lock_irqsave(&drvdata->spinlock, flags);
-	if (!drvdata->vaddr) {
+	if (!drvdata->etr_buf || (drvdata->etr_buf->size != drvdata->size)) {
 		spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
-		/*
-		 * Contiguous  memory can't be allocated while a spinlock is
-		 * held.  As such allocate memory here and free it if a buffer
-		 * has already been allocated (from a previous session).
-		 */
-		vaddr = dma_alloc_coherent(drvdata->dev, drvdata->size,
-					   &paddr, GFP_KERNEL);
-		if (!vaddr)
-			return -ENOMEM;
+		/* Allocate memory with the locks released */
+		free_buf = new_buf = tmc_etr_setup_sysfs_buf(drvdata);
+		if (IS_ERR(new_buf))
+			return PTR_ERR(new_buf);
 
 		/* Let's try again */
 		spin_lock_irqsave(&drvdata->spinlock, flags);
 	}
 
-	if (drvdata->reading) {
+	if (drvdata->reading || drvdata->mode == CS_MODE_PERF) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -697,21 +883,19 @@ static int tmc_enable_etr_sink_sysfs(struct coresight_device *csdev)
 	/*
 	 * In sysFS mode we can have multiple writers per sink.  Since this
 	 * sink is already enabled no memory is needed and the HW need not be
-	 * touched.
+	 * touched, even if the buffer size has changed.
 	 */
 	if (drvdata->mode == CS_MODE_SYSFS)
 		goto out;
 
 	/*
-	 * If drvdata::vaddr == NULL, use the memory allocated above.
-	 * Otherwise a buffer still exists from a previous session, so
-	 * simply use that.
+	 * If we don't have a buffer or it doesn't match the requested size,
+	 * use the buffer allocated above. Otherwise reuse the existing buffer.
 	 */
-	if (drvdata->vaddr == NULL) {
-		used = true;
-		drvdata->vaddr = vaddr;
-		drvdata->paddr = paddr;
-		drvdata->buf = drvdata->vaddr;
+	if (!drvdata->etr_buf ||
+	    (new_buf && drvdata->etr_buf->size != new_buf->size)) {
+		free_buf = drvdata->etr_buf;
+		drvdata->etr_buf = new_buf;
 	}
 
 	drvdata->mode = CS_MODE_SYSFS;
@@ -720,8 +904,8 @@ static int tmc_enable_etr_sink_sysfs(struct coresight_device *csdev)
 	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
 	/* Free memory outside the spinlock if need be */
-	if (!used && vaddr)
-		dma_free_coherent(drvdata->dev, drvdata->size, vaddr, paddr);
+	if (free_buf)
+		tmc_etr_free_sysfs_buf(free_buf);
 
 	if (!ret)
 		dev_info(drvdata->dev, "TMC-ETR enabled\n");
@@ -800,8 +984,8 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
 		goto out;
 	}
 
-	/* If drvdata::buf is NULL the trace data has been read already */
-	if (drvdata->buf == NULL) {
+	/* If drvdata::etr_buf is NULL the trace data has been read already */
+	if (drvdata->etr_buf == NULL) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -820,8 +1004,7 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
 int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
 {
 	unsigned long flags;
-	dma_addr_t paddr;
-	void __iomem *vaddr = NULL;
+	struct etr_buf *etr_buf = NULL;
 
 	/* config types are set a boot time and never change */
 	if (WARN_ON_ONCE(drvdata->config_type != TMC_CONFIG_TYPE_ETR))
@@ -842,17 +1025,16 @@ int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
 		 * The ETR is not tracing and the buffer was just read.
 		 * As such prepare to free the trace buffer.
 		 */
-		vaddr = drvdata->vaddr;
-		paddr = drvdata->paddr;
-		drvdata->buf = drvdata->vaddr = NULL;
+		etr_buf =  drvdata->etr_buf;
+		drvdata->etr_buf = NULL;
 	}
 
 	drvdata->reading = false;
 	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
 	/* Free allocated memory out side of the spinlock */
-	if (vaddr)
-		dma_free_coherent(drvdata->dev, drvdata->size, vaddr, paddr);
+	if (etr_buf)
+		tmc_free_etr_buf(etr_buf);
 
 	return 0;
 }
diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index cdb668b..39ed306 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -123,6 +123,34 @@ enum tmc_mem_intf_width {
 #define CORESIGHT_SOC_600_ETR_CAPS	\
 	(TMC_ETR_SAVE_RESTORE | TMC_ETR_AXI_ARCACHE)
 
+enum etr_mode {
+	ETR_MODE_FLAT,		/* Uses contiguous flat buffer */
+};
+
+struct etr_buf_operations;
+
+/**
+ * struct etr_buf - Details of the buffer used by ETR
+ * @mode	: Mode of the ETR buffer, contiguous, Scatter Gather etc.
+ * @full	: Trace data overflow
+ * @size	: Size of the buffer.
+ * @hwaddr	: Address to be programmed in the TMC:DBA{LO,HI}
+ * @offset	: Offset of the trace data in the buffer for consumption.
+ * @len		: Available trace data @buf (may round up to the beginning).
+ * @ops		: ETR buffer operations for the mode.
+ * @private	: Backend specific information for the buf
+ */
+struct etr_buf {
+	enum etr_mode			mode;
+	bool				full;
+	ssize_t				size;
+	dma_addr_t			hwaddr;
+	unsigned long			offset;
+	s64				len;
+	const struct etr_buf_operations	*ops;
+	void				*private;
+};
+
 /**
  * struct tmc_drvdata - specifics associated to an TMC component
  * @base:	memory mapped base address for this component.
@@ -130,11 +158,10 @@ enum tmc_mem_intf_width {
  * @csdev:	component vitals needed by the framework.
  * @miscdev:	specifics to handle "/dev/xyz.tmc" entry.
  * @spinlock:	only one at a time pls.
- * @buf:	area of memory where trace data get sent.
- * @paddr:	DMA start location in RAM.
- * @vaddr:	virtual representation of @paddr.
- * @size:	trace buffer size.
- * @len:	size of the available trace.
+ * @buf:	Snapshot of the trace data for ETF/ETB.
+ * @etr_buf:	details of buffer used in TMC-ETR
+ * @len:	size of the available trace for ETF/ETB.
+ * @size:	trace buffer size for this TMC (common for all modes).
  * @mode:	how this TMC is being used.
  * @config_type: TMC variant, must be of type @tmc_config_type.
  * @memwidth:	width of the memory interface databus, in bytes.
@@ -149,11 +176,12 @@ struct tmc_drvdata {
 	struct miscdevice	miscdev;
 	spinlock_t		spinlock;
 	bool			reading;
-	char			*buf;
-	dma_addr_t		paddr;
-	void __iomem		*vaddr;
-	u32			size;
+	union {
+		char		*buf;		/* TMC ETB */
+		struct etr_buf	*etr_buf;	/* TMC ETR */
+	};
 	u32			len;
+	u32			size;
 	u32			mode;
 	enum tmc_config_type	config_type;
 	enum tmc_mem_intf_width	memwidth;
@@ -161,6 +189,15 @@ struct tmc_drvdata {
 	u32			etr_caps;
 };
 
+struct etr_buf_operations {
+	int (*alloc)(struct tmc_drvdata *drvdata, struct etr_buf *etr_buf,
+			int node, void **pages);
+	void (*sync)(struct etr_buf *etr_buf, u64 rrp, u64 rwp);
+	ssize_t (*get_data)(struct etr_buf *etr_buf, u64 offset, size_t len,
+				char **bufpp);
+	void (*free)(struct etr_buf *etr_buf);
+};
+
 /**
  * struct tmc_pages - Collection of pages used for SG.
  * @nr_pages:		Number of pages in the list.
-- 
2.7.4
