[PATCH v21 3/8] coresight: tmc: add a function to switch the ETR to a free etr_buf

[Jie Gan <jie.gan@oss.qualcomm.com>]

Add tmc_etr_switch_buf_node() to switch the ETR to a free etr_buf of the
etr_buf_list without disabling the sink. It returns the node of the
switched out etr_buf, so its synced data can be read while the ETR keeps
tracing into the new one.

Stopping the ETR, swapping the etr_buf and restarting the ETR have to be
done in one critical section. Otherwise tmc_disable_etr_sink() can run
in between and leave drvdata->etr_buf out of sync with the hardware.
Provide the sequence as a TMC helper, so callers don't need to know
about the locking of the ETR state.

Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 65 +++++++++++++++++++++++++
 drivers/hwtracing/coresight/coresight-tmc.h     |  4 ++
 2 files changed, 69 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index eee98a9269df..2de31d73a4b4 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1224,6 +1224,71 @@ static void __tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
 
 }
 
+static void tmc_etr_reset_sysfs_buf(struct tmc_drvdata *drvdata)
+{
+	u32 sts;
+
+	CS_UNLOCK(drvdata->base);
+	tmc_write_rrp(drvdata, drvdata->sysfs_buf->hwaddr);
+	tmc_write_rwp(drvdata, drvdata->sysfs_buf->hwaddr);
+	sts = readl_relaxed(drvdata->base + TMC_STS) & ~TMC_STS_FULL;
+	writel_relaxed(sts, drvdata->base + TMC_STS);
+	CS_LOCK(drvdata->base);
+}
+
+/**
+ * tmc_etr_switch_buf_node - switch the ETR to a free buffer of the etr_buf_list.
+ * @drvdata:	drvdata of the TMC device.
+ *
+ * Stop the ETR, hand over the current buffer for reading, switch to a free
+ * buffer and restart the ETR. All of this is done with @drvdata->spinlock held,
+ * so it can't race with the sink disable path.
+ *
+ * Return: the node of the switched out buffer, or NULL if the sink isn't in
+ * sysfs mode or there is no free buffer. The ETR is left untouched in both
+ * cases.
+ */
+struct etr_buf_node *tmc_etr_switch_buf_node(struct tmc_drvdata *drvdata)
+{
+	struct etr_buf_node *nd, *curr_node = NULL, *picked_node = NULL;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&drvdata->spinlock, flags);
+	if (coresight_get_mode(drvdata->csdev) != CS_MODE_SYSFS)
+		goto out;
+
+	list_for_each_entry(nd, &drvdata->etr_buf_list, link) {
+		if (nd->sysfs_buf == drvdata->sysfs_buf)
+			curr_node = nd;
+		else if (!picked_node && nd->is_free)
+			picked_node = nd;
+	}
+
+	if (!curr_node || !picked_node) {
+		curr_node = NULL;
+		goto out;
+	}
+
+	__tmc_etr_disable_hw(drvdata);
+
+	/* The switched out buffer is free again once it has been read */
+	curr_node->is_free = true;
+	curr_node->pos = 0;
+	curr_node->reading = true;
+	picked_node->is_free = false;
+	drvdata->sysfs_buf = picked_node->sysfs_buf;
+	drvdata->etr_buf = picked_node->sysfs_buf;
+
+	tmc_etr_reset_sysfs_buf(drvdata);
+	if (__tmc_etr_enable_hw(drvdata))
+		dev_err(&drvdata->csdev->dev, "Failed to restart the ETR\n");
+out:
+	raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
+
+	return curr_node;
+}
+EXPORT_SYMBOL_GPL(tmc_etr_switch_buf_node);
+
 void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
 {
 	__tmc_etr_disable_hw(drvdata);
diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index 7c604b9f92e5..30b15c38b080 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -212,12 +212,15 @@ struct tmc_resrv_buf {
  * struct etr_buf_node - node of the etr_buf_list
  * @sysfs_buf:	Allocated sysfs_buf.
  * @is_free:	Indicates whether the buffer is free to choose.
+ * @reading:	Indicates the buffer attached to the node is being read by
+ *		the user.
  * @pos:	Offset to the start of the buffer.
  * @link:	list_head of the node.
  */
 struct etr_buf_node {
 	struct etr_buf		*sysfs_buf;
 	bool			is_free;
+	bool			reading;
 	loff_t			pos;
 	struct list_head	link;
 };
@@ -465,5 +468,6 @@ struct etr_buf *tmc_etr_get_buffer(struct coresight_device *csdev,
 extern const struct attribute_group coresight_etr_group;
 void tmc_clean_etr_buf_list(struct tmc_drvdata *drvdata);
 int tmc_create_etr_buf_list(struct tmc_drvdata *drvdata, int num_nodes);
+struct etr_buf_node *tmc_etr_switch_buf_node(struct tmc_drvdata *drvdata);
 
 #endif

-- 
2.34.1