coresight: tmc: Hide trace buffer handling for file read

At the moment we adjust the buffer pointers for reading the trace
data via misc device in the common code for ETF/ETB and ETR. Since
we are going to change how we manage the buffer for ETR, let us
move the buffer manipulation to the respective driver files, hiding
it from the common code. We do so by adding type specific helpers
for finding the length of data and the pointer to the buffer,
for a given length at a file position.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 02f747afa2ba..f88342d400ef 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -58,6 +58,40 @@ static void tmc_etr_enable_hw(struct tmc_drvdata *drvdata)
 	CS_LOCK(drvdata->base);
 }
 
+/*
+ * Return the available trace data in the buffer @pos, with a maximum
+ * limit of @len, also updating the @bufpp on where to find it.
+ */
+ssize_t tmc_etr_get_sysfs_trace(struct tmc_drvdata *drvdata,
+				loff_t pos, size_t len, char **bufpp)
+{
+	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;
+
+	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;
+}
+
 static void tmc_etr_dump_hw(struct tmc_drvdata *drvdata)
 {
 	const u32 *barrier;