intel_th: msu-sink: An example msu buffer "sink"

This patch adds an example MSU buffer "sink", which consumes trace
data from MSC buffers.

Functionally, it acts similarly to "multi" mode with automatic window
switching.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20190705141425.19894-3-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/intel_th/Makefile

@@ -20,3 +20,6 @@ intel_th_msu-y			:= msu.o
 
 obj-$(CONFIG_INTEL_TH_PTI)	+= intel_th_pti.o
 intel_th_pti-y			:= pti.o
+
+obj-$(CONFIG_INTEL_TH_MSU)	+= intel_th_msu_sink.o
+intel_th_msu_sink-y		:= msu-sink.o

drivers/hwtracing/intel_th/msu-sink.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * An example software sink buffer for Intel TH MSU.
+ *
+ * Copyright (C) 2019 Intel Corporation.
+ */
+
+#include <linux/intel_th.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/dma-mapping.h>
+
+#define MAX_SGTS 16
+
+struct msu_sink_private {
+	struct device	*dev;
+	struct sg_table **sgts;
+	unsigned int	nr_sgts;
+};
+
+static void *msu_sink_assign(struct device *dev, int *mode)
+{
+	struct msu_sink_private *priv;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return NULL;
+
+	priv->sgts = kcalloc(MAX_SGTS, sizeof(void *), GFP_KERNEL);
+	if (!priv->sgts) {
+		kfree(priv);
+		return NULL;
+	}
+
+	priv->dev = dev;
+	*mode = MSC_MODE_MULTI;
+
+	return priv;
+}
+
+static void msu_sink_unassign(void *data)
+{
+	struct msu_sink_private *priv = data;
+
+	kfree(priv->sgts);
+	kfree(priv);
+}
+
+/* See also: msc.c: __msc_buffer_win_alloc() */
+static int msu_sink_alloc_window(void *data, struct sg_table **sgt, size_t size)
+{
+	struct msu_sink_private *priv = data;
+	unsigned int nents;
+	struct scatterlist *sg_ptr;
+	void *block;
+	int ret, i;
+
+	if (priv->nr_sgts == MAX_SGTS)
+		return -ENOMEM;
+
+	nents = DIV_ROUND_UP(size, PAGE_SIZE);
+
+	ret = sg_alloc_table(*sgt, nents, GFP_KERNEL);
+	if (ret)
+		return -ENOMEM;
+
+	priv->sgts[priv->nr_sgts++] = *sgt;
+
+	for_each_sg((*sgt)->sgl, sg_ptr, nents, i) {
+		block = dma_alloc_coherent(priv->dev->parent->parent,
+					   PAGE_SIZE, &sg_dma_address(sg_ptr),
+					   GFP_KERNEL);
+		sg_set_buf(sg_ptr, block, PAGE_SIZE);
+	}
+
+	return nents;
+}
+
+/* See also: msc.c: __msc_buffer_win_free() */
+static void msu_sink_free_window(void *data, struct sg_table *sgt)
+{
+	struct msu_sink_private *priv = data;
+	struct scatterlist *sg_ptr;
+	int i;
+
+	for_each_sg(sgt->sgl, sg_ptr, sgt->nents, i) {
+		dma_free_coherent(priv->dev->parent->parent, PAGE_SIZE,
+				  sg_virt(sg_ptr), sg_dma_address(sg_ptr));
+	}
+
+	sg_free_table(sgt);
+	priv->nr_sgts--;
+}
+
+static int msu_sink_ready(void *data, struct sg_table *sgt, size_t bytes)
+{
+	struct msu_sink_private *priv = data;
+
+	intel_th_msc_window_unlock(priv->dev, sgt);
+
+	return 0;
+}
+
+static const struct msu_buffer sink_mbuf = {
+	.name		= "sink",
+	.assign		= msu_sink_assign,
+	.unassign	= msu_sink_unassign,
+	.alloc_window	= msu_sink_alloc_window,
+	.free_window	= msu_sink_free_window,
+	.ready		= msu_sink_ready,
+};
+
+module_intel_th_msu_buffer(sink_mbuf);
+
+MODULE_LICENSE("GPL v2");