[PATCH RFC v6 2/6] interconnect: Add generic interconnect driver for Exynos SoCs

[Sylwester Nawrocki]

This patch adds a generic interconnect driver for Exynos SoCs in order
to provide interconnect functionality for each "samsung,exynos-bus"
compatible device.

The SoC topology is a graph (or more specifically, a tree) and its
edges are specified using the 'samsung,interconnect-parent' in the
DT. Due to unspecified relative probing order, -EPROBE_DEFER may be
propagated to ensure that the parent is probed before its children.

Each bus is now an interconnect provider and an interconnect node as
well (cf. Documentation/interconnect/interconnect.rst), i.e. every bus
registers itself as a node. Node IDs are not hardcoded but rather
assigned dynamically at runtime. This approach allows for using this
driver with various Exynos SoCs.

Frequencies requested via the interconnect API for a given node are
propagated to devfreq using dev_pm_qos_update_request(). Please note
that it is not an error when CONFIG_INTERCONNECT is 'n', in which
case all interconnect API functions are no-op.

The bus-width DT property is to determine the interconnect data
width and traslate requested bandwidth to clock frequency for each
bus.

Signed-off-by: Artur Świgoń <a.swigon at samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
---
Changes for v6:
 - corrected of_node dereferencing in exynos_icc_get_parent()
   function,
 - corrected initialization of icc_node->name so as to avoid
   direct of_node->name dereferencing,
 - added parsing of bus-width DT property,
 - use IS_ERR_OR_NULL in exynos_icc_genberic_remove().

Changes for v5:
 - adjust to renamed exynos,interconnect-parent-node property,
 - use automatically generated platform device id as the interconect
   node id instead of a now unavailable devfreq->id field,
 - add icc_ prefix to some variables to make the code more self-commenting,
 - use icc_nodes_remove() instead of icc_node_del() + icc_node_destroy(),
 - adjust to exynos,interconnect-parent-node property rename to
   samsung,interconnect-parent,
 - converted to a separate platform driver in drivers/interconnect.
---
 drivers/interconnect/Kconfig         |   1 +
 drivers/interconnect/Makefile        |   1 +
 drivers/interconnect/exynos/Kconfig  |   6 ++
 drivers/interconnect/exynos/Makefile |   4 +
 drivers/interconnect/exynos/exynos.c | 192 +++++++++++++++++++++++++++++++++++
 5 files changed, 204 insertions(+)
 create mode 100644 drivers/interconnect/exynos/Kconfig
 create mode 100644 drivers/interconnect/exynos/Makefile
 create mode 100644 drivers/interconnect/exynos/exynos.c

diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
index 5b7204e..eca6eda 100644
--- a/drivers/interconnect/Kconfig
+++ b/drivers/interconnect/Kconfig
@@ -11,6 +11,7 @@ menuconfig INTERCONNECT
 
 if INTERCONNECT
 
+source "drivers/interconnect/exynos/Kconfig"
 source "drivers/interconnect/imx/Kconfig"
 source "drivers/interconnect/qcom/Kconfig"
 
diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
index 4825c28..2ba1de6 100644
--- a/drivers/interconnect/Makefile
+++ b/drivers/interconnect/Makefile
@@ -4,5 +4,6 @@ CFLAGS_core.o				:= -I$(src)
 icc-core-objs				:= core.o
 
 obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
+obj-$(CONFIG_INTERCONNECT_EXYNOS)	+= exynos/
 obj-$(CONFIG_INTERCONNECT_IMX)		+= imx/
 obj-$(CONFIG_INTERCONNECT_QCOM)		+= qcom/
diff --git a/drivers/interconnect/exynos/Kconfig b/drivers/interconnect/exynos/Kconfig
new file mode 100644
index 0000000..e51e52e
--- /dev/null
+++ b/drivers/interconnect/exynos/Kconfig
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config INTERCONNECT_EXYNOS
+	tristate "Exynos generic interconnect driver"
+	depends on ARCH_EXYNOS || COMPILE_TEST
+	help
+	  Generic interconnect driver for Exynos SoCs.
diff --git a/drivers/interconnect/exynos/Makefile b/drivers/interconnect/exynos/Makefile
new file mode 100644
index 0000000..e19d1df
--- /dev/null
+++ b/drivers/interconnect/exynos/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+exynos-interconnect-objs		:= exynos.o
+
+obj-$(CONFIG_INTERCONNECT_EXYNOS)	+= exynos-interconnect.o
diff --git a/drivers/interconnect/exynos/exynos.c b/drivers/interconnect/exynos/exynos.c
new file mode 100644
index 0000000..6c47a62
--- /dev/null
+++ b/drivers/interconnect/exynos/exynos.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Exynos generic interconnect provider driver
+ *
+ * Copyright (c) 2020 Samsung Electronics Co., Ltd.
+ *
+ * Authors: Artur Świgoń <a.swigon at samsung.com>
+ *          Sylwester Nawrocki <s.nawrocki at samsung.com>
+ */
+#include <linux/device.h>
+#include <linux/interconnect-provider.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pm_qos.h>
+
+#define EXYNOS_ICC_DEFAULT_BUS_WIDTH	8
+
+struct exynos_icc_priv {
+	struct device *dev;
+
+	/* One interconnect node per provider */
+	struct icc_provider provider;
+	struct icc_node *node;
+
+	struct dev_pm_qos_request qos_req;
+	u32 bus_width;
+};
+
+static struct icc_node *exynos_icc_get_parent(struct device_node *np)
+{
+	struct of_phandle_args args;
+	struct icc_node *icc_np;
+	int num, ret;
+
+	num = of_count_phandle_with_args(np, "samsung,interconnect-parent",
+					"#interconnect-cells");
+	if (num != 1)
+		return NULL; /* parent nodes are optional */
+
+	ret = of_parse_phandle_with_args(np, "samsung,interconnect-parent",
+					"#interconnect-cells", 0, &args);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	icc_np = of_icc_get_from_provider(&args);
+	of_node_put(args.np);
+
+	return icc_np;
+}
+
+static int exynos_generic_icc_set(struct icc_node *src, struct icc_node *dst)
+{
+	struct exynos_icc_priv *src_priv = src->data, *dst_priv = dst->data;
+	s32 src_freq = max(src->avg_bw, src->peak_bw) / src_priv->bus_width;
+	s32 dst_freq = max(dst->avg_bw, dst->peak_bw) / dst_priv->bus_width;
+	int ret;
+
+	ret = dev_pm_qos_update_request(&src_priv->qos_req, src_freq);
+	if (ret < 0) {
+		dev_err(src_priv->dev, "failed to update PM QoS of %s\n",
+			src->name);
+		return ret;
+	}
+
+	ret = dev_pm_qos_update_request(&dst_priv->qos_req, dst_freq);
+	if (ret < 0) {
+		dev_err(dst_priv->dev, "failed to update PM QoS of %s\n",
+			dst->name);
+		return ret;
+	}
+
+	return 0;
+}
+
+static struct icc_node *exynos_generic_icc_xlate(struct of_phandle_args *spec,
+						 void *data)
+{
+	struct exynos_icc_priv *priv = data;
+
+	if (spec->np != priv->dev->parent->of_node)
+		return ERR_PTR(-EINVAL);
+
+	return priv->node;
+}
+
+static int exynos_generic_icc_remove(struct platform_device *pdev)
+{
+	struct exynos_icc_priv *priv = platform_get_drvdata(pdev);
+	struct icc_node *parent_node, *node = priv->node;
+
+	parent_node = exynos_icc_get_parent(priv->dev->parent->of_node);
+	if (!IS_ERR_OR_NULL(parent_node))
+		icc_link_destroy(node, parent_node);
+
+	icc_nodes_remove(&priv->provider);
+	icc_provider_del(&priv->provider);
+
+	return 0;
+}
+
+static int exynos_generic_icc_probe(struct platform_device *pdev)
+{
+	struct device *bus_dev = pdev->dev.parent;
+	struct exynos_icc_priv *priv;
+	struct icc_provider *provider;
+	struct icc_node *icc_node, *icc_parent_node;
+	int ret;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->dev = &pdev->dev;
+	platform_set_drvdata(pdev, priv);
+
+	provider = &priv->provider;
+
+	provider->set = exynos_generic_icc_set;
+	provider->aggregate = icc_std_aggregate;
+	provider->xlate = exynos_generic_icc_xlate;
+	provider->dev = bus_dev;
+	provider->inter_set = true;
+	provider->data = priv;
+
+	ret = icc_provider_add(provider);
+	if (ret < 0)
+		return ret;
+
+	icc_node = icc_node_create(pdev->id);
+	if (IS_ERR(icc_node)) {
+		ret = PTR_ERR(icc_node);
+		goto err_prov_del;
+	}
+
+	priv->node = icc_node;
+	icc_node->name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "%pOFn",
+					bus_dev->of_node);
+	if (of_property_read_u32(bus_dev->of_node, "bus-width",
+				 &priv->bus_width))
+		priv->bus_width = EXYNOS_ICC_DEFAULT_BUS_WIDTH;
+
+	icc_node->data = priv;
+	icc_node_add(icc_node, provider);
+
+	icc_parent_node = exynos_icc_get_parent(bus_dev->of_node);
+	if (IS_ERR(icc_parent_node)) {
+		ret = PTR_ERR(icc_parent_node);
+		goto err_node_del;
+	}
+	if (icc_parent_node) {
+		ret = icc_link_create(icc_node, icc_parent_node->id);
+		if (ret < 0)
+			goto err_node_del;
+	}
+
+	/*
+	 * Register a PM QoS request for the bus device for which also devfreq
+	 * functionality is registered.
+	 */
+	ret = dev_pm_qos_add_request(bus_dev, &priv->qos_req,
+				     DEV_PM_QOS_MIN_FREQUENCY, 0);
+	if (ret < 0)
+		goto err_link_destroy;
+
+	return 0;
+
+err_link_destroy:
+	if (icc_parent_node)
+		icc_link_destroy(icc_node, icc_parent_node);
+err_node_del:
+	icc_nodes_remove(provider);
+err_prov_del:
+	icc_provider_del(provider);
+
+	return ret;
+}
+
+static struct platform_driver exynos_generic_icc_driver = {
+	.driver = {
+		.name = "exynos-generic-icc",
+	},
+	.probe = exynos_generic_icc_probe,
+	.remove = exynos_generic_icc_remove,
+};
+module_platform_driver(exynos_generic_icc_driver);
+
+MODULE_DESCRIPTION("Exynos generic interconnect driver");
+MODULE_AUTHOR("Artur Świgoń <a.swigon at samsung.com>");
+MODULE_AUTHOR("Sylwester Nawrocki <s.nawrocki at samsung.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:exynos-generic-icc");
-- 
2.7.4