interconnect: Add generic interconnect driver for Exynos SoCs

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 described by specifying in the 'interconnects' property
the interconnect consumer path for each interconnect provider DT node.

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 hard coded 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 samsung,data-clk-ratio DT property is used to specify the ratio
of the interconect bandwidth to the minimum data clock frequency
for each bus.

Due to unspecified relative probing order, -EPROBE_DEFER may be
propagated to ensure that the parent is probed before its children.

Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Artur Świgoń <a.swigon@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Link: https://lore.kernel.org/r/20201112140931.31139-3-s.nawrocki@samsung.com
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>

drivers/interconnect/Kconfig

@@ -13,5 +13,6 @@ if INTERCONNECT
 
 source "drivers/interconnect/imx/Kconfig"
 source "drivers/interconnect/qcom/Kconfig"
+source "drivers/interconnect/samsung/Kconfig"
 
 endif

drivers/interconnect/Makefile

@@ -6,3 +6,4 @@ icc-core-objs				:= core.o bulk.o
 obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
 obj-$(CONFIG_INTERCONNECT_IMX)		+= imx/
 obj-$(CONFIG_INTERCONNECT_QCOM)		+= qcom/
+obj-$(CONFIG_INTERCONNECT_SAMSUNG)	+= samsung/

drivers/interconnect/samsung/Kconfig

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config INTERCONNECT_SAMSUNG
+	bool "Samsung SoC interconnect drivers"
+	depends on ARCH_EXYNOS || COMPILE_TEST
+	help
+	  Interconnect drivers for Samsung SoCs.
+
+config INTERCONNECT_EXYNOS
+	tristate "Exynos generic interconnect driver"
+	depends on INTERCONNECT_SAMSUNG
+	default y if ARCH_EXYNOS
+	help
+	  Generic interconnect driver for Exynos SoCs.

drivers/interconnect/samsung/Makefile

@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+exynos-interconnect-objs		:= exynos.o
+
+obj-$(CONFIG_INTERCONNECT_EXYNOS)	+= exynos-interconnect.o

drivers/interconnect/samsung/exynos.c

@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Exynos generic interconnect provider driver
+ *
+ * Copyright (c) 2020 Samsung Electronics Co., Ltd.
+ *
+ * Authors: Artur Świgoń <a.swigon@samsung.com>
+ *          Sylwester Nawrocki <s.nawrocki@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>
+#include <linux/slab.h>
+
+#define EXYNOS_ICC_DEFAULT_BUS_CLK_RATIO	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_clk_ratio;
+};
+
+static struct icc_node *exynos_icc_get_parent(struct device_node *np)
+{
+	struct of_phandle_args args;
+	struct icc_node_data *icc_node_data;
+	struct icc_node *icc_node;
+	int num, ret;
+
+	num = of_count_phandle_with_args(np, "interconnects",
+					 "#interconnect-cells");
+	if (num < 1)
+		return NULL; /* parent nodes are optional */
+
+	/* Get the interconnect target node */
+	ret = of_parse_phandle_with_args(np, "interconnects",
+					"#interconnect-cells", 0, &args);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	icc_node_data = of_icc_get_from_provider(&args);
+	of_node_put(args.np);
+
+	if (IS_ERR(icc_node_data))
+		return ERR_CAST(icc_node_data);
+
+	icc_node = icc_node_data->node;
+	kfree(icc_node_data);
+
+	return icc_node;
+}
+
+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_clk_ratio;
+	s32 dst_freq = max(dst->avg_bw, dst->peak_bw) / dst_priv->bus_clk_ratio;
+	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 (src)\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 (dst)\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 (parent_node && !IS_ERR(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, "samsung,data-clock-ratio",
+				 &priv->bus_clk_ratio))
+		priv->bus_clk_ratio = EXYNOS_ICC_DEFAULT_BUS_CLK_RATIO;
+
+	/*
+	 * Register a PM QoS request for the parent (devfreq) device.
+	 */
+	ret = dev_pm_qos_add_request(bus_dev, &priv->qos_req,
+				     DEV_PM_QOS_MIN_FREQUENCY, 0);
+	if (ret < 0)
+		goto err_node_del;
+
+	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_pmqos_del;
+	}
+	if (icc_parent_node) {
+		ret = icc_link_create(icc_node, icc_parent_node->id);
+		if (ret < 0)
+			goto err_pmqos_del;
+	}
+
+	return 0;
+
+err_pmqos_del:
+	dev_pm_qos_remove_request(&priv->qos_req);
+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",
+		.sync_state = icc_sync_state,
+	},
+	.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@samsung.com>");
+MODULE_AUTHOR("Sylwester Nawrocki <s.nawrocki@samsung.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:exynos-generic-icc");