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Subject: Re: [RFC PATCH v3 5/7] devfreq: exynos-bus: Add interconnect
 functionality to exynos-bus
To:     =?UTF-8?B?QXJ0dXIgxZp3aWdvxYQ=?= <a.swigon@samsung.com>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, dri-devel@lists.freedesktop.org
Cc:     cw00.choi@samsung.com, myungjoo.ham@samsung.com,
        inki.dae@samsung.com, sw0312.kim@samsung.com,
        leonard.crestez@nxp.com, m.szyprowski@samsung.com,
        b.zolnierkie@samsung.com, krzk@kernel.org
References: <20191220115653.6487-1-a.swigon@samsung.com>
 <CGME20191220120145eucas1p295af63eed7b23982d8c49fcf875cec8c@eucas1p2.samsung.com>
 <20191220115653.6487-6-a.swigon@samsung.com>
From:   Georgi Djakov <georgi.djakov@linaro.org>
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Message-ID: <15795421-db12-8466-bb7e-688e6625cf4a@linaro.org>
Date:   Wed, 22 Jan 2020 19:02:00 +0200
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In-Reply-To: <20191220115653.6487-6-a.swigon@samsung.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Artur,

On 12/20/19 13:56, Artur Świgoń wrote:
> This patch adds interconnect functionality to the exynos-bus devfreq
> driver.
> 
> The SoC topology is a graph (or, more specifically, a tree) and its
> edges are specified using the 'exynos,interconnect-parent-node' 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 at

Just to note that usually the provider consists of multiple nodes and each node
represents a single master or slave port on the AXI bus for example. I am not
sure whether this represents correctly the Exynos hardware, so it's up to
you.

> runtime, in probing order (subject to the above-mentioned exception
> regarding relative order). This approach allows for using this driver with
> various Exynos SoCs.

This sounds good. I am wondering whether such dynamic probing would be useful
for other platforms too. Then maybe it would make sense to even have a common DT
property, but we will see.

Is this going to be used only together with devfreq?

> 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.

How about the case where CONFIG_INTERCONNECT=m. Looks like the build will fail
if CONFIG_ARM_EXYNOS_BUS_DEVFREQ=y, so this dependency should be expressed in
Kconfig.

Thanks,
Georgi

> 
> Signed-off-by: Artur Świgoń <a.swigon@samsung.com>
> ---
>  drivers/devfreq/exynos-bus.c | 144 +++++++++++++++++++++++++++++++++++
>  1 file changed, 144 insertions(+)
> 
> diff --git a/drivers/devfreq/exynos-bus.c b/drivers/devfreq/exynos-bus.c
> index 9fdb188915e8..694a9581dcdb 100644
> --- a/drivers/devfreq/exynos-bus.c
> +++ b/drivers/devfreq/exynos-bus.c
> @@ -14,14 +14,19 @@
>  #include <linux/devfreq-event.h>
>  #include <linux/device.h>
>  #include <linux/export.h>
> +#include <linux/idr.h>
> +#include <linux/interconnect-provider.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_qos.h>
>  #include <linux/platform_device.h>
>  #include <linux/regulator/consumer.h>
>  
>  #define DEFAULT_SATURATION_RATIO	40
>  
> +#define kbps_to_khz(x) ((x) / 8)
> +
>  struct exynos_bus {
>  	struct device *dev;
>  
> @@ -35,6 +40,12 @@ struct exynos_bus {
>  	struct opp_table *opp_table;
>  	struct clk *clk;
>  	unsigned int ratio;
> +
> +	/* One provider per bus, one node per provider */
> +	struct icc_provider provider;
> +	struct icc_node *node;
> +
> +	struct dev_pm_qos_request qos_req;
>  };
>  
>  /*
> @@ -205,6 +216,39 @@ static void exynos_bus_passive_exit(struct device *dev)
>  	clk_disable_unprepare(bus->clk);
>  }
>  
> +static int exynos_bus_icc_set(struct icc_node *src, struct icc_node *dst)
> +{
> +	struct exynos_bus *src_bus = src->data, *dst_bus = dst->data;
> +	s32 src_freq = kbps_to_khz(src->avg_bw);
> +	s32 dst_freq = kbps_to_khz(dst->avg_bw);
> +	int ret;
> +
> +	ret = dev_pm_qos_update_request(&src_bus->qos_req, src_freq);
> +	if (ret < 0) {
> +		dev_err(src_bus->dev, "failed to update PM QoS request");
> +		return ret;
> +	}
> +
> +	ret = dev_pm_qos_update_request(&dst_bus->qos_req, dst_freq);
> +	if (ret < 0) {
> +		dev_err(dst_bus->dev, "failed to update PM QoS request");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct icc_node *exynos_bus_icc_xlate(struct of_phandle_args *spec,
> +					     void *data)
> +{
> +	struct exynos_bus *bus = data;
> +
> +	if (spec->np != bus->dev->of_node)
> +		return ERR_PTR(-EINVAL);
> +
> +	return bus->node;
> +}
> +
>  static int exynos_bus_parent_parse_of(struct device_node *np,
>  					struct exynos_bus *bus)
>  {
> @@ -419,6 +463,96 @@ static int exynos_bus_profile_init_passive(struct exynos_bus *bus,
>  	return 0;
>  }
>  
> +static struct icc_node *exynos_bus_icc_get_parent(struct exynos_bus *bus)
> +{
> +	struct device_node *np = bus->dev->of_node;
> +	struct of_phandle_args args;
> +	int num, ret;
> +
> +	num = of_count_phandle_with_args(np, "exynos,interconnect-parent-node",
> +					"#interconnect-cells");
> +	if (num != 1)
> +		return NULL; /* parent nodes are optional */
> +
> +	ret = of_parse_phandle_with_args(np, "exynos,interconnect-parent-node",
> +					"#interconnect-cells", 0, &args);
> +	if (ret < 0)
> +		return ERR_PTR(ret);
> +
> +	of_node_put(args.np);
> +
> +	return of_icc_get_from_provider(&args);
> +}
> +
> +static int exynos_bus_icc_init(struct exynos_bus *bus)
> +{
> +	static DEFINE_IDA(ida);
> +
> +	struct device *dev = bus->dev;
> +	struct icc_provider *provider = &bus->provider;
> +	struct icc_node *node, *parent_node;
> +	int id, ret;
> +
> +	/* Initialize the interconnect provider */
> +	provider->set = exynos_bus_icc_set;
> +	provider->aggregate = icc_std_aggregate;
> +	provider->xlate = exynos_bus_icc_xlate;
> +	provider->dev = dev;
> +	provider->inter_set = true;
> +	provider->data = bus;
> +
> +	ret = icc_provider_add(provider);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = id = ida_alloc(&ida, GFP_KERNEL);
> +	if (ret < 0)
> +		goto err_id;
> +
> +	node = icc_node_create(id);
> +	if (IS_ERR(node)) {
> +		ret = PTR_ERR(node);
> +		goto err_node;
> +	}
> +
> +	bus->node = node;
> +	node->name = dev->of_node->name;
> +	node->data = bus;
> +	icc_node_add(node, provider);
> +
> +	parent_node = exynos_bus_icc_get_parent(bus);
> +	if (IS_ERR(parent_node)) {
> +		ret = PTR_ERR(parent_node);
> +		goto err_parent;
> +	}
> +
> +	if (parent_node) {
> +		ret = icc_link_create(node, parent_node->id);
> +		if (ret < 0)
> +			goto err_parent;
> +	}
> +
> +	ret = dev_pm_qos_add_request(bus->devfreq->dev.parent, &bus->qos_req,
> +					DEV_PM_QOS_MIN_FREQUENCY, 0);
> +	if (ret < 0)
> +		goto err_request;
> +
> +	return 0;
> +
> +err_request:
> +	if (parent_node)
> +		icc_link_destroy(node, parent_node);
> +err_parent:
> +	icc_node_del(node);
> +	icc_node_destroy(id);
> +err_node:
> +	ida_free(&ida, id);
> +err_id:
> +	icc_provider_del(provider);
> +
> +	return ret;
> +}
> +
>  static int exynos_bus_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -468,6 +602,16 @@ static int exynos_bus_probe(struct platform_device *pdev)
>  	if (ret < 0)
>  		goto err;
>  
> +	/*
> +	 * Initialize interconnect provider. A return value of -ENOTSUPP means
> +	 * that CONFIG_INTERCONNECT is disabled.
> +	 */
> +	ret = exynos_bus_icc_init(bus);
> +	if (ret < 0 && ret != -ENOTSUPP) {
> +		dev_err(dev, "failed to initialize the interconnect provider");
> +		goto err;
> +	}
> +
>  	max_state = bus->devfreq->profile->max_state;
>  	min_freq = (bus->devfreq->profile->freq_table[0] / 1000);
>  	max_freq = (bus->devfreq->profile->freq_table[max_state - 1] / 1000);
>