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Subject: Re: [RFC PATCH v5 2/6] interconnect: Add generic interconnect driver
 for Exynos SoCs
To:     Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc:     cw00.choi@samsung.com, krzk@kernel.org, a.swigon@samsung.com,
        myungjoo.ham@samsung.com, inki.dae@samsung.com,
        sw0312.kim@samsung.com, b.zolnierkie@samsung.com,
        m.szyprowski@samsung.com, linux-kernel@vger.kernel.org,
        linux-samsung-soc@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org
References: <20200529163200.18031-1-s.nawrocki@samsung.com>
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 <1c277836-efdf-f7b8-aa62-7369349fe21f@samsung.com>
From:   Georgi Djakov <georgi.djakov@linaro.org>
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Message-ID: <d3a45a91-d223-d3a2-a9fb-adadca98c80d@linaro.org>
Date:   Thu, 2 Jul 2020 15:33:35 +0300
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In-Reply-To: <1c277836-efdf-f7b8-aa62-7369349fe21f@samsung.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Sylwester,

On 7/2/20 15:01, Sylwester Nawrocki wrote:
> Hi Georgi,
> 
> On 01.07.2020 14:50, Georgi Djakov wrote:
>> Thanks for the patch and apologies for the delayed reply.
> 
> Thanks, no problem. It's actually just in time as I put that patchset
> aside for a while and was just about to post an update.
>  
>> On 5/29/20 19:31, Sylwester Nawrocki wrote:
>>> 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.
>>>
>>> Signed-off-by: Artur Świgoń <a.swigon@samsung.com>
>>> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
> 
>>> +static struct icc_node *exynos_icc_get_parent(struct device_node *np)
>>> +{
>>> +	struct of_phandle_args args;
>>> +	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);
>>> +
>>> +	of_node_put(args.np);
>>> +
>>> +	return of_icc_get_from_provider(&args);
>>> +}
>>> +
>>> +
>>
>> Nit: multiple blank lines
> 
> Fixed.
> 
>> [..]
>>> +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))
>>
>> Nit: !IS_ERR_OR_NULL?
> 
> It was left on purpose that way but I changed it now to IS_ERR_OR_NULL.

Well, i have no strong opinion on that, it's up to you.

>>> +		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);
>>
>> Nit: Maybe it would be better to move this after the node is created. The
>> idea is to create the nodes first and add the provider when the topology is
>> populated. It's fine either way here, but i am planning to change this in
>> some of the existing provider drivers.
> 
> OK, it makes the clean up path a bit less straightforward. And still we need 
> to register the provider before calling icc_node_add().
> I made a change as below.
> 
> --------------8<------------------
> @@ -124,14 +123,14 @@ static int exynos_generic_icc_probe(struct platform_device *pdev)
>  	provider->inter_set = true;
>  	provider->data = priv;
>  
> +	icc_node = icc_node_create(pdev->id);
> +	if (IS_ERR(icc_node))
> +		return PTR_ERR(icc_node);
> +
>  	ret = icc_provider_add(provider);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		icc_node_destroy(icc_node->id);
>  		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;
> @@ -171,9 +170,7 @@ static int exynos_generic_icc_probe(struct platform_device *pdev)
>  		icc_link_destroy(icc_node, icc_parent_node);
>  err_node_del:
>  	icc_nodes_remove(provider);
> -err_prov_del:
>  	icc_provider_del(provider);
> -
>  	return ret;
>  }
> --------------8<------------------

Actually i need to post some patches first, so maybe keep it as is for now and
we will update it afterwards. Sorry for the confusion.

> 
> 
>>> +	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 = bus_dev->of_node->name;
>>> +	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;
>>> +}
> 
>> All looks good to me, but it seems that the patch-set is not on
>> Rob's radar currently, so please re-send and CC the DT mailing list.
> 
> Thanks, indeed I missed some mailing list when posting. I will make sure
> Rob and DT ML list is on Cc, especially that I have added new "bus-width" 
> property in v6.

Ok, good. I have been thinking about bus-width and we might want to make it
even a generic DT property if there are multiple platforms which want to
use it - maybe if the bus-width is the same across the whole interconnect
provider. But as most of the existing drivers have different bus-widths, i
haven't done it yet, but let's see and start a discussion.

Thanks,
Georgi