linux-kernel - Re: [PATCH 8/9] PM / Domains: Add support for multi PM domains per device to genpd

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Message-ID: <5a79d3a2-d090-645b-da69-524b7e7a4d90@nvidia.com>
Date:   Tue, 22 May 2018 21:55:15 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Todor Tomov <todor.tomov@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 8/9] PM / Domains: Add support for multi PM domains per
 device to genpd


On 22/05/18 15:47, Ulf Hansson wrote:
> [...]
> 
>>>
>>> +/**
>>> + * genpd_dev_pm_attach_by_id() - Attach a device to one of its PM domain.
>>> + * @dev: Device to attach.
>>> + * @index: The index of the PM domain.
>>> + *
>>> + * Parse device's OF node to find a PM domain specifier at the provided @index.
>>> + * If such is found, allocates a new device and attaches it to retrieved
>>> + * pm_domain ops.
>>> + *
>>> + * Returns the allocated device if successfully attached PM domain, NULL when
>>> + * the device don't need a PM domain or have a single PM domain, else PTR_ERR()
>>> + * in case of failures. Note that if a power-domain exists for the device, but
>>> + * cannot be found or turned on, then return PTR_ERR(-EPROBE_DEFER) to ensure
>>> + * that the device is not probed and to re-try again later.
>>> + */
>>> +struct device *genpd_dev_pm_attach_by_id(struct device *dev,
>>> +                                      unsigned int index)
>>> +{
>>> +     struct device *genpd_dev;
>>> +     int num_domains;
>>> +     int ret;
>>> +
>>> +     if (!dev->of_node)
>>> +             return NULL;
>>> +
>>> +     /* Deal only with devices using multiple PM domains. */
>>> +     num_domains = of_count_phandle_with_args(dev->of_node, "power-domains",
>>> +                                              "#power-domain-cells");
>>> +     if (num_domains < 2 || index >= num_domains)
>>> +             return NULL;
>>> +
>>> +     /* Allocate and register device on the genpd bus. */
>>> +     genpd_dev = kzalloc(sizeof(*genpd_dev), GFP_KERNEL);
>>> +     if (!genpd_dev)
>>> +             return ERR_PTR(-ENOMEM);
>>> +
>>> +     dev_set_name(genpd_dev, "genpd:%u:%s", index, dev_name(dev));
>>> +     genpd_dev->bus = &genpd_bus_type;
>>> +     genpd_dev->release = genpd_release_dev;
>>> +
>>> +     ret = device_register(genpd_dev);
>>> +     if (ret) {
>>> +             kfree(genpd_dev);
>>> +             return ERR_PTR(ret);
>>> +     }
>>> +
>>> +     /* Try to attach the device to the PM domain at the specified index. */
>>> +     ret = __genpd_dev_pm_attach(genpd_dev, dev->of_node, index);
>>> +     if (ret < 1) {
>>> +             device_unregister(genpd_dev);
>>> +             return ret ? ERR_PTR(ret) : NULL;
>>> +     }
>>> +
>>> +     pm_runtime_set_active(genpd_dev);
>>> +     pm_runtime_enable(genpd_dev);
>>> +
>>> +     return genpd_dev;
>>> +}
>>> +EXPORT_SYMBOL_GPL(genpd_dev_pm_attach_by_id);
>>
>> Thanks for sending this. Believe it or not this has still been on my to-do list
>> and so we definitely need a solution for Tegra.
>>
>> Looking at the above it appears that additional power-domains exposed as devices
>> to the client device. So I assume that this means that the drivers for devices
>> with multiple power-domains will need to call RPM APIs for each of these
>> additional power-domains. Is that correct?
> 
> They can, but should not!
> 
> Instead, the driver shall use device_link_add() and device_link_del(),
> dynamically, depending on what PM domain that their original device
> needs for the current running use case.
> 
> In that way, they keep existing runtime PM deployment, operating on
> its original device.

OK, sounds good. Any reason why the linking cannot be handled by the 
above API? Is there a use-case where you would not want it linked?

Thanks
Jon

-- 
nvpublic