linux-kernel - Re: [PATCH v8 07/34] clk: tegra: Support runtime PM and power domain

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Message-ID: <ad99db08-4696-1636-5829-5260f93dc681@gmail.com>
Date:   Wed, 18 Aug 2021 20:11:03 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v8 07/34] clk: tegra: Support runtime PM and power domain

18.08.2021 19:42, Thierry Reding пишет:
> On Wed, Aug 18, 2021 at 06:05:21PM +0300, Dmitry Osipenko wrote:
>> 18.08.2021 17:07, Thierry Reding пишет:
>>> On Tue, Aug 17, 2021 at 04:27:27AM +0300, Dmitry Osipenko wrote:
>>> [...]
>>>> +struct clk *tegra_clk_register(struct clk_hw *hw)
>>>> +{
>>>> +	struct platform_device *pdev;
>>>> +	struct device *dev = NULL;
>>>> +	struct device_node *np;
>>>> +	const char *dev_name;
>>>> +
>>>> +	np = tegra_clk_get_of_node(hw);
>>>> +
>>>> +	if (!of_device_is_available(np))
>>>> +		goto put_node;
>>>> +
>>>> +	dev_name = kasprintf(GFP_KERNEL, "tegra_clk_%s", hw->init->name);
>>>> +	if (!dev_name)
>>>> +		goto put_node;
>>>> +
>>>> +	pdev = of_platform_device_create(np, dev_name, NULL);
>>>> +	if (!pdev) {
>>>> +		pr_err("%s: failed to create device for %pOF\n", __func__, np);
>>>> +		kfree(dev_name);
>>>> +		goto put_node;
>>>> +	}
>>>> +
>>>> +	dev = &pdev->dev;
>>>> +	pm_runtime_enable(dev);
>>>> +put_node:
>>>> +	of_node_put(np);
>>>> +
>>>> +	return clk_register(dev, hw);
>>>> +}
>>>
>>> This looks wrong. Why do we need struct platform_device objects for each
>>> of these clocks? That's going to be a massive amount of platform devices
>>> and they will completely mess up sysfs.
>>
>> RPM works with a device. It's not a massive amount of devices, it's one
>> device for T20 and four devices for T30.
> 
> I'm still not sure I understand why we need to call RPM functions on a
> clock. And even if they are few, it seems wrong to make these platform
> devices.

Before clock is enabled, we need to raise core voltage. After clock is
disabled, the voltage should be dropped. CCF+RPM takes care of handling
this for us.

> Perhaps they can be simple struct device:s instead? Ideally they would
> also be parented to the CAR so that they appear in the right place in
> the sysfs hierarchy.

Could you please clarify what do you mean by 'simple struct device:s'?
These clock devices should be OF devices with a of_node and etc,
otherwise we can't use OPP framework.

We don't have driver for CAR to bind. I guess we could try to add a
'dummy' CAR driver that will create sub-devices for the rpm-clocks, is
this what you're wanting?