Subject: Re: [PATCH v5 5/6] rockchip/soc/drivers: Add DTPM description for
 rk3399
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Rob Herring <robh@kernel.org>, rjw@rjwysocki.net,
        lukasz.luba@arm.com, heiko@sntech.de, arnd@linaro.org,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        "moderated list:ARM/Rockchip SoC support" 
        <linux-arm-kernel@lists.infradead.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@lists.infradead.org>
References: <20211218130014.4037640-1-daniel.lezcano@linaro.org>
 <20211218130014.4037640-6-daniel.lezcano@linaro.org>
 <CAPDyKFqWUJTKte3dM=7xG6EtKR8i9neCCNYFs7Jf1J34TezUEQ@mail.gmail.com>
 <CAMuHMdXzs9WMksQAJXdYaQndsqK3CnQZTGYw=TSFVrDEdX8PCA@mail.gmail.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <08787cb7-439e-74a4-f268-6c8de0d60a30@linaro.org>
Date:   Wed, 5 Jan 2022 10:21:58 +0100
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Hi Geert,

thanks for your feedback

On 04/01/2022 10:29, Geert Uytterhoeven wrote:
> On Fri, Dec 31, 2021 at 2:58 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On Sat, 18 Dec 2021 at 14:00, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>>> The DTPM framework does support now the hierarchy description.
>>>
>>> The platform specific code can call the hierarchy creation function
>>> with an array of struct dtpm_node pointing to their parent.
>>>
>>> This patch provides a description of the big and Little CPUs and the
>>> GPU and tie them together under a virtual package name. Only rk3399 is
>>> described now.
>>>
>>> The description could be extended in the future with the memory
>>> controller with devfreq if it has the energy information.
>>>
>>> The hierarchy uses the GPU devfreq with the panfrost driver, and this
>>> one could be loaded as a module. If the hierarchy is created before
>>> the panfrost driver is loaded, it will fail. For this reason the
>>> Kconfig option depends on the panfrost Kconfig's option. If this one
>>> is compiled as a module, automatically the dtpm hierarchy code will be
>>> a module also. Module loading ordering will fix this chicken-egg
>>> problem.
>>>
>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> 
>>> --- /dev/null
>>> +++ b/drivers/soc/rockchip/dtpm.c
>>> @@ -0,0 +1,56 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * Copyright 2021 Linaro Limited
>>> + *
>>> + * Author: Daniel Lezcano <daniel.lezcano@linaro.org>
>>> + *
>>> + * DTPM hierarchy description
>>> + */
>>> +#include <linux/dtpm.h>
>>> +#include <linux/module.h>
>>> +#include <linux/of.h>
>>> +#include <linux/platform_device.h>
>>> +
>>> +static struct dtpm_node __initdata rk3399_hierarchy[] = {
>>> +       [0]{ .name = "rk3399" },
>>> +       [1]{ .name = "package",
>>> +            .parent = &rk3399_hierarchy[0] },
>>> +       [2]{ .name = "/cpus/cpu@0",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [3]{ .name = "/cpus/cpu@1",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [4]{ .name = "/cpus/cpu@2",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [5]{ .name = "/cpus/cpu@3",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [6]{ .name = "/cpus/cpu@100",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [7]{ .name = "/cpus/cpu@101",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [8]{ .name = "rockchip,rk3399-mali",
>>> +            .type = DTPM_NODE_DT,
>>> +            .parent = &rk3399_hierarchy[1] },
>>> +       [9]{ },
>>> +};
>>
>> I will not object to this, as in the end this seems like what we need
>> to do, unless we can describe things through generic DT bindings for
>> DTPM. Right?
>>
>> Although, if the above is correct, I need to stress that I am kind of
>> worried that this doesn't really scale. We would need to copy lots of
>> information from the DTS files into platform specific c-files, to be
>> able to describe the DTPM hierarchy.
> 
> The description in rk3399_hierarchy[] looks fairly similar to a
> power-domains hierarchy, like we have in e.g. the various
> drivers/soc/renesas/r8*-sysc.c files.  One big difference is that the
> latter do not hardcode the node paths in the driver, but use power
> domain indices, referenced from DT in power-domains properties.
> 
> Perhaps a similar approach can be used for DTPM?
> Does DTPM differ a lot from PM Domains? 

Yes they differ. A DTPM node is a powerzone, a place where we can get
and set the power.

That is the reason why initially a separate binding was proposed.

> If not, perhaps no new
> properties are needed, and power-domains/#power-domain-cells can be
> used as is?


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