linux-kernel - Re: [PATCH v5 5/6] rockchip/soc/drivers: Add DTPM description for rk3399

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Date:   Tue, 4 Jan 2022 10:29:09 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh@...nel.org>, rjw@...ysocki.net,
        lukasz.luba@....com, heiko@...ech.de, arnd@...aro.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "moderated list:ARM/Rockchip SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v5 5/6] rockchip/soc/drivers: Add DTPM description for rk3399

On Fri, Dec 31, 2021 at 2:58 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On Sat, 18 Dec 2021 at 14:00, Daniel Lezcano <daniel.lezcano@...aro.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@...aro.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@...aro.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? If not, perhaps no new
properties are needed, and power-domains/#power-domain-cells can be
used as is?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds