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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 1 Mar 2018 09:33:22 +0100
Message-ID: <CAMuHMdU9PFAXwo+1Z7Baw1fanst9yFKZ3ohoSTiQiMKTaYMVVw@mail.gmail.com>
Subject: Re: [PATCH] soc: rockchip: power-domain: remove PM clocks
To:     JeffyChen <jeffy.chen@rock-chips.com>
Cc:     Tomasz Figa <tfiga@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Caesar Wang <wxt@rock-chips.com>,
        Elaine Zhang <zhangqing@rock-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
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Hi Jeffy,

On Thu, Mar 1, 2018 at 4:40 AM, JeffyChen <jeffy.chen@rock-chips.com> wrote:
> if i'm reading the code right, the PM clk means:
> 1/ the clocks which would be enabled while power on
> 2/ these clocks are optional, it's ok if anything wrong with them
> 3/ controlled by pm_domain(or USE_PM_CLK_RUNTIME_OPS & pm_clk_add_notifier)
>
> and currently we're adding all clocks of the attached device as PM clk in
> rockchip PM domain driver, which seems wrong. because we might have these
> kinds of clocks:
> 1/ critical, should block power on if anything wrong with it(failed to get/
> prepare/ enable)
> 2/ optional, could ignore it if anything wrong
> 3/ only required in some special cases, for example register r/w, and
> doesn't need to stay enabled while power on
>
> so maybe we can:
> 1/ let the device(dts) or driver decide which clock is PM clk, and add it
> using *pm_clk_add* APIs (even of_pm_clk_add_clks() if all clocks are pm clk)
>
> 2/ add support for critical PM clk, which would return error to the driver
> if anything wrong
>
> 3/ make sure PM clk always be controlled(otherwise it might be unexpected
> disabled by other clocks under the same clk parent?):
>  a) make sure Runtime PM is always enabled. and as discussed, we can select
> PM in ARCH_ROCKCHIP

On Renesas SoCs, we only add the device's module clock with pm_clk_add().
Drivers that don't care about properties of the module clock just call
pm_runtime_*(). That way the same driver works on different SoCs using
the same device, with and without power and/or clock domains.

Drivers that care about properties of the module clock (mainly frequency)
can still use the clk_*() API for that. Other (optional) clocks must be
handled by the device driver itself.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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