linux-kernel - Re: [PATCH] soc: rockchip: power-domain: remove PM clocks

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Date:   Thu, 1 Mar 2018 09:33:22 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     JeffyChen <jeffy.chen@...k-chips.com>
Cc:     Tomasz Figa <tfiga@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Heiko Stuebner <heiko@...ech.de>,
        Caesar Wang <wxt@...k-chips.com>,
        Elaine Zhang <zhangqing@...k-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH] soc: rockchip: power-domain: remove PM clocks

Hi Jeffy,

On Thu, Mar 1, 2018 at 4:40 AM, JeffyChen <jeffy.chen@...k-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@...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