linux-kernel - Re: [PATCH v7 4/7] reset: rzg2l-usbphy-ctrl: Add support for USB PWRRDY

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Message-ID: <CAMuHMdVQ_Eabhz0=FRB28BqdidQDpjdBOGq6+9yR6pioNfA_Lg@mail.gmail.com>
Date: Wed, 15 Oct 2025 10:51:15 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Philipp Zabel <p.zabel@...gutronix.de>
Cc: Claudiu Beznea <claudiu.beznea@...on.dev>, vkoul@...nel.org, kishon@...nel.org, 
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	magnus.damm@...il.com, yoshihiro.shimoda.uh@...esas.com, 
	biju.das.jz@...renesas.com, linux-phy@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: Re: [PATCH v7 4/7] reset: rzg2l-usbphy-ctrl: Add support for USB PWRRDY

Hi Philipp,

On Tue, 14 Oct 2025 at 18:42, Philipp Zabel <p.zabel@...gutronix.de> wrote:
> On Di, 2025-10-14 at 11:36 +0300, Claudiu Beznea wrote:
> > On 10/13/25 17:57, Philipp Zabel wrote:
> > > Is the issue that you need the PWRRDY signal to be (de)asserted
> > > independently from the CPG power domain enable/disable?
> >
> > Yes. I need to de-assert it before clocks, MSTOP on probe/resume and assert
> > it back after clocks, MSTOP, on remove/suspend.
> >
> > > (Why?)
> >
> > Due to hardware constraints. This is how Renesas HW team recommended.
>
> I still haven't understood this part. Isn't CPG the power domain
> enabled "before clocks, MSTOP on probe resume" and disabled "after
> clocks, MSTOP, on remove/suspend"? So PWRRDY could be toggled from
> genpd notifications. If it needs to be (de)asserted independently,
> wouldn't that mean the genpd notifier approach can not be used?
> The notifiers are called from genpd_power_on/off(), after all.

Please let me chime in to clarify...

The CPG is not a power domain in the sense of a power area that can
be powered on or off.
The CPG is a clock domain in the Linux PM Domain abstraction, more
specifically an always-on power domain that contains devices that are
all power-managed similarly, through their module clock(s).
Hence the CPG PM Domain itself cannot be powered on or off (through
the generic_pm_domain.power_o{ff,n}() callbacks), but the individual
devices that are part of it can be started/stopped (through the
generic_pm_domain.dev_ops.{start,stop}() callbacks).

I hope this helps.

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