linux-kernel - Re: [PATCH 0/2] clk: renesas: rzg2l: Disable unused clocks after resume

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Message-ID: <CAMuHMdXNnGg0rEcM1hvvjBUJXFFAx4oiX=qVb3nKfmd4YBxhGw@mail.gmail.com>
Date: Mon, 1 Sep 2025 11:46:34 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Brian Masney <bmasney@...hat.com>
Cc: claudiu beznea <claudiu.beznea@...on.dev>, mturquette@...libre.com, sboyd@...nel.org, 
	geert+renesas@...der.be, linux@...linux.org.uk, 
	linux-renesas-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 0/2] clk: renesas: rzg2l: Disable unused clocks after resume

Hi Brian,

On Tue, 26 Aug 2025 at 13:52, Brian Masney <bmasney@...hat.com> wrote:
> On Tue, Aug 26, 2025 at 02:01:56PM +0300, claudiu beznea wrote:
> > On 8/25/25 20:05, Brian Masney wrote:
> > > On Thu, Aug 21, 2025 at 11:03:30AM +0300, Claudiu wrote:
> > > > From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> > > > This series disables clocks that remain unused after resume.
> > > > This is necessary when the resume process is done with the help of the
> > > > bootloader, as the bootloader enables various clocks when returning from
> > > > resume.
> > > >
> > > > On the RZ/G3S SoC (where this series was tested), the bootloader enables
> > > > the SDHI clocks (for all SDHI modules, of which 2 are used by Linux and
> > > > 1 is unused) and the clocks for a serial IP (unused by Linux).
> > > >
> > > > Testing was done on the RZ/G3S SMARC Carrier II board.
> > >
> > > Do you think that other boards would also benefit from this change? If
> > > so, what do you think about putting the call to register_pm_notifier()
> > > inside an __init block in clk.c so that this same change doesn't have to
> > > be implemented across various clk drivers?
> >
> > Yes, that was my other approach I was thinking about. I wanted to see how
> > other people consider this version.
> >
> > > Alternatively, if this is board specific, could this be fixed in the
> > > boot loader so that the clock that's not used by Linus is properly shut
> > > down on resume?
> >
> > As a result of your request I did some more investigations on my side, I can
> > say that, yes, in theory that could be also handled by bootloader.
> >
> > I can drop this and try to do it in bootloader, if any. Please let me know
> > if you still consider this (or the variant that implements it in a generic
> > way) necessary.
>
> Personally I would go the route of fixing this in the bootloader for
> this particular platform.
>
> If this issue affects other platforms, particularly across multiple
> SoC vendors, then I think it would be worthwhile to have a discussion
> about adding this functionality to the clk core.

How would the bootloader know which clocks are not used by Linux?
And why to offload this to the bootloader for resume, but not for boot?

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