Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider which controls

From: Linus Walleij <linus.walleij@linaro.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Max Krummenacher <max.oss.09@gmail.com>,
	Max Krummenacher <max.krummenacher@toradex.com>,
	Linux PM list <linux-pm@vger.kernel.org>,
	Francesco Dolcini <francesco.dolcini@toradex.com>,
	Mark Brown <broonie@kernel.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Kevin Hilman <khilman@kernel.org>,
	Andrejs Cainikovs <andrejs.cainikovs@toradex.com>,
	Biju Das <biju.das.jz@bp.renesas.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Fabio Estevam <festevam@gmail.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Marcel Ziswiler <marcel.ziswiler@toradex.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Rob Herring <robh+dt@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
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	Will Deacon <will@kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
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Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider which controls
Date: Mon, 18 Jul 2022 11:49:11 +0200	[thread overview]
Message-ID: <CACRpkdb4qZSUNhEjRRJi=5H-GvBi_h-0BAfDHJct5SjLKZSc3g@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFrEYCx3L94gz27Pk_=HdwA4GNGE9Lvz+HGUW0P7Qt-mBw@mail.gmail.com>

On Wed, Jul 13, 2022 at 1:44 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:

> > > IIRC this led to problems because we had to invent "atomic regulators"
> > > because regulators use kernel abstractions that assume slowpath
> > > (process context) and power domains does not, i.e. they execute in
> > > fastpath, such as an interrupt handler.
>
> This isn't entirely correct. The callbacks of a genpd, *may* execute
> in atomic context, but that depends on whether the GENPD_FLAG_IRQ_SAFE
> is set for it or not.
>
> Similar to what we have for runtime PM callbacks, with pm_runtime_irq_safe().

Aha I stand corrected!

> > > The atomic regulator was a subset of regulator that only handled
> > > regulators that would result in something like an atomic register write.
> > >
> > > In the end it was not worth trying to upstream this approach, and
> > > as I remember it, Ulf Hansson intended to let the power domains poke
> > > these registers directly, which was easier. (It's on Ulfs TODO list to
> > > actually implement this, hehe.)
>
> Yep, unfortunately I never got to the point. However, poking the
> registers directly from the genpd provider's on/off callbacks has
> never been my plan.
>
> Instead I would rather expect us to call into a Ux500 specific
> interface for the prcmu FW. Simply because it's not really a regulator
> and must not be modelled like it. Instead it is a voltage/frequency
> domain that is managed behind a FW interface.

We should take a stab at this, PostmarketOS just added support
for three more U8500 phones so they support all the Samsung models
and we have actual users of these systems. I think this would save
them quite a lot of power. Also I use these targets for a lot of
misc testing (like Kasan etc).

Yours,
Linus Walleij