Re: [PATCH 00/18] ARM/ARM64: Support hierarchical CPU arrangement for PSCI

From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	"Raju P . L . S . S . S . N" <rplsssn@codeaurora.org>,
	Amit Kucheria <amit.kucheria@linaro.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Niklas Cassel <niklas.cassel@linaro.org>,
	Tony Lindgren <tony@atomide.com>,
	Kevin Hilman <khilman@kernel.org>,
	Lina Iyer <ilina@codeaurora.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Souvik Chakravarty <souvik.chakravarty@arm.com>,
	Linux PM <linux-pm@vger.kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/18] ARM/ARM64: Support hierarchical CPU arrangement for PSCI
Date: Fri, 7 Jun 2019 12:34:07 -0700	[thread overview]
Message-ID: <20190607193407.GB24059@builder> (raw)
In-Reply-To: <20190607154210.GJ15577@e107155-lin>

On Fri 07 Jun 08:42 PDT 2019, Sudeep Holla wrote:

> On Tue, May 14, 2019 at 10:58:04AM +0200, Ulf Hansson wrote:
> > On Tue, 14 May 2019 at 10:08, Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Mon, May 13, 2019 at 9:23 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > >
> > > > This series enables support for hierarchical CPU arrangement, managed by PSCI
> > > > for ARM/ARM64. It's based on using the generic PM domain (genpd), which
> > > > recently was extended to manage devices belonging to CPUs.
> > >
> > > ACK for the patches touching cpuidle in this series (from the
> > > framework perspective), but I'm assuming it to be taken care of by
> > > ARM/ARM64 maintainers.
> >
> > Thanks for the ack! Yes, this is for PSCI/ARM maintainers.
> >
> > BTW, apologize for sending this in the merge window, but wanted to
> > take the opportunity for people to have a look before OSPM Pisa next
> > week.
> >
> 
> I will start looking at this series. But I would request PSCI/other
> maintainers to wait until we see some comparison data before we merge.

What comparison are you asking for here? Do you want to see the
improvement this series gives or are you hoping to compare it with some
other mechanism?

> If they are fine to merge w/o that, I am fine. As of now we have just
> 1-2 platforms to test(that too not so simple to get started) and the
> long term support for them are questionable.

Why is the support for these platforms questionable? People are actively
working on these platforms and the feature set constantly improving.

> Also with SDM845 supporting PC, we have excellent opportunity to
> compare and conclude the results found.

That's correct, ATF exists for SDM845. But with the standard choice of
firmware you will get OSI and I don't know of a board out there where
you can switch between them and do a apple to apple comparison.

Devices such as RB3 (96boards SDM845), Pixel3 and the Windows laptops
are all OSI only.

So landing this support is not a question of PC or OSI being the better
choice, it's a question of do we want to be able to enter these lower
power states - with the upstream kernel - on any past, present or future
Qualcomm devices.

Regards,
Bjorn