linux-kernel - Re: [PATCH 07/18] drivers: firmware: psci: Prepare to use OS initiated suspend mode

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Date:   Mon, 10 Jun 2019 11:42:53 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Raju P . L . S . S . S . N" <rplsssn@...eaurora.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Tony Lindgren <tony@...mide.com>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Souvik Chakravarty <souvik.chakravarty@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lina Iyer <lina.iyer@...aro.org>
Subject: Re: [PATCH 07/18] drivers: firmware: psci: Prepare to use OS
 initiated suspend mode

On Mon, Jun 10, 2019 at 12:21:10PM +0200, Ulf Hansson wrote:
> On Fri, 7 Jun 2019 at 17:17, Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Mon, May 13, 2019 at 09:22:49PM +0200, Ulf Hansson wrote:
> > > The per CPU variable psci_power_state, contains an array of fixed values,
> > > which reflects the corresponding arm,psci-suspend-param parsed from DT, for
> > > each of the available CPU idle states.
> > >
> > > This isn't sufficient when using the hierarchical CPU topology in DT in
> > > combination with having PSCI OS initiated (OSI) mode enabled. More
> > > precisely, in OSI mode, Linux is responsible of telling the PSCI FW what
> > > idle state the cluster (a group of CPUs) should enter, while in PSCI
> > > Platform Coordinated (PC) mode, each CPU independently votes for an idle
> > > state of the cluster.
> > >
> > > For this reason, let's introduce an additional per CPU variable called
> > > domain_state and implement two helper functions to read/write its values.
> > > Following patches, which implements PM domain support for PSCI, will use
> > > the domain_state variable and set it to corresponding bits that represents
> > > the selected idle state for the cluster.
> > >
> > > Finally, in psci_cpu_suspend_enter() and psci_suspend_finisher(), let's
> > > take into account the values in the domain_state, as to get the complete
> > > suspend parameter.
> > >
> >
> > I understand it was split to ease review, but this patch also does
> > nothing as domain_state = 0 always. I was trying hard to find where it's
> > set, but I assume it will be done in later patches. Again may be this
> > can be squashed into the first caller of psci_set_domain_state
> 
> You have a point, but I am worried that it would look like this series
> is solely needed to support OSI mode. This is not the case. Let me
> explain.
> 
> Having $subject patch separate shows the specific changes needed to
> support OSI mode. The first caller of psci_set_domain_state() is added
> in patch9, however, patch9 is useful no matter of OSI or PC mode.
> 
> Moreover, if I squash $subject patch with patch9, I would have to
> squash also the subsequent patch (patch8), as it depends on $subject
> patch.
> 
> So, to conclude, are you happy with this as is or do you want me to
> squash the patches?
> 

Yes I am fine either way. As I put the comments in the same flow as I
did review, I thought it's worth mentioning if someone else get similar
thoughts. I am fine if you prefer to keep it the same way unless someone
else raise the same point.

--
Regards,
Sudeep