linux-kernel - Re: [PATCH 05/12] PCI: aardvark: add suspend to RAM support

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Date:   Tue, 18 Dec 2018 11:54:43 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Stephen Boyd <sboyd@...nel.org>, sudeep.holla@....com,
        Gregory Clement <gregory.clement@...tlin.com>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>
Subject: Re: [PATCH 05/12] PCI: aardvark: add suspend to RAM support

On Monday, December 17, 2018 3:54:26 PM CET Miquel Raynal wrote:
> Hi Rafael,
> 
> "Rafael J. Wysocki" <rjw@...ysocki.net> wrote on Thu, 13 Dec 2018
> 22:50:51 +0100:
> 
> > On Thursday, December 13, 2018 3:30:00 PM CET Miquel Raynal wrote:
> > > Hi Lorenzo,
> > >   
> > > > > If that's really the case, then I can see how one device and it's
> > > > > children are suspended and the irq for it is disabled but the providing
> > > > > devices (clk, regulator, bus controller, etc.) are still fully active
> > > > > and not suspended but in fact completely usable and able to service
> > > > > interrupts. If that all makes sense, then I would answer the question
> > > > > with a definitive "yes it's all fine" because the clk consumer could be
> > > > > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > > > > even started suspending yet when clk_disable_unprepare() is called.    
> > > > 
> > > > That's a very good summary and address my concern, I still question this
> > > > patch correctness (and many others that carry out clk operations in S2R
> > > > NOIRQ phase), they may work but do not tell me they are rock solid given
> > > > your accurate summary above.  
> > > 
> > > I understand your concern but I don't see any alternative right now
> > > and a deep rework of the PM core to respect such dependency is not
> > > something that can be done in a reasonable amount of time.  
> > 
> > Maybe you don't need to rework anything. :-)
> > 
> > Have you considered using device links?
> 
> Absolutely, yes :) I am actively working on it in parallel, you can
> check the third version there [1]. Stephen Boyd has a slightly
> different idea of how it should be done, I will propose a v4 this week,
> I can add you in copy if you are interested!
> 
> Anyway, there is one thing that is still missing:
> * Let's have device A that requests clock B
> * With the device link series, A is linked (as a child) to B.
> * A suspend/resume hooks handle things in the NOIRQ phase.

Why do you need them to run in the "noirq" phase in the first place?

> * B suspend/resume hooks handle things in the default phase.
> 
> What I expected during a suspend:
> 1/ ->suspend_noirq(device A)
> 2/ ->suspend(clock B)

This expectation is not in agreement with the documented suspend code flow,
however.

Each phase of it is carried out for *all* devices completely before getting
to the next phase, "prepare" first, then "suspend", "suspend_late" and
"suspend_noirq", in this order.

> Unfortunately, device links do not seem to enforce any priority between
> phases (default/late/noirq) and what happens is:
> 1/ ->suspend(B)
> 2/ ->suspend_noirq(A)
> Which has no sense in my case. Hence, I had to request the clock
> suspend/resume callbacks to be upgraded to the NOIRQ phase as well (I
> don't have a better solution for now). This is still under discussion
> in a thread you have been recently added to by Bjorn, see [2].
> 
> So when I told you I was not confident in "reworking the PM core to
> respect such dependency", this is what I was referring to. I am
> definitely ready to help, but I don't feel I can do it alone.
> 
> [1] https://www.spinics.net/lists/linux-clk/msg32824.html
> [2] https://marc.info/?l=linux-pm&m=154465198510735&w=2

The rework you seem to be talking about is not possible, I'm afraid.