linux-kernel - Re: [PATCH v3 00/15] Bring suspend to RAM support to PCIe Aardvark driver

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Date:   Fri, 25 Jan 2019 13:57:57 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     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 v3 00/15] Bring suspend to RAM support to PCIe Aardvark
 driver

Hi Lorenzo,

Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote on Fri, 25 Jan 2019
12:40:11 +0000:

> On Fri, Jan 25, 2019 at 11:05:30AM +0100, Miquel Raynal wrote:
> > Hi Lorenzo,
> > 
> > Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote on Wed, 23 Jan 2019
> > 17:05:09 +0000:
> >   
> > > On Tue, Jan 08, 2019 at 05:24:25PM +0100, Miquel Raynal wrote:  
> > > > Hello,
> > > > 
> > > > As part of an effort to bring suspend to RAM support to Armada 3700
> > > > SoCs (main target: ESPRESSObin), this series handles the work around
> > > > the PCIe IP.
> > > > 
> > > > First, more configuration is done in the 'setup' helper as inspired
> > > > from the U-Boot driver. This is needed to entirely initialize the IP
> > > > during future resume operation (patch 1).
> > > > 
> > > > Then, reset GPIO, PHY and clock support are introduced (patch 2-4). As
> > > > current device trees do not provide the corresponding properties, not
> > > > finding one of these properties is not an error and just produces a
> > > > warning. However, if the property is present, an error during PHY
> > > > initialization will fail the probe of the driver.
> > > > 
> > > > Note: To be sure the clock will be resumed before this driver, a first
> > > > series adding links between clocks and consumers has been submitted,
> > > > see [1]. Anyway, having the clock series applied first is not needed.    
> > > 
> > > I do not understand what this means, in particular in relation
> > > to the blocking clock calls in the suspend/resume NOIRQ hooks.  
> > 
> > I am not sure to understand your question.
> > 
> > As there are multiple points in this sentence I will detail each of
> > them so please comment on the one which is bothering you:
> > * I am working in parallel on a series adding device links to the clock
> >   framework. This way when a driver consumes a clock, the clock
> >   provider driver will be resumed first.
> > * If the clock series I am talking about is applied after this one,
> >   there is no build issue. Of course suspending the platform may
> >   not work but this is a new feature so nothing will be broken.  
> 
> Suspend to RAM will be broken if the clock is suspended and no
> notification will happen in the NOIRQ phase, it is a new-broken-feature.
>
> 
> > * Device links do not enforce any priority if the suspend/resume phase
> >   between two drivers is not the same. The PCIe driver suspends in the
> >   NOIRQ phase. If we want the clock driver to suspend *after* PCIe, its
> >   suspend/resume callbacks must be promoted to the NOIRQ phase as well
> >   (and this is part of another series). As of today there is
> >   no alternative.  
> 
> I will merge this series when it works, I have no evidence that it does
> given what you are writing above, if the series you mention are
> *necessary* for suspend-to-RAM to work they ought to be merged first.

I am working actively to bring A3700 SoC suspend to RAM support almost
from scratch. 

As of today I have contributed 65 patches spread in 8 series for the
PHY, clk, PCIe, SATA, USB, pinctrl and net subsystems. Some of them
have been merged, but the vast majority has not, yet.

I mentioned this run-time dependency because it exists for people who
would like to test just the PCIe IP. But S2RAM on A3700 will be a
new-broken-feature until all patches are merged. While there is
still one missing, the feature is broken. If everybody waits for
the other patches to be merged first, it is gonna be a long process :)

However, if you want to wait for the clock core series to be applied
first I respect this choice and I will update you when it will be the
case.


Thanks,
Miquèl