From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>, sboyd@kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>, Andrew Lunn <andrew@lunn.ch>,
Jason Cooper <jason@lakedaemon.net>,
devicetree@vger.kernel.org,
Antoine Tenart <antoine.tenart@bootlin.com>,
linux-pci@vger.kernel.org,
Gregory Clement <gregory.clement@bootlin.com>,
Miquel Raynal <miquel.raynal@bootlin.com>,
linux-kernel@vger.kernel.org,
Maxime Chevallier <maxime.chevallier@bootlin.com>,
Nadav Haklai <nadavh@marvell.com>,
Rob Herring <robh+dt@kernel.org>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
sudeep.holla@arm.com, Bjorn Helgaas <bhelgaas@google.com>,
linux-arm-kernel@lists.infradead.org,
Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Subject: Re: [PATCH 05/12] PCI: aardvark: add suspend to RAM support
Date: Tue, 11 Dec 2018 14:16:27 +0000 [thread overview]
Message-ID: <20181211141627.GA526@e107981-ln.cambridge.arm.com> (raw)
In-Reply-To: <1966692.fVZYlVgWHv@aspire.rjw.lan>
On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote:
> On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > > Hi Lorenzo,
> > > >
> > > > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > > > 10:27:08 +0000:
> > > >
> > > > > [+Rafael, Sudeep]
> > > > >
> > > > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > > > Add suspend and resume callbacks. The priority of these are
> > > > > > "_noirq()", to workaround early access to the registers done by the
> > > > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > > >
> > > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > > ---
> > > > > > drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > > > > 1 file changed, 52 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci
> > > > > > return ret;
> > > > > > }
> > > > > >
> > > > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > > > +{
> > > > > > + struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > > > +
> > > > > > + advk_pcie_disable_phy(pcie);
> > > > > > +
> > > > > > + clk_disable_unprepare(pcie->clk);
> > > > >
> > > > > I have noticed it is common practice, still, I would like to check whether
> > > > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > > > callback ?
> > > >
> > > > You are right this is weird. I double checked and for instance,
> > > > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > > > probably other cases where drivers call functions that may sleep from a NOIRQ
> > > > context. I am interested to know if this is valid and if not, what is the
> > > > alternative?
> > > >
> > >
> > > Yes, it is valid. _noirq means that the high-level action handlers
> > > will not be invoked for interrupts occurring during that period, but
> > > that doesn't apply to timer interrupts.
> > >
> > > IOW, don't expect *your* IRQ handler to be invoked then (if this is
> > > not a timer IRQ), but you can sleep.
> >
> > Hi Rafael, all,
> >
> > I did not ask my question (that may be silly) properly apologies. I know
> > that the S2R context allows sleeping the question is, in case
> > clk_disable_unprepare() (and resume counterparts) sleeps,
>
> If it just sleeps, then this is not a problem, but if it actually *waits*
> for something meaningful to happen (which I guess is what you really mean),
> then things may go awry.
>
> > what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> > you said the action handlers (that are possibly required to wake up the eg
> > clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).
>
> So if it waits for an action handler to do something and wake it up, it may
> very well deadlock. I have no idea if that really happens, though.
>
> > The clk API implementations back-ends are beyond my depth, I just wanted
> > to make sure I understand how the S2R flow is expected to work in this
> > specific case.
>
> Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
> (well, there are a few more complications I don't recall exactly, but
> that's the basic rule). If anything depends on them to run, it will block.
Stephen, any comments on this ? I would like to understand if it is safe
to call a clk_*unprepare/prepare_* function (that may have a blocking
back-end waiting on a wake-up event triggered by an IRQ action) in the
suspend/resume NOIRQ phase.
It is not clear how the unprepare/prepare() callers can possibly know
whether it is safe to block at that stage given that IRQ actions are
suspended and the wake-up may never trigger.
Thanks,
Lorenzo
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next prev parent reply other threads:[~2018-12-11 14:16 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-23 14:18 [PATCH 00/12] Bring suspend to RAM support to PCIe Aardvark driver Miquel Raynal
2018-11-23 14:18 ` [PATCH 01/12] PCI: aardvark: configure more registers in the configuration helper Miquel Raynal
2018-11-23 14:18 ` [PATCH 02/12] PCI: aardvark: add reset GPIO support Miquel Raynal
2018-11-23 14:18 ` [PATCH 03/12] PCI: aardvark: add PHY support Miquel Raynal
2018-11-23 14:18 ` [PATCH 04/12] PCI: aardvark: add clock support Miquel Raynal
2018-11-23 14:18 ` [PATCH 05/12] PCI: aardvark: add suspend to RAM support Miquel Raynal
2018-12-03 10:27 ` Lorenzo Pieralisi
2018-12-03 15:38 ` Miquel Raynal
2018-12-03 17:18 ` Lorenzo Pieralisi
2018-12-03 19:19 ` Stephen Boyd
2018-12-03 22:00 ` Rafael J. Wysocki
2018-12-03 22:18 ` Miquel Raynal
2018-12-04 9:45 ` Lorenzo Pieralisi
2018-12-04 21:42 ` Rafael J. Wysocki
2018-12-05 11:00 ` Lorenzo Pieralisi
2018-12-11 14:16 ` Lorenzo Pieralisi [this message]
2018-12-13 9:00 ` Stephen Boyd
2018-12-13 10:53 ` Lorenzo Pieralisi
2018-12-13 14:30 ` Miquel Raynal
2018-12-13 14:52 ` Lorenzo Pieralisi
2018-12-13 21:50 ` Rafael J. Wysocki
2018-12-17 14:54 ` Miquel Raynal
2018-12-18 10:54 ` Rafael J. Wysocki
2018-12-18 14:14 ` Miquel Raynal
2018-11-23 14:18 ` [PATCH 06/12] dt-bindings: PCI: aardvark: describe the reset-gpios property Miquel Raynal
2018-12-11 21:44 ` Rob Herring
2018-11-23 14:18 ` [PATCH 07/12] dt-bindings: PCI: aardvark: describe the clocks property Miquel Raynal
2018-12-11 21:44 ` Rob Herring
2018-11-23 14:18 ` [PATCH 08/12] dt-bindings: PCI: aardvark: describe the PHY property Miquel Raynal
2018-12-11 21:44 ` Rob Herring
2018-11-23 14:18 ` [PATCH 09/12] ARM64: dts: marvell: armada-37xx: declare PCIe reset pin Miquel Raynal
2018-11-23 14:18 ` [PATCH 10/12] ARM64: dts: marvell: armada-3720-espressobin: declare PCIe reset GPIO Miquel Raynal
2018-11-23 14:18 ` [PATCH 11/12] ARM64: dts: marvell: armada-37xx: declare PCIe clock Miquel Raynal
2018-11-23 14:18 ` [PATCH 12/12] ARM64: dts: marvell: armada-3720-espressobin: declare PCIe PHY Miquel Raynal
2018-11-26 14:50 ` [PATCH 00/12] Bring suspend to RAM support to PCIe Aardvark driver Bjorn Helgaas
2018-11-30 13:12 ` Miquel Raynal
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