linux-kernel - Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated

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Date:   Wed, 30 Jun 2021 21:46:01 +0100
From:   Peter Robinson <pbrobinson@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org, Shawn Lin <shawn.lin@...k-chips.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Michal Simek <michal.simek@...inx.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with
 clocks gated

On Wed, Jun 30, 2021 at 9:30 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Wed, Jun 30, 2021 at 09:59:58PM +0200, Javier Martinez Canillas wrote:
> > On 6/30/21 8:59 PM, Bjorn Helgaas wrote:
> > > [+cc Michal, Jingoo, Thierry, Jonathan]
> >
> > [snip]
> >
> > >
> > > I think the above commit log is perfectly accurate, but all the
> > > details might suggest that this is something specific to rockchip or
> > > CONFIG_DEBUG_SHIRQ, which it isn't, and they might obscure the
> > > fundamental problem, which is actually very simple: we registered IRQ
> > > handlers before we were ready for them to be called.
> > >
> > > I propose the following commit log in the hope that it would help
> > > other driver authors to make similar fixes:
> > >
> > >     PCI: rockchip: Register IRQ handlers after device and data are ready
> > >
> > >     An IRQ handler may be called at any time after it is registered, so
> > >     anything it relies on must be ready before registration.
> > >
> > >     rockchip_pcie_subsys_irq_handler() and rockchip_pcie_client_irq_handler()
> > >     read registers in the PCIe controller, but we registered them before
> > >     turning on clocks to the controller.  If either is called before the clocks
> > >     are turned on, the register reads fail and the machine hangs.
> > >
> > >     Similarly, rockchip_pcie_legacy_int_handler() uses rockchip->irq_domain,
> > >     but we installed it before initializing irq_domain.
> > >
> > >     Register IRQ handlers after their data structures are initialized and
> > >     clocks are enabled.
> > >
> > > If this is inaccurate or omits something important, let me know.  I
> > > can make any updates locally.
> > >
> >
> > I think your description is accurate and agree that the commit message may
> > be misleading. As you said, this is a general problem and the fact that an
> > IRQ is shared and CONFIG_DEBUG_SHIRQ fires a spurious interrupt just make
> > the assumptions in the driver to fall apart.
> >
> > But maybe you can also add a paragraph that mentions the CONFIG_DEBUG_SHIRQ
> > option and shared interrupts? That way, other driver authors could know that
> > by enabling this an underlying problem might be exposed for them to fix.
>
> Good idea, thanks!  I added this; is it something like what you had in
> mind?
>
>     Found by enabling CONFIG_DEBUG_SHIRQ, which calls the IRQ handler when it
>     is being unregistered.  An error during the probe path might cause this
>     unregistration and IRQ handler execution before the device or data
>     structure init has finished.

Would it make sense to enable CONFIG_DEBUG_SHIRQ in defconfig to
better pick up these problems?

Peter