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From: Bjorn Helgaas <helgaas@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Vignesh Raghavendra <vigneshr@ti.com>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Andrew Murray <amurray@thegoodpenguin.co.uk>,
	linux-omap@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH v4] PCI: dwc: pci-dra7xx: Fix MSI IRQ handling
Date: Tue, 31 Mar 2020 11:09:14 -0500	[thread overview]
Message-ID: <20200331160914.GA195472@google.com> (raw)
In-Reply-To: <87zhbxv979.fsf@nanos.tec.linutronix.de>

On Mon, Mar 30, 2020 at 11:12:10PM +0200, Thomas Gleixner wrote:
> Bjorn Helgaas <helgaas@kernel.org> writes:
> > On Fri, Mar 27, 2020 at 03:24:34PM +0530, Vignesh Raghavendra wrote:
> >> Due an issue with PCIe wrapper around DWC PCIe IP on dra7xx, driver
> >> needs to ensure that there are no pending MSI IRQ vector set (i.e
> >> PCIE_MSI_INTR0_STATUS reads 0 at least once) before exiting IRQ handler.
> >> Else, the dra7xx PCIe wrapper will not register new MSI IRQs even though
> >> PCIE_MSI_INTR0_STATUS shows IRQs are pending.
> >
> > I'm not an IRQ guy (real IRQ guys CC'd), but I'm wondering if this is
> > really a symptom of a problem in the generic DWC IRQ handling, not a
> > problem in dra7xx itself.
> >
> > I thought it was sort of standard behavior that a device would not
> > send a new MSI unless there was a transition from "no status bits set"
> > to "at least one status bit set".  I'm looking at this text from the
> > PCIe r5.0 spec, sec 6.7.3.4:
> 
> That's for the device side. But this is the host side and that consists
> of two components:
> 
>      1) The actual PCIe host controller (DWC)
> 
>      2) Some hardware wrapper around #1 to glue the host controller IP
>         into the TI SoC.
> 
> #1 contains a MSI message receiver unit. PCIE_MSI_INTR0_STATUS is part
> that.
> 
> If there is a MSI message sent to the host then the bit which is
> corresponding to the sent message (vector) is set in the status
> register. If a bit is set in the status register then the host
> controller raises an interrupt at its output.
> 
> Here, if I deciphered the above changelog correctly, comes the wrapper
> glue #2 into play, which seems to be involved in forwarding the host
> controller interrupt to the CPU's interrupt controller (GIC) and that
> forwarding mechanism seems to have some issue.

Sorry for muddying the waters, and thanks for clarifying it, Thomas.

This patch is on its way to v5.7, and I guess we'll worry about
whether the interrupt chip reimplementation is overkill later.

Bjorn

      reply	other threads:[~2020-03-31 16:09 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-27  9:54 [PATCH v4] PCI: dwc: pci-dra7xx: Fix MSI IRQ handling Vignesh Raghavendra
2020-03-27 15:01 ` Lorenzo Pieralisi
2020-03-30 16:29 ` Bjorn Helgaas
2020-03-30 16:37   ` Bjorn Helgaas
2020-03-31 11:05     ` Vignesh Raghavendra
2020-03-30 21:12   ` Thomas Gleixner
2020-03-31 16:09     ` Bjorn Helgaas [this message]

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