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SubjectRe: [PATCH v4] PCI: dwc: pci-dra7xx: Fix MSI IRQ handling
On Mon, Mar 30, 2020 at 11:29:52AM -0500, Bjorn Helgaas wrote:
> [+cc Marc, Thomas]
>
> 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:
>
> If the Port is enabled for edge-triggered interrupt signaling using
> MSI or MSI-X, an interrupt message must be sent every time the
> logical AND of the following conditions transitions from FALSE to
> TRUE:
>
> - The associated vector is unmasked (not applicable if MSI does
> not support PVM).
>
> - The Hot-Plug Interrupt Enable bit in the Slot Control register
> is set to 1b.
>
> - At least one hot-plug event status bit in the Slot Status
> register and its associated enable bit in the Slot Control
> register are both set to 1b.
>
> and this related commit: https://git.kernel.org/linus/fad214b0aa72

and this one: https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?id=87d94ad41bd2

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