linux-kernel - Re: [PATCH] PCI: pciehp: Make sure pciehp

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Date:   Thu, 14 Nov 2019 03:50:22 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Stuart Hayes <stuart.w.hayes@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: pciehp: Make sure pciehp_isr clears interrupt events

On Wed, Nov 13, 2019 at 03:58:51PM -0600, Stuart Hayes wrote:
> The hotplug port I'm seeing the issue with is an AMD "Starship/Matisse GPP
> Bridge" (1022/1483), which uses an MSI interrupt (PCI-MSI chip).
[...]
> And because individual event enable bits in the slot control register aren't
> cleared on each interrupt, I interpret this to mean that an interrupt message
> will be sent every time that the event status bits in the slot status register
> transition from all zeros to at least one event status bit being 1.  Once one
> of those event status bits is 1, the logical AND of the three conditions above
> will not transition from FALSE to TRUE again until all of the (enabled) event
> status bits in the slot status register all go to zero, which is what my patch
> is intended to ensure.

Understood now, thanks.

I'd suggest adding a flag "unsigned int pvm_capable;" to struct controller
below "u32 slot_cap" (in the "capabilities and quirks" section),
setting that flag in pcie_init() from dev->msi_cap + PCI_MSI_FLAGS
(& PCI_MSI_FLAGS_MASKBIT) and amending pciehp_isr() to check for that
flag and re-read / re-write the Slot Status register until it's all zeroes.
That would make the reason for the modifications to pciehp_isr() explicit.
Please try to make the modifications to pciehp_isr() as small and simple
as possible.  Maybe it's worthwhile to put them in a separate static
function which is called from pciehp_isr(), I don't know.

Please mention the PCI vendor / device IDs in the commit message
and provide a reference to the PCIe Base Spec section you've quoted
above.

Thanks,

Lukas