linux-kernel - Re: [PATCH v2] PCI: pciehp: Make sure pciehp

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Date:   Sun, 9 Feb 2020 13:55:43 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Stuart Hayes <stuart.w.hayes@...il.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>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Enzo Matsumiya <ematsumiya@...e.de>
Subject: Re: [PATCH v2] PCI: pciehp: Make sure pciehp_isr clears interrupt
 events

On Tue, Jan 28, 2020 at 06:51:51PM -0600, Bjorn Helgaas wrote:
> On Wed, Nov 20, 2019 at 05:20:43PM -0500, Stuart Hayes wrote:
> > -	pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, events);
> > +	if (status) {
> > +		pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, status);
> > +
> > +		/*
> > +		 * If MSI per-vector masking is not supported by the port,
> > +		 * all of the event bits must be zero before the port will
> > +		 * send a new interrupt (see PCI Express Base Specification
> > +		 * Revision 5.0 Version 1.0, section 6.7.3.4, "Software
> > +		 * Notification of Hot-Plug Events"). So in that case, if
> > +		 * event bit gets set between the read and the write of
> > +		 * PCI_EXP_SLTSTA, we need to loop back and try again.
> > +		 */
> > +		if (!ctrl->pvm_capable) {
> 
> I don't know what whether the MSI vector is masked or not at this
> point

I think MSIs are handled by handle_edge_irq(), which, unlike
handle_level_irq(), does not mask the IRQ by default.

We could call disable_irq_nosync() / enable_irq() to mask the IRQ and
immediately unmask it after writing to the slot status register if the
interrupt uses MSI / MSI-X (and not INTx), thereby forcing another
interrupt if new bits have been set in the meantime.  But I suspect this
approach may not work if PVM is unsupported.


> I see that Lukas took a look at this earlier; I'd really like to have
> his reviewed-by, since he's the expert on this code.

Hm, should we add an entry for pciehp to MAINTAINERS and list me as R: or M:?

Thanks,

Lukas