linux-kernel - Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge

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Date:   Thu, 20 Apr 2017 10:20:31 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        David Laight <david.laight@...lab.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge

On 19/04/2017 13:19, Mason wrote:

> My biggest problem is that tango_unmask() is never called.

FTR, the missing incantation was:
Explicitly calling tango_{mask/unmask/ack} from the corresponding msi_{mask/unmask/ack}

Marc, I have one nagging doubt, wrt splitting MSI line selection
and MSI enable.

tango_irq_domain_alloc : finds an available MSI 'j' to allocate
tango_irq_domain_free : release MSI 'j'
tango_unmask : enable MSI 'j'
tango_mask : disable MSI 'j'

Is the following scenario guaranteed to never happen?

tango_irq_domain_alloc // alloc 0
tango_irq_domain_free  // free 0
tango_irq_domain_alloc // alloc 0
tango_unmask // enable 0
tango_unmask // enable 0 = NOP
tango_mask   // disable 0

In this theoretical scenario, we would be left with a non-functional
MSI 0.

Regards.