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

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Message-ID: <b61614bd-10e4-25eb-95bc-fd8939d4449f@arm.com>
Date:   Thu, 20 Apr 2017 10:43:11 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Mason <slash.tmp@...e.fr>, 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 20/04/17 09:20, Mason wrote:
> 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}

Using irq_chip_mask_parent and co, you mean?

> 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.

I'm not sure I get the example above, and what the various alloc/free
calls have to do with anything. If you have unbalanced
enable/disable_irq, you loose. Don't do that.

	M.
-- 
Jazz is not dead. It just smells funny...