linux-kernel - Re: [patch 33/37] iommu/arm-smmu-v3: Use msi_get

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Date:   Mon, 29 Nov 2021 13:58:46 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Will Deacon <will@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Megha Dey <megha.dey@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-pci@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        iommu@...ts.linux-foundation.org, dmaengine@...r.kernel.org,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
        Vinod Koul <vkoul@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sinan Kaya <okaya@...nel.org>
Subject: Re: [patch 33/37] iommu/arm-smmu-v3: Use msi_get_virq()

On Mon, Nov 29 2021 at 13:52, Thomas Gleixner wrote:
> On Mon, Nov 29 2021 at 10:55, Will Deacon wrote:
>> On Sat, Nov 27, 2021 at 02:20:59AM +0100, Thomas Gleixner wrote:
>>> +	smmu->evtq.q.irq = msi_get_virq(dev, EVTQ_MSI_INDEX);
>>> +	smmu->gerr_irq = msi_get_virq(dev, GERROR_MSI_INDEX);
>>> +	smmu->priq.q.irq = msi_get_virq(dev, PRIQ_MSI_INDEX);
>>
>> Prviously, if retrieval of the MSI failed then we'd fall back to wired
>> interrupts. Now, I think we'll clobber the interrupt with 0 instead. Can
>> we make the assignments to smmu->*irq here conditional on the MSI being
>> valid, please?
>
> So the wired irq number is in ->irq already and MSI does an override
> if available. Not really obvious...

But, this happens right after:

     ret = platform_msi_domain_alloc_irqs(dev, nvec, arm_smmu_write_msi_msg);

So if that succeeded then the descriptors exist and have interrupts
assigned.

Thanks,

        tglx