linux-kernel - Re: [PATCH] PCI: let pci_request_irq properly deal with threaded interrupts

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Message-ID: <96285966-f2d2-c820-7f38-de22deeb8074@gmail.com>
Date:   Fri, 3 Aug 2018 22:55:00 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: let pci_request_irq properly deal with threaded
 interrupts

On 03.08.2018 21:40, Thomas Gleixner wrote:
> On Fri, 3 Aug 2018, Heiner Kallweit wrote:
>> On 03.08.2018 16:09, Thomas Gleixner wrote:
>>> On Wed, 1 Aug 2018, Heiner Kallweit wrote:
>>>> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
>>>> index 4ca2fd46..ba6da943 100644
>>>> --- a/kernel/irq/msi.c
>>>> +++ b/kernel/irq/msi.c
>>>> @@ -289,6 +289,9 @@ struct irq_domain *msi_create_irq_domain(struct fwnode_handle *fwnode,
>>>>         if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
>>>>                 msi_domain_update_chip_ops(info);
>>>>
>>>> +       /* MSI is oneshot-safe in general */
>>>> +       info->chip->flags |= IRQCHIP_ONESHOT_SAFE;
>>>> +
>>>>         domain = irq_domain_create_hierarchy(parent, IRQ_DOMAIN_FLAG_MSI, 0,
>>>
>>> Looks about right, though there might be dragons. MSI is not always as sane
>>> as it should be...
>>>
>> When saying "MSI isn't always sane", are you referring to the hardware or
>> the controller driver implementation? Basically for me the question is
>> whether we would be able to fix the issue if we meet such a dragon,
>> or whether we would have to revert the change.
> 
> It's hardware unfortunately, so it might be a revert. PCI-MSI should be
> safe, but the wild MSI variants in SoCs might be the actual dragon caves.
> 

pci_msi_create_irq_domain() is used by controller drivers for PCI(e)
controllers in SoCs like Mediatek, Armada, ..
I assume you're referring to some other (non-PCI) SoC-internal
MSI mechanism when saying "wild variants", right?

>> Do you think the chance of a dragon is low enough? Or better add the
>> flag only to the X86 PCI MSI irqchip for now?
> 
> I think PCI-MSI in general would be not too risky. Famous last words.
> 
> Thanks,
> 
> 	tglx
>