linux-kernel - Re: [PATCH RFC v2 04/18] irq/dev-msi: Introduce APIs to allocate/free dev-msi interrupts

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Date:   Wed, 22 Jul 2020 10:05:52 -0700
From:   "Dey, Megha" <megha.dey@...el.com>
To:     Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>
CC:     <vkoul@...nel.org>, <maz@...nel.org>, <bhelgaas@...gle.com>,
        <rafael@...nel.org>, <gregkh@...uxfoundation.org>,
        <tglx@...utronix.de>, <hpa@...or.com>,
        <alex.williamson@...hat.com>, <jacob.jun.pan@...el.com>,
        <ashok.raj@...el.com>, <yi.l.liu@...el.com>, <baolu.lu@...el.com>,
        <kevin.tian@...el.com>, <sanjay.k.kumar@...el.com>,
        <tony.luck@...el.com>, <jing.lin@...el.com>,
        <dan.j.williams@...el.com>, <kwankhede@...dia.com>,
        <eric.auger@...hat.com>, <parav@...lanox.com>,
        <dave.hansen@...el.com>, <netanelg@...lanox.com>,
        <shahafs@...lanox.com>, <yan.y.zhao@...ux.intel.com>,
        <pbonzini@...hat.com>, <samuel.ortiz@...el.com>,
        <mona.hossain@...el.com>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <linux-pci@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH RFC v2 04/18] irq/dev-msi: Introduce APIs to allocate/free
 dev-msi interrupts



On 7/21/2020 9:25 AM, Jason Gunthorpe wrote:
> On Tue, Jul 21, 2020 at 09:02:41AM -0700, Dave Jiang wrote:
>> From: Megha Dey <megha.dey@...el.com>
>>
>> The dev-msi interrupts are to be allocated/freed only for custom devices,
>> not standard PCI-MSIX devices.
>>
>> These interrupts are device-defined and they are distinct from the already
>> existing msi interrupts:
>> pci-msi: Standard PCI MSI/MSI-X setup format
>> platform-msi: Platform custom, but device-driver opaque MSI setup/control
>> arch-msi: fallback for devices not assigned to the generic PCI domain
>> dev-msi: device defined IRQ domain for ancillary devices. For e.g. DSA
>> portal devices use device specific IMS(Interrupt message store) interrupts.
>>
>> dev-msi interrupts are represented by their own device-type. That means
>> dev->msi_list is never contended for different interrupt types. It
>> will either be all PCI-MSI or all device-defined.
> 
> Not sure I follow this, where is the enforcement that only dev-msi or
> normal MSI is being used at one time on a single struct device?
> 

So, in the dev_msi_alloc_irqs, I first check if the dev_is_pci..
If it is a pci device, it is forbidden to use dev-msi and must use the 
pci subsystem calls. dev-msi is to be used for all other custom devices, 
mdev or otherwise.

> Jason
>