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 14:35:15 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     "Dey, Megha" <megha.dey@...el.com>
Cc:     Dave Jiang <dave.jiang@...el.com>, 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 Wed, Jul 22, 2020 at 10:05:52AM -0700, Dey, Megha wrote:
> 
> 
> 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.

What prevents creating a dev-msi directly on the struct pci_device ?

Jason