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, 5 Aug 2020 20:19:36 +0000
From:   "Dey, Megha" <megha.dey@...el.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
CC:     "Jiang, Dave" <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "maz@...nel.org" <maz@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
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        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
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        "Hansen, Dave" <dave.hansen@...el.com>,
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        "Ortiz, Samuel" <samuel.ortiz@...el.com>,
        "Hossain, Mona" <mona.hossain@...el.com>,
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Subject: RE: [PATCH RFC v2 04/18] irq/dev-msi: Introduce APIs to allocate/free
 dev-msi interrupts

Hi Jason,

> -----Original Message-----
> From: Jason Gunthorpe <jgg@...lanox.com>
> Sent: Wednesday, July 22, 2020 10:35 AM
> To: Dey, Megha <megha.dey@...el.com>
> Cc: Jiang, Dave <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; Pan, Jacob
> jun <jacob.jun.pan@...el.com>; Raj, Ashok <ashok.raj@...el.com>; Liu, Yi L
> <yi.l.liu@...el.com>; Lu, Baolu <baolu.lu@...el.com>; Tian, Kevin
> <kevin.tian@...el.com>; Kumar, Sanjay K <sanjay.k.kumar@...el.com>; Luck,
> Tony <tony.luck@...el.com>; Lin, Jing <jing.lin@...el.com>; Williams, Dan J
> <dan.j.williams@...el.com>; kwankhede@...dia.com; eric.auger@...hat.com;
> parav@...lanox.com; Hansen, Dave <dave.hansen@...el.com>;
> netanelg@...lanox.com; shahafs@...lanox.com; yan.y.zhao@...ux.intel.com;
> pbonzini@...hat.com; Ortiz, Samuel <samuel.ortiz@...el.com>; Hossain, Mona
> <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 ?

In the next patchset, I have explicitly added code which denies PCI devices from using the dev_msi alloc/free APIS
> 
> Jason